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張 旭

Active Record Associations - Ruby on Rails Guides - 0 views

  • With Active Record associations, we can streamline these - and other - operations by declaratively telling Rails that there is a connection between the two models.
  • belongs_to has_one has_many has_many :through has_one :through has_and_belongs_to_many
  • an association is a connection between two Active Record models
  • ...195 more annotations...
  • Associations are implemented using macro-style calls, so that you can declaratively add features to your models
  • A belongs_to association sets up a one-to-one connection with another model, such that each instance of the declaring model "belongs to" one instance of the other model.
  • belongs_to associations must use the singular term.
  • belongs_to
  • A has_one association also sets up a one-to-one connection with another model, but with somewhat different semantics (and consequences).
  • This association indicates that each instance of a model contains or possesses one instance of another model
  • belongs_to
  • A has_many association indicates a one-to-many connection with another model.
  • This association indicates that each instance of the model has zero or more instances of another model.
  • belongs_to
  • A has_many :through association is often used to set up a many-to-many connection with another model
  • This association indicates that the declaring model can be matched with zero or more instances of another model by proceeding through a third model.
  • through:
  • through:
  • The collection of join models can be managed via the API
  • new join models are created for newly associated objects, and if some are gone their rows are deleted.
  • The has_many :through association is also useful for setting up "shortcuts" through nested has_many associations
  • A has_one :through association sets up a one-to-one connection with another model. This association indicates that the declaring model can be matched with one instance of another model by proceeding through a third model.
  • A has_and_belongs_to_many association creates a direct many-to-many connection with another model, with no intervening model.
  • id: false
  • The has_one relationship says that one of something is yours
  • using t.references :supplier instead.
  • declare a many-to-many relationship is to use has_many :through. This makes the association indirectly, through a join model
  • set up a has_many :through relationship if you need to work with the relationship model as an independent entity
  • set up a has_and_belongs_to_many relationship (though you'll need to remember to create the joining table in the database).
  • use has_many :through if you need validations, callbacks, or extra attributes on the join model
  • With polymorphic associations, a model can belong to more than one other model, on a single association.
  • belongs_to :imageable, polymorphic: true
  • a polymorphic belongs_to declaration as setting up an interface that any other model can use.
    • 張 旭
       
      _id 記錄的是不同類型的外連鍵 id;_type 記錄的是不同類型的表格名稱。
  • In designing a data model, you will sometimes find a model that should have a relation to itself
  • add a references column to the model itself
  • Controlling caching Avoiding name collisions Updating the schema Controlling association scope Bi-directional associations
  • All of the association methods are built around caching, which keeps the result of the most recent query available for further operations.
  • it is a bad idea to give an association a name that is already used for an instance method of ActiveRecord::Base. The association method would override the base method and break things.
  • You are responsible for maintaining your database schema to match your associations.
  • belongs_to associations you need to create foreign keys
  • has_and_belongs_to_many associations you need to create the appropriate join table
  • If you create an association some time after you build the underlying model, you need to remember to create an add_column migration to provide the necessary foreign key.
  • Active Record creates the name by using the lexical order of the class names
  • So a join between customer and order models will give the default join table name of "customers_orders" because "c" outranks "o" in lexical ordering.
  • For example, one would expect the tables "paper_boxes" and "papers" to generate a join table name of "papers_paper_boxes" because of the length of the name "paper_boxes", but it in fact generates a join table name of "paper_boxes_papers" (because the underscore '' is lexicographically _less than 's' in common encodings).
  • id: false
  • pass id: false to create_table because that table does not represent a model
  • By default, associations look for objects only within the current module's scope.
  • will work fine, because both the Supplier and the Account class are defined within the same scope.
  • To associate a model with a model in a different namespace, you must specify the complete class name in your association declaration:
  • class_name
  • class_name
  • Active Record provides the :inverse_of option
    • 張 旭
       
