Group items tagged

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.

allowing your schema and changes to be database independent.

each migration as being a new 'version' of the database

each migration modifies it to add or remove tables, columns, or entries

roll this migration back, it will remove the table

timestamps macro adds two columns, created_at and updated_at

On databases that support transactions with statements that change the schema, migrations are wrapped in a transaction

reversible

use up and down instead of change

Migrations are stored as files in the db/migrate directory, one for each migration class.

a UTC timestamp identifying

Rails uses this timestamp to determine which migration should be run and in what order

"AddXXXToYYY" or "RemoveXXXFromYYY"

use a Ruby DSL

column type as references

part_number:string:index

a migration to remove a column

"CreateXXX"

change_column_null

AddUserRefToProducts

:references

produce join tables if JoinTable is part of the name

CreateJoinTable

The model and scaffold generators will create migrations appropriate for adding a new model.

enclosed by curly braces and follow the field type

create_table

By default, create_table will create a primary key called id

add an index on the new column

when using MySQL, the default is ENGINE=InnoDB

create_join_table creates an HABTM (has and belongs to many) join table

create_join_table also accepts a block

change_table, used for changing existing tables

remove

rename

add_column

change_column

remove_column

change_column_default

place an SQL fragment in the :options option.

limit

precision

scale

polymorphic

default

index

add_foreign_key

use the old style of migration using up and down methods instead of the change method.

.connection.execute

remove_column is reversible if you supply the column type as the third argument

Complex migrations may require processing that Active Record doesn't know how to reverse

reversible

Using reversible will ensure that the instructions are executed in the right order too.

add_column add_foreign_key add_index add_reference add_timestamps change_column_default (must supply a :from and :to option) change_column_null create_join_table create_table disable_extension drop_join_table drop_table (must supply a block) enable_extension remove_column (must supply a type) remove_foreign_key (must supply a second table) remove_index remove_reference remove_timestamps rename_column rename_index rename_table

:column_options option

have the option :null set to false by default

By default, the name of the join table comes from the union of the first two arguments provided to create_join_table

If the column names can not be derived from the table names, you can use the :column and :primary_key options.

figure out the column name

foreign key for a specific column

foreign key by name

should use reversible or write the up and down methods instead of using the change method

If your migration is irreversible, you should raise ActiveRecord::IrreversibleMigration from your down method.

DontUseConstraintForZipcodeValidationMigration

rails db:migrate

specify a target version

all migrations up to and including 20080906120000

run the down method on all the migrations down to, but not including, 20080906120000

rails db:rollback

db:migrate:redo task is a shortcut for doing a rollback and then migrating back up again

STEP parameter

db:setup task will create the database, load the schema and initialize it with the seed data

db:reset task will drop the database and set it up again. This is functionally equivalent to rails db:drop db:setup.

run a specific migration up or down, the db:migrate:up and db:migrate:down

the RAILS_ENV environment variable

db:migrate VERBOSE=false will suppress all output.

must rollback the migration (for example with bin/rails db:rollback), edit your migration and then run rails db:migrate to run the corrected version.

editing existing migrations is not a good idea.

revert method can be helpful when writing a new migration to undo previous migrations in whole or in part

require_relative

revert

Schema Files for

Schema files are also useful if you want a quick look at what attributes an Active Record object has

annotate_models gem automatically adds and updates comments at the top of each model summarizing the schema if you desire that functionality.

database-independent

multiple databases

you can execute custom SQL statements, the schema dumper cannot reconstitute those statements from the database

db:structure:dump

set in config/application.rb by the config.active_record.schema_format setting, which may be either :sql or :ruby.

check them into source control.

db/schema.rb contains the current version number of the database

Validations such as validates :foreign_key, uniqueness: true are one way in which models can enforce data integrity

The :dependent option on associations allows models to automatically destroy child objects when the parent is destroyed.

Migrations can also be used to add or modify data

Initial

To add initial data after a database is created, Rails has a built-in 'seeds' feature that makes the process quick and easy.

db/seeds.rb

rails db:seed

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

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.

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

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.

