A proper way for JPA entities instantiation « Paul Szulc's Blog - 0 views
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A proper way for JPA entities instantiation
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creating the entities I would like to focus in this post
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JPA2.0 entities
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UserService
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UserDao
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FacebookWS
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User u
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UserService uses UserDAO and FacebookWS
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but don’t know how those dependencies are instantiated
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And you shouldn’t really care, all that is important is that UserService depends on dao and webservice object.
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BDD template given-when-then) tests are easy to read
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@Entity
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public class User
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calling new User(“someName”,”somePassowrd”, “someOtherName”, “someOtherPassword”) becomes hardly readable and maintainable
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code duplication
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Maintaining this code would turn into a nightmare in no time
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running the code above will throw an exception by the JPA provider,
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since not-nullable password field was never set.
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Joshua Blooch gives fine example of builder pattern.
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Instead of making the desired object directly, the client calls a constructor (or static factory) with all of the required parameters and gets a builder object. Then the client calls setter-like methods on the builder object to set each optional parameter of interest. Finally, the client calls a parameterless build method to generate the object, which is immutable. The builder is a static member class of the class it builds.
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Coffee
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public static class Builder
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Builder(CoffeeType type, int cupSize)
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Builder withMilk()
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Coffee build()
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Coffee(this)
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private Coffee(Builder builder)
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Coffee coffee = new Coffee.Builder(CoffeeType.Expresso, 3).withMilk().build();2}
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especially if most of those parameters are optional.
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For all entity attributes I create private fields
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those that are obligatory become parameters for the public constructor
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parameter-less constructor, I create one, but I give him
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protected access level
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protected