      意思是說第一次比較兩者的 first_name 是相同的;但透過 c 實體修改 first_name 之後,再次比較就不相同了,因為兩個是記憶體裡面兩個不同的物件。
  • preventing inconsistencies and making your application more efficient
  • Every association will attempt to automatically find the inverse association and set the :inverse_of option heuristically (based on the association name)
  • In database terms, this association says that this class contains the foreign key.
  • In all of these methods, association is replaced with the symbol passed as the first argument to belongs_to.
  • (force_reload = false)
  • The association method returns the associated object, if any. If no associated object is found, it returns nil.
  • the cached version will be returned.
  • The association= method assigns an associated object to this object.
  • Behind the scenes, this means extracting the primary key from the associate object and setting this object's foreign key to the same value.
  • The build_association method returns a new object of the associated type
  • but the associated object will not yet be saved.
  • The create_association method returns a new object of the associated type
  • once it passes all of the validations specified on the associated model, the associated object will be saved
  • raises ActiveRecord::RecordInvalid if the record is invalid.
  • dependent
  • counter_cache
  • :autosave :class_name :counter_cache :dependent :foreign_key :inverse_of :polymorphic :touch :validate
  • finding the number of belonging objects more efficient.
  • Although the :counter_cache option is specified on the model that includes the belongs_to declaration, the actual column must be added to the associated model.
  • add a column named orders_count to the Customer model.
  • :destroy, when the object is destroyed, destroy will be called on its associated objects.
  • deleted directly from the database without calling their destroy method.
  • Rails will not create foreign key columns for you
  • The :inverse_of option specifies the name of the has_many or has_one association that is the inverse of this association
  • set the :touch option to :true, then the updated_at or updated_on timestamp on the associated object will be set to the current time whenever this object is saved or destroyed
  • specify a particular timestamp attribute to update
  • If you set the :validate option to true, then associated objects will be validated whenever you save this object
  • By default, this is false: associated objects will not be validated when this object is saved.
  • where includes readonly select
  • make your code somewhat more efficient
  • no need to use includes for immediate associations
  • will be read-only when retrieved via the association
  • The select method lets you override the SQL SELECT clause that is used to retrieve data about the associated object
  • using the association.nil?
  • Assigning an object to a belongs_to association does not automatically save the object. It does not save the associated object either.
  • In database terms, this association says that the other class contains the foreign key.
  • the cached version will be returned.
  • :as :autosave :class_name :dependent :foreign_key :inverse_of :primary_key :source :source_type :through :validate
  • Setting the :as option indicates that this is a polymorphic association
  • :nullify causes the foreign key to be set to NULL. Callbacks are not executed.
  • It's necessary not to set or leave :nullify option for those associations that have NOT NULL database constraints.
  • The :source_type option specifies the source association type for a has_one :through association that proceeds through a polymorphic association.
  • The :source option specifies the source association name for a has_one :through association.
  • The :through option specifies a join model through which to perform the query
  • more efficient by including representatives in the association from suppliers to accounts
  • When you assign an object to a has_one association, that object is automatically saved (in order to update its foreign key).
  • If either of these saves fails due to validation errors, then the assignment statement returns false and the assignment itself is cancelled.
  • If the parent object (the one declaring the has_one association) is unsaved (that is, new_record? returns true) then the child objects are not saved.
  • If you want to assign an object to a has_one association without saving the object, use the association.build method
  • collection(force_reload = false) collection<<(object, ...) collection.delete(object, ...) collection.destroy(object, ...) collection=(objects) collection_singular_ids collection_singular_ids=(ids) collection.clear collection.empty? collection.size collection.find(...) collection.where(...) collection.exists?(...) collection.build(attributes = {}, ...) collection.create(attributes = {}) collection.create!(attributes = {})
  • In all of these methods, collection is replaced with the symbol passed as the first argument to has_many, and collection_singular is replaced with the singularized version of that symbol.
  • The collection<< method adds one or more objects to the collection by setting their foreign keys to the primary key of the calling model
  • The collection.delete method removes one or more objects from the collection by setting their foreign keys to NULL.
  • objects will be destroyed if they're associated with dependent: :destroy, and deleted if they're associated with dependent: :delete_all
  • The collection.destroy method removes one or more objects from the collection by running destroy on each object.
  • The collection_singular_ids method returns an array of the ids of the objects in the collection.
  • The collection_singular_ids= method makes the collection contain only the objects identified by the supplied primary key values, by adding and deleting as appropriate
  • The default strategy for has_many :through associations is delete_all, and for has_many associations is to set the foreign keys to NULL.
  • The collection.clear method removes all objects from the collection according to the strategy specified by the dependent option
  • uses the same syntax and options as ActiveRecord::Base.find
  • The collection.where method finds objects within the collection based on the conditions supplied but the objects are loaded lazily meaning that the database is queried only when the object(s) are accessed.
  • The collection.build method returns one or more new objects of the associated type. These objects will be instantiated from the passed attributes, and the link through their foreign key will be created, but the associated objects will not yet be saved.
  • The collection.create method returns a new object of the associated type. This object will be instantiated from the passed attributes, the link through its foreign key will be created, and, once it passes all of the validations specified on the associated model, the associated object will be saved.
  • :as :autosave :class_name :dependent :foreign_key :inverse_of :primary_key :source :source_type :through :validate
  • :delete_all causes all the associated objects to be deleted directly from the database (so callbacks will not execute)
  • :nullify causes the foreign keys to be set to NULL. Callbacks are not executed.
  • where includes readonly select
  • :conditions :through :polymorphic :foreign_key
  • By convention, Rails assumes that the column used to hold the primary key of the association is id. You can override this and explicitly specify the primary key with the :primary_key option.
  • The :source option specifies the source association name for a has_many :through association.
  • You only need to use this option if the name of the source association cannot be automatically inferred from the association name.
  • The :source_type option specifies the source association type for a has_many :through association that proceeds through a polymorphic association.
  • The :through option specifies a join model through which to perform the query.
  • has_many :through associations provide a way to implement many-to-many relationships,
  • By default, this is true: associated objects will be validated when this object is saved.
  • where extending group includes limit offset order readonly select uniq
  • If you use a hash-style where option, then record creation via this association will be automatically scoped using the hash
  • The extending method specifies a named module to extend the association proxy.
  • Association extensions
  • The group method supplies an attribute name to group the result set by, using a GROUP BY clause in the finder SQL.
  • has_many :line_items, -> { group 'orders.id' },                        through: :orders
  • more efficient by including line items in the association from customers to orders
  • The limit method lets you restrict the total number of objects that will be fetched through an association.
  • The offset method lets you specify the starting offset for fetching objects via an association
  • The order method dictates the order in which associated objects will be received (in the syntax used by an SQL ORDER BY clause).
  • Use the distinct method to keep the collection free of duplicates.
  • mostly useful together with the :through option
  • -> { distinct }
  • .all.inspect
  • If you want to make sure that, upon insertion, all of the records in the persisted association are distinct (so that you can be sure that when you inspect the association that you will never find duplicate records), you should add a unique index on the table itself
  • unique: true
  • Do not attempt to use include? to enforce distinctness in an association.
  • multiple users could be attempting this at the same time
  • checking for uniqueness using something like include? is subject to race conditions
  • When you assign an object to a has_many association, that object is automatically saved (in order to update its foreign key).
  • If any of these saves fails due to validation errors, then the assignment statement returns false and the assignment itself is cancelled.
  • If the parent object (the one declaring the has_many association) is unsaved (that is, new_record? returns true) then the child objects are not saved when they are added
  • All unsaved members of the association will automatically be saved when the parent is saved.
  • assign an object to a has_many association without saving the object, use the collection.build method
  • collection(force_reload = false) collection<<(object, ...) collection.delete(object, ...) collection.destroy(object, ...) collection=(objects) collection_singular_ids collection_singular_ids=(ids) collection.clear collection.empty? collection.size collection.find(...) collection.where(...) collection.exists?(...) collection.build(attributes = {}) collection.create(attributes = {}) collection.create!(attributes = {})
  • If the join table for a has_and_belongs_to_many association has additional columns beyond the two foreign keys, these columns will be added as attributes to records retrieved via that association.
  • Records returned with additional attributes will always be read-only
  • If you require this sort of complex behavior on the table that joins two models in a many-to-many relationship, you should use a has_many :through association instead of has_and_belongs_to_many.
  • aliased as collection.concat and collection.push.
  • The collection.delete method removes one or more objects from the collection by deleting records in the join table
  • not destroy the objects
  • The collection.destroy method removes one or more objects from the collection by running destroy on each record in the join table, including running callbacks.
  • not destroy the objects.
  • The collection.clear method removes every object from the collection by deleting the rows from the joining table.
  • not destroy the associated objects.
  • The collection.find method finds objects within the collection. It uses the same syntax and options as ActiveRecord::Base.find.
  • The collection.where method finds objects within the collection based on the conditions supplied but the objects are loaded lazily meaning that the database is queried only when the object(s) are accessed.
  • The collection.exists? method checks whether an object meeting the supplied conditions exists in the collection.
  • The collection.build method returns a new object of the associated type.
  • the associated object will not yet be saved.
  • the associated object will be saved.
  • The collection.create method returns a new object of the associated type.
  • it passes all of the validations specified on the associated model
  • :association_foreign_key :autosave :class_name :foreign_key :join_table :validate
  • The :foreign_key and :association_foreign_key options are useful when setting up a many-to-many self-join.
  • Rails assumes that the column in the join table used to hold the foreign key pointing to the other model is the name of that model with the suffix _id added.
  • If you set the :autosave option to true, Rails will save any loaded members and destroy members that are marked for destruction whenever you save the parent object.
  • By convention, Rails assumes that the column in the join table used to hold the foreign key pointing to this model is the name of this model with the suffix _id added.
  • By default, this is true: associated objects will be validated when this object is saved.
  • where extending group includes limit offset order readonly select uniq
  • set conditions via a hash
  • In this case, using @parts.assemblies.create or @parts.assemblies.build will create orders where the factory column has the value "Seattle"
  • If you use a hash-style where, then record creation via this association will be automatically scoped using the hash
  • using a GROUP BY clause in the finder SQL.
  • Use the uniq method to remove duplicates from the collection.
  • assign an object to a has_and_belongs_to_many association, that object is automatically saved (in order to update the join table).
  • If any of these saves fails due to validation errors, then the assignment statement returns false and the assignment itself is cancelled.
  • If the parent object (the one declaring the has_and_belongs_to_many association) is unsaved (that is, new_record? returns true) then the child objects are not saved when they are added.
  • If you want to assign an object to a has_and_belongs_to_many association without saving the object, use the collection.build method.
  • Normal callbacks hook into the life cycle of Active Record objects, allowing you to work with those objects at various points
  • define association callbacks by adding options to the association declaration
  • Rails passes the object being added or removed to the callback.
  • stack callbacks on a single event by passing them as an array
  • If a before_add callback throws an exception, the object does not get added to the collection.
  • if a before_remove callback throws an exception, the object does not get removed from the collection
  • extend these objects through anonymous modules, adding new finders, creators, or other methods.
  • order_number
  • use a named extension module
  • proxy_association.owner returns the object that the association is a part of.
張 旭