{% ... %} for Statements

{{ ... }} for Expressions to print to the template output

use a dot (.) to access attributes of a variable

the outer double-curly braces are not part of the variable, but the print statement.

if an object has an item and attribute with the same name. Additionally, the attr() filter only looks up attributes.

Variables can be modified by filters. Filters are separated from the variable by a pipe symbol (|) and may have optional arguments in parentheses.

Multiple filters can be chained

Tests can be used to test a variable against a common expression.

add is plus the name of the test after the variable.

to find out if a variable is defined, you can do name is defined, which will then return true or false depending on whether name is defined in the current template context.

strip whitespace in templates by hand. If you add a minus sign (-) to the start or end of a block (e.g. a For tag), a comment, or a variable expression, the whitespaces before or after that block will be removed

not add whitespace between the tag and the minus sign

mark a block raw

Template inheritance allows you to build a base “skeleton” template that contains all the common elements of your site and defines blocks that child templates can override.

The {% extends %} tag is the key here. It tells the template engine that this template “extends” another template.

access templates in subdirectories with a slash

can’t define multiple {% block %} tags with the same name in the same template

put the name of the block after the end tag for better readability

if the block is replaced by a child template, a variable would appear that was not defined in the block or passed to the context.

setting the block to “scoped” by adding the scoped modifier to a block declaration

Jinja2 functions (macros, super, self.BLOCKNAME) always return template data that is marked as safe.

With the default syntax, control structures appear inside {% ... %} blocks.

the dictsort filter

loop.cycle

use loops recursively

whether the value changed at all,

use it to test if a variable is defined, not empty and not false

Macros are comparable with functions in regular programming languages.

If a macro name starts with an underscore, it’s not exported and can’t be imported.

pass a macro to another macro

caller()

a single trailing newline is stripped if present

other whitespace (spaces, tabs, newlines etc.) is returned unchanged

caller(user)

call(user)

This is a simple dialog rendered by using a macro and a call block.

Filter sections allow you to apply regular Jinja2 filters on a block of template data.

Assignments at top level (outside of blocks, macros or loops) are exported from the template like top level macros and can be imported by other templates.

using namespace objects which allow propagating of changes across scopes

use block assignments to capture the contents of a block into a variable name.

The extends tag can be used to extend one template from another.

Blocks are used for inheritance and act as both placeholders and replacements at the same time.

The include statement is useful to include a template and return the rendered contents of that file into the current namespace

Included templates have access to the variables of the active context by default.

putting often used code into macros

imports are cached and imported templates don’t have access to the current template variables, just the globals by default.

Macros and variables starting with one or more underscores are private and cannot be imported.

By default, included templates are passed the current context and imported templates are not.

Integers and floating point numbers are created by just writing the number down

Everything between two brackets is a list.

Tuples are like lists that cannot be modified (“immutable”).

A dict in Python is a structure that combines keys and values.

// Divide two numbers and return the truncated integer result

(expr) group an expression.

The is and in operators support negation using an infix notation

in Perform a sequence / mapping containment test.

| Applies a filter.

~ Converts all operands into strings and concatenates them.

use inline if expressions.

always an attribute is returned and items are not looked up.

default(value, default_value=u'', boolean=False)¶ If the value is undefined it will return the passed default value, otherwise the value of the variable

dictsort(value, case_sensitive=False, by='key', reverse=False)¶ Sort a dict and yield (key, value) pairs.

format(value, *args, **kwargs)¶ Apply python string formatting on an object

indent(s, width=4, first=False, blank=False, indentfirst=None)¶ Return a copy of the string with each line indented by 4 spaces. The first line and blank lines are not indented by default.

join(value, d=u'', attribute=None)¶ Return a string which is the concatenation of the strings in the sequence.

map()¶ Applies a filter on a sequence of objects or looks up an attribute.

pprint(value, verbose=False)¶ Pretty print a variable. Useful for debugging.

reject()¶ Filters a sequence of objects by applying a test to each object, and rejecting the objects with the test succeeding.

replace(s, old, new, count=None)¶ Return a copy of the value with all occurrences of a substring replaced with a new one.

round(value, precision=0, method='common')¶ Round the number to a given precision

even if rounded to 0 precision, a float is returned.

select()¶ Filters a sequence of objects by applying a test to each object, and only selecting the objects with the test succeeding.

sort(value, reverse=False, case_sensitive=False, attribute=None)¶ Sort an iterable. Per default it sorts ascending, if you pass it true as first argument it will reverse the sorting.

striptags(value)¶ Strip SGML/XML tags and replace adjacent whitespace by one space.

tojson(value, indent=None)¶ Dumps a structure to JSON so that it’s safe to use in <script> tags.

trim(value)¶ Strip leading and trailing whitespace.

unique(value, case_sensitive=False, attribute=None)¶ Returns a list of unique items from the the given iterable

urlize(value, trim_url_limit=None, nofollow=False, target=None, rel=None)¶ Converts URLs in plain text into clickable links.

defined(value)¶ Return true if the variable is defined

in(value, seq)¶ Check if value is in seq.

mapping(value)¶ Return true if the object is a mapping (dict etc.).

number(value)¶ Return true if the variable is a number.

sameas(value, other)¶ Check if an object points to the same memory address than another object

undefined(value)¶ Like defined() but the other way round.

A joiner is passed a string and will return that string every time it’s called, except the first time (in which case it returns an empty string).

namespace(...)¶ Creates a new container that allows attribute assignment using the {% set %} tag

The with statement makes it possible to create a new inner scope. Variables set within this scope are not visible outside of the scope.

activate and deactivate the autoescaping from within the templates

With both trim_blocks and lstrip_blocks enabled, you can put block tags on their own lines, and the entire block line will be removed when rendered, preserving the whitespace of the contents

nginx template can be used to generate a reverse proxy configuration for docker containers using virtual hosts for routing.

The timestamps macro adds two columns, created_at and updated_at.

A primary key column called id will also be added implicitly, as it's the default primary key for all Active Record models

On databases that support transactions with statements that change the schema, migrations are wrapped in a transaction

AddXXXToYYY

RemoveXXXFromYYY

Migrations are stored as files in the db/migrate directory, one for each migration class

a UTC timestamp identifying the migration followed by an underscore followed by the name of the migration.

The name of the migration class (CamelCased version) should match the latter part of the file name

Rails uses this timestamp to determine which migration should be run and in what order,

Name servers host a domain’s DNS information in a text file called the zone file

Start of Authority (SOA) records

You’ll want to specify at least two name servers. That way, if one of them is down, the next one can continue to serve your DNS information.

Every domain’s zone file contains the admin’s email address, the name servers, and the DNS records.

a zone file, which lists domains and their corresponding IP addresses (and a few other things)

TLD nameserver

ISPs cache a lot of DNS information after they’ve looked it up the first time

Usually caching is a good thing, but it can be a problem if you’ve recently made a change to your DNS information

An A record matches up a domain (or subdomain) to an IP address

point different subdomains to different IP addresses

An AAAA record is just like an A record, but for IPv6 IP addresses.

An AXFR record is a type of DNS record used for DNS replication

used on a slave DNS server to replicate the zone file from a master DNS server

DNS Certification Authority Authorization uses DNS to allow the holder of a domain to specify which certificate authorities are allowed to issue certificates for that domain.

A CNAME record or Canonical Name record matches up a domain (or subdomain) to a different domain.

You should not use a CNAME record for a domain that gets email, because some mail servers handle mail oddly for domains with CNAME records

the target domain for a CNAME record should have a normal A-record resolution

a CNAME record does not function the same way as a URL redirect

A DKIM record or domain keys identified mail record displays the public key for authenticating messages that have been signed with the DKIM protocol

An MX record or mail exchange record sets the mail delivery destination for a domain (or subdomain).

Ideally, an MX record should point to a domain that is also the hostname for its server.

Lower numbers have a higher priority

NS records or name server records set the nameservers for a domain (or subdomain).

You can also set up different nameservers for any of your subdomains.

The order of NS records does not matter; DNS requests are sent randomly to the different servers, and if one host fails to respond, another one will be queried.

A PTR record or pointer record matches up an IP address to a domain (or subdomain), allowing reverse DNS queries to function.

PTR records are usually set with your hosting provider. They are not part of your domain’s zone file.

An SOA record or Start of Authority record labels a zone file with the name of the host where it was originally created.