Active Record Validations - Ruby on Rails Guides - 0 views

  • validates :name, presence: true
  • Validations are used to ensure that only valid data is saved into your database
  • Model-level validations are the best way to ensure that only valid data is saved into your database.
  • ...117 more annotations...
  • native database constraints
  • client-side validations
  • controller-level validations
  • Database constraints and/or stored procedures make the validation mechanisms database-dependent and can make testing and maintenance more difficult
  • Client-side validations can be useful, but are generally unreliable
  • combined with other techniques, client-side validation can be a convenient way to provide users with immediate feedback
  • it's a good idea to keep your controllers skinny
  • model-level validations are the most appropriate in most circumstances.
  • Active Record uses the new_record? instance method to determine whether an object is already in the database or not.
  • Creating and saving a new record will send an SQL INSERT operation to the database. Updating an existing record will send an SQL UPDATE operation instead. Validations are typically run before these commands are sent to the database
  • The bang versions (e.g. save!) raise an exception if the record is invalid.
  • save and update return false
  • create just returns the object
  • skip validations, and will save the object to the database regardless of its validity.
  • be used with caution
  • update_all
  • save also has the ability to skip validations if passed validate: false as argument.
  • save(validate: false)
  • valid? triggers your validations and returns true if no errors
  • After Active Record has performed validations, any errors found can be accessed through the errors.messages instance method
  • By definition, an object is valid if this collection is empty after running validations.
  • validations are not run when using new.
  • invalid? is simply the inverse of valid?.
  • To verify whether or not a particular attribute of an object is valid, you can use errors[:attribute]. I
  • only useful after validations have been run
  • Every time a validation fails, an error message is added to the object's errors collection,
  • All of them accept the :on and :message options, which define when the validation should be run and what message should be added to the errors collection if it fails, respectively.
  • validates that a checkbox on the user interface was checked when a form was submitted.
  • agree to your application's terms of service
  • 'acceptance' does not need to be recorded anywhere in your database (if you don't have a field for it, the helper will just create a virtual attribute).
  • It defaults to "1" and can be easily changed.
  • use this helper when your model has associations with other models and they also need to be validated
  • valid? will be called upon each one of the associated objects.
  • work with all of the association types
  • Don't use validates_associated on both ends of your associations.
    • 張 旭
       
      關聯式的物件驗證,在其中一方啟動就好了!
  • each associated object will contain its own errors collection
  • errors do not bubble up to the calling model
  • when you have two text fields that should receive exactly the same content
  • This validation creates a virtual attribute whose name is the name of the field that has to be confirmed with "_confirmation" appended.
  • To require confirmation, make sure to add a presence check for the confirmation attribute
  • this set can be any enumerable object.
  • The exclusion helper has an option :in that receives the set of values that will not be accepted for the validated attributes.
  • :in option has an alias called :within
  • validates the attributes' values by testing whether they match a given regular expression, which is specified using the :with option.
  • attribute does not match the regular expression by using the :without option.
  • validates that the attributes' values are included in a given set
  • :in option has an alias called :within
  • specify length constraints
  • :minimum
  • :maximum
  • :in (or :within)
  • :is - The attribute length must be equal to the given value.
  • :wrong_length, :too_long, and :too_short options and %{count} as a placeholder for the number corresponding to the length constraint being used.
  • split the value in a different way using the :tokenizer option:
    • 張 旭
       
      自己提供切割算字數的方式
  • validates that your attributes have only numeric values
  • By default, it will match an optional sign followed by an integral or floating point number.
  • set :only_integer to true.
  • allows a trailing newline character.
  • :greater_than
  • :greater_than_or_equal_to
  • :equal_to
  • :less_than
  • :less_than_or_equal_to
  • :odd - Specifies the value must be an odd number if set to true.
  • :even - Specifies the value must be an even number if set to true.
  • validates that the specified attributes are not empty
  • if the value is either nil or a blank string
  • validate associated records whose presence is required, you must specify the :inverse_of option for the association
  • inverse_of
  • an association is present, you'll need to test whether the associated object itself is present, and not the foreign key used to map the association
  • false.blank? is true
  • validate the presence of a boolean field
  • ensure the value will NOT be nil
  • validates that the specified attributes are absent
  • not either nil or a blank string
  • be sure that an association is absent
  • false.present? is false
  • validate the absence of a boolean field you should use validates :field_name, exclusion: { in: [true, false] }.
  • validates that the attribute's value is unique right before the object gets saved
  • a :scope option that you can use to specify other attributes that are used to limit the uniqueness check
  • a :case_sensitive option that you can use to define whether the uniqueness constraint will be case sensitive or not.
  • There is no default error message for validates_with.
  • To implement the validate method, you must have a record parameter defined, which is the record to be validated.
  • the validator will be initialized only once for the whole application life cycle, and not on each validation run, so be careful about using instance variables inside it.
  • passes the record to a separate class for validation
  • use a plain old Ruby object
  • validates attributes against a block
  • The block receives the record, the attribute's name and the attribute's value. You can do anything you like to check for valid data within the block
  • will let validation pass if the attribute's value is blank?, like nil or an empty string
  • the :message option lets you specify the message that will be added to the errors collection when validation fails
  • skips the validation when the value being validated is nil
  • specify when the validation should happen
  • raise ActiveModel::StrictValidationFailed when the object is invalid
  • You can do that by using the :if and :unless options, which can take a symbol, a string, a Proc or an Array.
  • use the :if option when you want to specify when the validation should happen
  • using eval and needs to contain valid Ruby code.
  • Using a Proc object gives you the ability to write an inline condition instead of a separate method
  • have multiple validations use one condition, it can be easily achieved using with_options.
  • implement a validate method which takes a record as an argument and performs the validation on it
  • validates_with method
  • implement a validate_each method which takes three arguments: record, attribute, and value
  • combine standard validations with your own custom validators.
  • :expiration_date_cannot_be_in_the_past,    :discount_cannot_be_greater_than_total_value
  • By default such validations will run every time you call valid?
  • errors[] is used when you want to check the error messages for a specific attribute.
  • Returns an instance of the class ActiveModel::Errors containing all errors.
  • lets you manually add messages that are related to particular attributes
  • using []= setter
  • errors[:base] is an array, you can simply add a string to it and it will be used as an error message.
  • use this method when you want to say that the object is invalid, no matter the values of its attributes.
  • clear all the messages in the errors collection
  • calling errors.clear upon an invalid object won't actually make it valid: the errors collection will now be empty, but the next time you call valid? or any method that tries to save this object to the database, the validations will run again.
  • the total number of error messages for the object.
  • .errors.full_messages.each
  • .field_with_errors
張 旭

Understanding Polymorphic Associations in Rails - 0 views

  • STI provides you with more flexibility than polymorphic association but we have to create separate classes to implement the associations.
  • need has_many :through with polymorphic association
  • inverse_of: does not work with polymorphic associations.
  • ...3 more annotations...
  • with polymorphic associations, a model can belong to more than one other model, on a single association
  • taking care of polymorphic association
  • STI adds lot more code and can be difficult to implement compared to polymorphic association.
張 旭

plataformatec/simple_form - 0 views

  • The basic goal of Simple Form is to not touch your way of defining the layout
  • by default contains label, hints, errors and the input itself
  • Simple Form acts as a DSL and just maps your input type (retrieved from the column definition in the database) to a specific helper method.
  • ...68 more annotations...
  • can overwrite the default label by passing it to the input method
  • configure the html of any of them
  • disable labels, hints or error
  • add a hint, an error, or even a placeholder
  • add an inline label
  • pass any html attribute straight to the input, by using the :input_html option
  • use the :defaults option in simple_form_fo
  • Simple Form generates a wrapper div around your label and input by default, you can pass any html attribute to that wrapper as well using the :wrapper_html option,
  • By default all inputs are required
  • the required property of any input can be overwritten
  • Simple Form will look at the column type in the database and use an appropriate input for the column
  • lets you overwrite the default input type it creates
  • can also render boolean attributes using as: :select to show a dropdown.
  • give the :disabled option to Simple Form, and it'll automatically mark the wrapper as disabled with a CSS class
  • Simple Form accepts same options as their corresponding input type helper in Rails
  • Any extra option passed to these methods will be rendered as html option.
  • use label, hint, input_field, error and full_error helpers
  • to strip away all the div wrappers around the <input> field
  • is to use f.input_field
  • changing boolean_style from default value :nested to :inline
  • overriding the :collection option
  • Collections can be arrays or ranges, and when a :collection is given the :select input will be rendered by default
  • Other types of collection are :radio_buttons and :check_boxes
  • label_method
  • value_method
  • Both of these options also accept lambda/procs
  • define a to_label method on your model as Simple Form will search for and use :to_label as a :label_method first if it is found
  • create grouped collection selects, that will use the html optgroup tags
  • Grouped collection inputs accept the same :label_method and :value_method options
  • group_method
  • group_label_method
  • configured with a default value to be used on the site through the SimpleForm.country_priority and SimpleForm.time_zone_priority helpers.
  • association
  • association
  • render a :select input for choosing the :company, and another :select input with :multiple option for the :roles
  • all options available to :select, :radio_buttons and :check_boxes are also available to association
  • declare different labels and values
  • the association helper is currently only tested with Active Record
  • f.input
  • f.select
  • create a <button> element
  • simple_fields_for
  • Creates a collection of radio inputs with labels associated
  • Creates a collection of checkboxes with labels associated
  • collection_radio_buttons
  • collection_check_boxes
  • associations in your model
  • Role.all
  • the html element you will get for each attribute according to its database definition
  • redefine existing Simple Form inputs by creating a new class with the same name
  • Simple Form uses all power of I18n API to lookup labels, hints, prompts and placeholders
  • specify defaults for all models under the 'defaults' key
  • Simple Form will always look for a default attribute translation under the "defaults" key if no specific is found inside the model key
  • Simple Form will fallback to default human_attribute_name from Rails when no other translation is found for labels.
  • Simple Form will only do the lookup for options if you give a collection composed of symbols only.
  • "Add %{model}"
  • translations for labels, hints and placeholders for a namespaced model, e.g. Admin::User, should be placed under admin_user, not under admin/user
  • This difference exists because Simple Form relies on object_name provided by Rails' FormBuilder to determine the translation path for a given object instead of i18n_key from the object itself.
  • configure how your components will be rendered using the wrappers API
  • optional
  • unless_blank
  • By default, Simple Form will generate input field types and attributes that are supported in HTML5
  • The HTML5 extensions include the new field types such as email, number, search, url, tel, and the new attributes such as required, autofocus, maxlength, min, max, step.
  • If you want to have all other HTML 5 features, such as the new field types, you can disable only the browser validation
  • add novalidate to a specific form by setting the option on the form itself
  • the Simple Form configuration file
  • passing the html5 option
  • as: :date, html5: true
張 旭