The administrative email address is written with a period (.) instead of an at symbol (<@>).

The single nameserver mentioned in the SOA record is considered the primary master for the purposes of Dynamic DNS and is the server where zone file changes get made before they are propagated to all other nameservers.

An SPF record or Sender Policy Framework record lists the designated mail servers for a domain (or subdomain).

An SPF record for your domain tells other receiving mail servers which outgoing server(s) are valid sources of email, so they can reject spoofed email from your domain that has originated from unauthorized servers.

Your SPF record will have a domain or subdomain, type (which is TXT, or SPF if your name server supports it), and text (which starts with “v=spf1” and contains the SPF record settings).

An SRV record or service record matches up a specific service that runs on your domain (or subdomain) to a target domain.

A TXT record or text record provides information about the domain in question to other resources on the Internet.

One common use of the TXT record is to create an SPF record on nameservers that don’t natively support SPF.

support multiple virtual hosts for a container

to connect to your backend using HTTPS instead of HTTP, set VIRTUAL_PROTO=https on the backend container.

The contents of /path/to/certs should contain the certificates and private keys for any virtual hosts in use.

to replace the default proxy settings for the nginx container, add a configuration file at /etc/nginx/proxy.conf

The default configuration blocks the Proxy HTTP request header from being sent to downstream servers

add your configuration file under /etc/nginx/conf.d using a name ending in .conf

If your container exposes multiple ports, nginx-proxy will default to the service running on port 80. If you need to specify a different port, you can set a VIRTUAL_PORT env var to select a different one.

To add settings on a per-VIRTUAL_HOST basis, add your configuration file under /etc/nginx/vhost.d

SNI

The default behavior for the proxy when port 80 and 443 are exposed is as follows: If a container has a usable cert, port 80 will redirect to 443 for that container so that HTTPS is always preferred when available. If the container does not have a usable cert, a 503 will be returned.

Name servers host a domain’s DNS information in a text file called a zone file.

Start of Authority (SOA) records

specifying DNS records, which match domain names to IP addresses.

Every domain’s zone file contains the domain administrator’s email address, the name servers, and the DNS records.

Your ISP’s DNS resolver queries a root nameserver for the proper TLD nameserver. In other words, it asks the root nameserver, *Where can I find the nameserver for .com domains?*

In actuality, ISPs cache a lot of DNS information after they’ve looked it up the first time.

An A record points your domain or subdomain to your Linode’s IP address,

use an asterisk (*) as your subdomain

An AAAA record is just like an A record, but for IPv6 IP addresses.

An AXFR record is a type of DNS record used for DNS replication

DNS Certification Authority Authorization uses DNS to allow the holder of a domain to specify which certificate authorities are allowed to issue certificates for that domain.

A CNAME record or Canonical Name record matches a domain or subdomain to a different domain.

Some mail servers handle mail oddly for domains with CNAME records, so you should not use a CNAME record for a domain that gets email.

MX records cannot reference CNAME-defined hostnames.

A DKIM record or DomainKeys Identified Mail record displays the public key for authenticating messages that have been signed with the DKIM protocol

DKIM records are implemented as text records.

An MX record or mail exchanger record sets the mail delivery destination for a domain or subdomain.

An MX record should ideally point to a domain that is also the hostname for its server.

Priority allows you to designate a fallback server (or servers) for mail for a particular domain. Lower numbers have a higher priority.

NS records or name server records set the nameservers for a domain or subdomain.

You can also set up different nameservers for any of your subdomains

Primary nameservers get configured at your registrar and secondary subdomain nameservers get configured in the primary domain’s zone file.

A PTR record or pointer record matches up an IP address to a domain or subdomain, allowing reverse DNS queries to function.

opposite service an A record does

PTR records are usually set with your hosting provider. They are not part of your domain’s zone file.

An SOA record or Start of Authority record labels a zone file with the name of the host where it was originally created.

Minimum TTL: The minimum amount of time other servers should keep data cached from this zone file.

An SPF record or Sender Policy Framework record lists the designated mail servers for a domain or subdomain.

An SPF record for your domain tells other receiving mail servers which outgoing server(s) are valid sources of email so they can reject spoofed mail from your domain that has originated from unauthorized servers.