Using Traefik as a reverse proxy | Blog Eleven Labs - 0 views

  • a proxy is associated with the client(s), while a reverse proxy is associated with the server(s); a reverse proxy is usually an internal-facing proxy used as a ‘front-end’ to control and protect access to a server on a private network.
  • the restart: always instruction will allow our reverse-proxy service to restart automatically, on its own.
  • add an [api] section to enable the dashboard and the API
  • ...6 more annotations...
  • double the $ symbols in order to escape the $ symbols as it tries to reference a variable.
  • stay consistent with names inside routers and middlewares.
  • providers.file
  • the service name is always in the form of [service name]@[provider
  • write different routing rules for a service and how to generate SSL certificates
  • traefik.http.services.home.loadbalancer.server.port=8123 indicates that the service port I want to expose is 8123.
  •  
    "a proxy is associated with the client(s), while a reverse proxy is associated with the server(s); a reverse proxy is usually an internal-facing proxy used as a 'front-end' to control and protect access to a server on a private network."
張 旭

Internet Gateways - Amazon Virtual Private Cloud - 0 views

  • to provide a target in your VPC route tables for internet-routable traffic
  • to perform network address translation (NAT) for instances that have been assigned public IPv4 addresses
  • Ensure that instances in your subnet have a globally unique IP address (public IPv4 address, Elastic IP address, or IPv6 address)
  • ...10 more annotations...
  • To use an internet gateway, your subnet's route table must contain a route that directs internet-bound traffic to the internet gateway.
  • If your subnet is associated with a route table that has a route to an internet gateway, it's known as a public subnet.
  • To enable communication over the internet for IPv4, your instance must have a public IPv4 address or an Elastic IP address that's associated with a private IPv4 address on your instance.
  • Your instance is only aware of the private (internal) IP address space defined within the VPC and subnet
  • internet gateway logically provides the one-to-one NAT on behalf of your instance
  • To enable communication over the internet for IPv6, your VPC and subnet must have an associated IPv6 CIDR block, and your instance must be assigned an IPv6 address from the range of the subnet.
  • When you create a subnet, we automatically associate it with the main route table for the VPC.
  • the main route table doesn't contain a route to an internet gateway
  • Each instance that you launch into a VPC is automatically associated with its default security group.
  • a default security group allow no inbound traffic from the internet and allow all outbound traffic to the internet.
crazylion lee

Realtime Multi-Person 2D Pose Estimation using Part Affinity Fields - 0 views

  •  
    "We present a realtime approach for multi-person 2D pose estimation that predicts vector fields, which we refer to as Part Affinity Fields (PAFs), that directly expose the association between anatomical parts in an image. The architecture is designed to jointly learn part locations and their association, via two branches of the same sequential prediction process."
張 旭

The Flatiron School | Why You Don't Need Has_and_belongs_to_many... - 0 views

  • When creating associations between models, you almost never know how this relationship will blossom as your application grows.
  • setup a solid has_many :through relationship with an associated join table, you provide yourself with a huge amount of flexibility down the road.
  • A has_many :through association is used to setup a many to many relationship with another model
  • ...2 more annotations...
  • This relationship now allows for extending the association within the join table.
  • You should use has_many :through if you need validations, callbacks, or extra attributes on the join model
張 旭

VPCs and Subnets - Amazon Virtual Private Cloud - 0 views

  • you must specify a range of IPv4 addresses for the VPC in the form of a Classless Inter-Domain Routing (CIDR) block
  • A VPC spans all the Availability Zones in the region
  • add one or more subnets in each Availability Zone.
  • ...19 more annotations...
  • Each subnet must reside entirely within one Availability Zone and cannot span zones.
  • Availability Zones are distinct locations that are engineered to be isolated from failures in other Availability Zones
  • If a subnet's traffic is routed to an internet gateway, the subnet is known as a public subnet.
  • If a subnet doesn't have a route to the internet gateway, the subnet is known as a private subnet.
  • If a subnet doesn't have a route to the internet gateway, but has its traffic routed to a virtual private gateway for a VPN connection, the subnet is known as a VPN-only subnet.
  • By default, all VPCs and subnets must have IPv4 CIDR blocks—you can't change this behavior.
  • The allowed block size is between a /16 netmask (65,536 IP addresses) and /28 netmask (16 IP addresses).
  • The first four IP addresses and the last IP address in each subnet CIDR block are not available for you to use
  • The allowed block size is between a /28 netmask and /16 netmask
  • The CIDR block must not overlap with any existing CIDR block that's associated with the VPC.
  • Each subnet must be associated with a route table
  • Every subnet that you create is automatically associated with the main route table for the VPC
  • Security groups control inbound and outbound traffic for your instances
  • network ACLs control inbound and outbound traffic for your subnets
  • each subnet must be associated with a network ACL
  • You can create a flow log on your VPC or subnet to capture the traffic that flows to and from the network interfaces in your VPC or subnet.
  • A VPC peering connection enables you to route traffic between the VPCs using private IP addresses
  • you cannot create a VPC peering connection between VPCs that have overlapping CIDR blocks
  • recommend that you create a VPC with a CIDR range large enough for expected future growth, but not one that overlaps with current or expected future subnets anywhere in your corporate or home network, or that overlaps with current or future VPCs
張 旭

Getting Started with Rails - Ruby on Rails Guides - 0 views

  • A controller's purpose is to receive specific requests for the application.
  • Routing decides which controller receives which requests
  • The view should just display that information
  • ...55 more annotations...
  • view templates are written in a language called ERB (Embedded Ruby) which is converted by the request cycle in Rails before being sent to the user.
  • Each action's purpose is to collect information to provide it to a view.
  • A view's purpose is to display this information in a human readable format.
  • routing file which holds entries in a special DSL (domain-specific language) that tells Rails how to connect incoming requests to controllers and actions.
  • You can create, read, update and destroy items for a resource and these operations are referred to as CRUD operations
  • A controller is simply a class that is defined to inherit from ApplicationController.
  • If not found, then it will attempt to load a template called application/new. It looks for one here because the PostsController inherits from ApplicationController
  • :formats specifies the format of template to be served in response. The default format is :html, and so Rails is looking for an HTML template.
  • :handlers, is telling us what template handlers could be used to render our template.
  • When you call form_for, you pass it an identifying object for this form. In this case, it's the symbol :post. This tells the form_for helper what this form is for.
  • that the action attribute for the form is pointing at /posts/new
  • When a form is submitted, the fields of the form are sent to Rails as parameters.
  • parameters can then be referenced inside the controller actions, typically to perform a particular task
  • params method is the object which represents the parameters (or fields) coming in from the form.
  • Active Record is smart enough to automatically map column names to model attributes,
  • Rails uses rake commands to run migrations, and it's possible to undo a migration after it's been applied to your database
  • every Rails model can be initialized with its respective attributes, which are automatically mapped to the respective database columns.
  • migration creates a method named change which will be called when you run this migration.
  • The action defined in this method is also reversible, which means Rails knows how to reverse the change made by this migration, in case you want to reverse it later
  • Migration filenames include a timestamp to ensure that they're processed in the order that they were created.
  • @post.save returns a boolean indicating whether the model was saved or not.
  • prevents an attacker from setting the model's attributes by manipulating the hash passed to the model.
  • If you want to link to an action in the same controller, you don't need to specify the :controller option, as Rails will use the current controller by default.
  • inherits from ActiveRecord::Base
  • Active Record supplies a great deal of functionality to your Rails models for free, including basic database CRUD (Create, Read, Update, Destroy) operations, data validation, as well as sophisticated search support and the ability to relate multiple models to one another.
  • Rails includes methods to help you validate the data that you send to models
  • Rails can validate a variety of conditions in a model, including the presence or uniqueness of columns, their format, and the existence of associated objects.
  • redirect_to will tell the browser to issue another request.
  • rendering is done within the same request as the form submission
  • Each request for a comment has to keep track of the post to which the comment is attached, thus the initial call to the find method of the Post model to get the post in question.
  • pluralize is a rails helper that takes a number and a string as its arguments. If the number is greater than one, the string will be automatically pluralized.
  • The render method is used so that the @post object is passed back to the new template when it is rendered.
  • The method: :patch option tells Rails that we want this form to be submitted via the PATCH HTTP method which is the HTTP method you're expected to use to update resources according to the REST protocol.
  • it accepts a hash containing the attributes that you want to update.
  • field_with_errors. You can define a css rule to make them standout
  • belongs_to :post, which sets up an Active Record association
  • creates comments as a nested resource within posts
  • call destroy on Active Record objects when you want to delete them from the database.
  • Rails allows you to use the dependent option of an association to achieve this.
  • store all external data as UTF-8
  • you're better off ensuring that all external data is UTF-8
  • use UTF-8 as the internal storage of your database
  • Rails defaults to converting data from your database into UTF-8 at the boundary.
  • :patch
  • By default forms built with the form_for helper are sent via POST
  • The :method and :'data-confirm' options are used as HTML5 attributes so that when the link is clicked, Rails will first show a confirm dialog to the user, and then submit the link with method delete. This is done via the JavaScript file jquery_ujs which is automatically included into your application's layout (app/views/layouts/application.html.erb) when you generated the application.
  • Without this file, the confirmation dialog box wouldn't appear.
  • just defines the partial template we want to render
  • As the render method iterates over the @post.comments collection, it assigns each comment to
  • a local variable named the same as the partial
  • use the authentication system
  • require and permit
  • the method is often made private to make sure it can't be called outside its intended context.
  • standard CRUD actions in each controller in the following order: index, show, new, edit, create, update and destroy.
  • must be placed before any private or protected method in the controller in order to work
張 旭

NAT Gateways - Amazon Virtual Private Cloud - 0 views

  • a network address translation (NAT) gateway to enable instances in a private subnet to connect to the internet or other AWS services
  • but prevent the internet from initiating a connection with those instances
  • NAT gateways are not supported for IPv6 traffic
  • ...11 more annotations...
  • must specify the public subnet in which the NAT gateway should reside
  • update the route table associated with one or more of your private subnets to point Internet-bound traffic to the NAT gateway.
  • NAT gateway is created in a specific Availability Zone and implemented with redundancy in that zone.
  • ensure that resources use the NAT gateway in the same Availability Zone
  • The main route table sends internet traffic from the instances in the private subnet to the NAT gateway. The NAT gateway sends the traffic to the internet gateway using the NAT gateway’s Elastic IP address as the source IP address
  • A NAT gateway supports 5 Gbps of bandwidth and automatically scales up to 45 Gbps
  • You can associate exactly one Elastic IP address with a NAT gateway
  • A NAT gateway supports the following protocols: TCP, UDP, and ICMP
  • cannot associate a security group with a NAT gateway.
  • create a NAT gateway in the same subnet as your NAT instance, and then replace the existing route in your route table that points to the NAT instance with a route that points to the NAT gateway
  • A NAT gateway cannot send traffic over VPC endpoints, VPN connections, AWS Direct Connect, or VPC peering connections.
crazylion lee

Machine Learning for Everyday Tasks - 0 views

  •  
    "Machine learning is often thought to be too complicated for everyday development tasks. We often associate it with things like big data, data mining, data science, and artificial intelligence. Sometimes it feels something like this:"
張 旭

Break Deep Associations - 0 views

  • 常寫單元測試的開發者,多半已經養成遇到難測的元件時,就替該元件抽一個 interface 隔離
  • 部署的時候再藉由 Dependency Injection 注入真正的實作
  • 將它們隔離。這跟 class 抽 interface 其實很像的,都讓耦合下降,提高模組化
  • ...1 more annotation...
  • 如果測試很難寫,那八成設計有問題
張 旭

Active Record Basics - Ruby on Rails Guides - 0 views

  • the model - which is the layer of the system responsible for representing business data and logic.
  • Active Record facilitates the creation and use of business objects whose data requires persistent storage to a database
  • Rails will pluralize your class names to find the respective database table.
  • ...33 more annotations...
  • objects carry both persistent data and behavior which operates on that data
  • Object-Relational Mapping, commonly referred to as its abbreviation ORM, is a technique that connects the rich objects of an application to tables in a relational database management system
  • Represent associations between these models
  • Validate models before they get persisted to the database
  • The idea is that if you configure your applications in the very same way most of the times then this should be the default way.
  • Database Table - Plural with underscores separating words
  • use the ActiveRecord::Base.table_name= method to specify the table name
  • Model Class - Singular with the first letter of each word capitalized
  • Foreign keys - These fields should be named following the pattern singularized_table_name_id
  • Primary keys - By default, Active Record will use an integer column named id as the table's primary key
  • created_at
  • updated_at
  • (table_name)_count - Used to cache the number of belonging objects on associations.
  • Single Table Inheritance (STI)
  • Object Relational Mapping
  • class_name.yml
  • ActiveRecord::Base.primary_key=
  • CRUD is an acronym for the four verbs we use to operate on data: Create, Read, Update and Delete.
  • new method will return a new object
  • create will return the object and save it to the database.
  • Using the new method, an object can be instantiated without being saved
  • user.save will commit the record to the database
  • update_all class method
  • an Active Record object can be destroyed which removes it from the database
  • Validation is a very important issue to consider when persisting to database, so the methods create, save and update take it into account when running: they return false when validation fails and they didn't actually perform any operation on database.
  • a bang counterpart
  • Active Record callbacks allow you to attach code to certain events in the life-cycle of your models
  • Rails keeps track of which files have been committed to the database and provides rollback features
  • rake db:migrate
  • rake db:rollback
  • Convention over Configuration
    • 張 旭
       
      Model 是單數,Table 是複數。想象一下,處理 Object 的時候是逐一處理,但是存放的地方是放了一堆 Objects。
    • 張 旭
       
      外鍵是單數的形式,這也很好理解:因為關聯到的是一個外部的 Object
張 旭

Outbound connections in Azure | Microsoft Docs - 0 views

  • When an instance initiates an outbound flow to a destination in the public IP address space, Azure dynamically maps the private IP address to a public IP address.
  • After this mapping is created, return traffic for this outbound originated flow can also reach the private IP address where the flow originated.
  • Azure uses source network address translation (SNAT) to perform this function
  • ...22 more annotations...
  • When multiple private IP addresses are masquerading behind a single public IP address, Azure uses port address translation (PAT) to masquerade private IP addresses.
  • If you want outbound connectivity when working with Standard SKUs, you must explicitly define it either with Standard Public IP addresses or Standard public Load Balancer.
  • the VM is part of a public Load Balancer backend pool. The VM does not have a public IP address assigned to it.
  • The Load Balancer resource must be configured with a load balancer rule to create a link between the public IP frontend with the backend pool.
  • VM has an Instance Level Public IP (ILPIP) assigned to it. As far as outbound connections are concerned, it doesn't matter whether the VM is load balanced or not.
  • When an ILPIP is used, the VM uses the ILPIP for all outbound flows.
  • A public IP assigned to a VM is a 1:1 relationship (rather than 1: many) and implemented as a stateless 1:1 NAT.
  • Port masquerading (PAT) is not used, and the VM has all ephemeral ports available for use.
  • When the load-balanced VM creates an outbound flow, Azure translates the private source IP address of the outbound flow to the public IP address of the public Load Balancer frontend.
  • Azure uses SNAT to perform this function. Azure also uses PAT to masquerade multiple private IP addresses behind a public IP address.
  • Ephemeral ports of the load balancer's public IP address frontend are used to distinguish individual flows originated by the VM.
  • When multiple public IP addresses are associated with Load Balancer Basic, any of these public IP addresses are a candidate for outbound flows, and one is selected at random.
  • the VM is not part of a public Load Balancer pool (and not part of an internal Standard Load Balancer pool) and does not have an ILPIP address assigned to it.
  • The public IP address used for this outbound flow is not configurable and does not count against the subscription's public IP resource limit.
  • Do not use this scenario for whitelisting IP addresses.
  • This public IP address does not belong to you and cannot be reserved.
  • Standard Load Balancer uses all candidates for outbound flows at the same time when multiple (public) IP frontends is present.
  • Load Balancer Basic chooses a single frontend to be used for outbound flows when multiple (public) IP frontends are candidates for outbound flows.
  • the disableOutboundSnat option defaults to false and signifies that this rule programs outbound SNAT for the associated VMs in the backend pool of the load balancing rule.
  • Port masquerading SNAT (PAT)
  • Ephemeral port preallocation for port masquerading SNAT (PAT)
  • determine the public source IP address of an outbound connection.
張 旭

Serverless Architectures - 0 views

  • Serverless was first used to describe applications that significantly or fully depend on 3rd party applications / services (‘in the cloud’) to manage server-side logic and state.
  • ‘rich client’ applications (think single page web apps, or mobile apps) that use the vast ecosystem of cloud accessible databases (like Parse, Firebase), authentication services (Auth0, AWS Cognito), etc.
  • ‘(Mobile) Backend as a Service’
  • ...33 more annotations...
  • Serverless can also mean applications where some amount of server-side logic is still written by the application developer but unlike traditional architectures is run in stateless compute containers that are event-triggered, ephemeral (may only last for one invocation), and fully managed by a 3rd party.
  • ‘Functions as a service
  • AWS Lambda is one of the most popular implementations of FaaS at present,
  • A good example is Auth0 - they started initially with BaaS ‘Authentication as a Service’, but with Auth0 Webtask they are entering the FaaS space.
  • a typical ecommerce app
  • a backend data-processing service
  • with zero administration.
  • FaaS offerings do not require coding to a specific framework or library.
  • Horizontal scaling is completely automatic, elastic, and managed by the provider
  • Functions in FaaS are triggered by event types defined by the provider.
  • a FaaS-supported message broker
  • from a deployment-unit point of view FaaS functions are stateless.
  • allowed the client direct access to a subset of our database
  • deleted the authentication logic in the original application and have replaced it with a third party BaaS service
  • The client is in fact well on its way to becoming a Single Page Application.
  • implement a FaaS function that responds to http requests via an API Gateway
  • port the search code from the Pet Store server to the Pet Store Search function
  • replaced a long lived consumer application with a FaaS function that runs within the event driven context
  • server applications - is a key difference when comparing with other modern architectural trends like containers and PaaS
  • the only code that needs to change when moving to FaaS is the ‘main method / startup’ code, in that it is deleted, and likely the specific code that is the top-level message handler (the ‘message listener interface’ implementation), but this might only be a change in method signature
  • With FaaS you need to write the function ahead of time to assume parallelism
  • Most providers also allow functions to be triggered as a response to inbound http requests, typically in some kind of API gateway
  • you should assume that for any given invocation of a function none of the in-process or host state that you create will be available to any subsequent invocation.
  • FaaS functions are either naturally stateless
  • store state across requests or for further input to handle a request.
  • certain classes of long lived task are not suited to FaaS functions without re-architecture
  • if you were writing a low-latency trading application you probably wouldn’t want to use FaaS systems at this time
  • An API Gateway is an HTTP server where routes / endpoints are defined in configuration and each route is associated with a FaaS function.
  • API Gateway will allow mapping from http request parameters to inputs arguments for the FaaS function
  • API Gateways may also perform authentication, input validation, response code mapping, etc.
  • the Serverless Framework makes working with API Gateway + Lambda significantly easier than using the first principles provided by AWS.
  • Apex - a project to ‘Build, deploy, and manage AWS Lambda functions with ease.'
  • 'Serverless' to mean the union of a couple of other ideas - 'Backend as a Service' and 'Functions as a Service'.
張 旭

Probably Done Before: Visualizing Docker Containers and Images - 0 views

  •  In my opinion, understanding how a technology works under the hood is the best way to achieve learning speed and to build confidence that you are using the tool in the correct way.
  • union view
    • 張 旭
       
      把多層 image layer 串接起來,看上去就像是在讀一個 image 檔案而已。
  • The top-level layer may be read by a union-ing file system (AUFS on my docker implementation) to present a single cohesive view of all the changes as one read-only file system
  • ...36 more annotations...
  • it is nearly the same thing as an image, except that the top layer is read-write
  • A container is defined only as a read-write layer atop an image (of read-only layers itself).  It does not have to be running.
  • a running container
    • 張 旭
       
      之前一直搞錯了!不是 run 起來的才會叫 container,只要有 read-write layer 就是了!
  • the the isolated process-space and processes within
  • A running container is defined as a read-write "union view" and
  • kernel-level technologies like cgroups, namespaces
  • The processes within this process-space may change, delete or create files within the "union view" file that will be captured in the read-write layer
  • there is no longer a running container
    • 張 旭
       
      這行指令執行結束之後,running container 就停掉了,但是該 container 還在!
  • each layer contains a pointer to a parent layer using the Id
  • The 'docker create' command adds a read-write layer to the top stack based on the image id.  It does not run this container.
  • The command 'docker start' creates a process space around the union view of the container's layers.
  • can only be one process space per container.
  • the docker run command starts with an image, creates a container, and starts the container
  • 'git pull' (which is a combination of 'git fetch' and 'git merge')
  • 'docker ps' lists out the inventory of running containers on your system
  • 'docker ps -a' where the 'a' is short for 'all' lists out all the containers on your system, whether stopped or running.
  • Only those images that have containers attached to them or that have been pulled are considered top-level.
  • 'docker stop' issues a SIGTERM to a running container which politely stops all the processes in that process-space.
  • results is a normal, but non-running, container
  • 'docker kill' issues a non-polite SIGKILL command to all the processes in a running container.
  • 'docker stop' and 'docker kill' which send actual UNIX signals to a running process
  • 'docker pause' uses a special cgroups feature to freeze/pause a running process-space
  • 'docker rm' removes the read-write layer that defines a container from your host system
  • It effectively deletes files
  • 'docker rmi' removes the read-layer that defines a "union view" of an image.
  • 'docker commit' takes a container's top-level read-write layer and burns it into a read-only layer.
  • turns a container (whether running or stopped) into an immutable image
  • uses the FROM directive in the Dockerfile file as the starting image and iteratively 1) runs (create and start) 2) modifies and 3) commits.
  • At each step in the iteration a new layer is created.
  • 'docker exec' command runs on a running container and executes a process in that running container's process space
  • 'docker inspect' fetches the metadata that has been associated with the top-layer of the container or image
  • 'docker save' creates a single tar file that can be used to import on a different host system
  • only be run on an image
  • 'docker export' command creates a tar file of the contents of the "union view" and flattens it for consumption for non-Docker usages
  • This command removes the metadata and the layers.  This command can only be run on containers.
  • 'docker history' command takes an image-id and recursively prints out the read-only layers
張 旭

rails/activeresource - 0 views

    • 張 旭
       
      所以執行 Person.find 時,會發送一個 GET 到 api.people.com:3000
    • 張 旭
       
      所以執行 Person.find 時,會發送一個 GET 到 api.people.com:3000
  • Active Resource is built on a standard JSON or XML format for requesting and submitting resources over HTTP
  • REST uses HTTP, but unlike “typical” web applications, it makes use of all the verbs available in the HTTP specification
  • ...2 more annotations...
  • When a request is made to a remote resource, a REST JSON request is generated, transmitted, and the result received and serialized into a usable Ruby object.
  • Relationships between resources can be declared using the standard association syntax that should be familiar to anyone who uses activerecord
張 旭

Docker Explained: Using Dockerfiles to Automate Building of Images | DigitalOcean - 0 views

  • CMD would be running an application upon creation of a container which is already installed using RUN (e.g. RUN apt-get install …) inside the image
  • ENTRYPOINT argument sets the concrete default application that is used every time a container is created using the image.
  • ENV command is used to set the environment variables (one or more).
  • ...6 more annotations...
  • EXPOSE command is used to associate a specified port to enable networking between the running process inside the container and the outside world
  • defines the base image to use to start the build process
  • Unlike CMD, it actually is used to build the image (forming another layer on top of the previous one which is committed).
  • VOLUME command is used to enable access from your container to a directory on the host machine
  • set where the command defined with CMD is to be executed
  • To detach yourself from the container, use the escape sequence CTRL+P followed by CTRL+Q
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