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| − | {{EclipseLink_UserGuide
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| − | |info=y
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| − | |toc=n
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| − | |eclipselink=y
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| − | |eclipselinktype=JPA
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| − | |api=y
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| − | |apis=
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| − | * [http://www.eclipse.org/eclipselink/api/latest/javax/persistence/Entity.html @Entity]
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| − | * [http://www.eclipse.org/eclipselink/api/latest/javax/persistence/package-summary.html javax.persistence]
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| − | * [http://www.eclipse.org/eclipselink/api/latest/org/eclipse/persistence/annotations/package-summary.html org.eclipse.persistence.annotations]
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| − | |examples=y
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| − | |example=
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| − | * [http://wiki.eclipse.org/EclipseLink/Examples/JPA/2.0/Employee Employee JPA 2]
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| − | |1=*javax.persistence
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| − | |2=*org.eclipselink.annotations
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| − | }}
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| | | | |
| − | = Adding Metadata Using Annotations =
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| − | An annotation is a simple, expressive means of decorating Java source code with metadata that is compiled into the corresponding Java class files for interpretation at run time by a JPA persistence provider to manage persistent behavior.
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| − | A metadata annotation represents a Java language feature that lets you attach structured and typed metadata to the source code. Annotations alone are sufficient for the metadata specification -- you do not need to use XML. Standard JPA annotations are in the [http://www.eclipse.org/eclipselink/api/latest/javax/persistence/package-summary.html <tt>javax.persistence</tt>] package. {{EclipseLink_Spec
| + | '''[[Image:Elug_draft_icon.png|Warning]] See "Adding Metadata Using Annotations" in the [http://www.eclipse.org/eclipselink/documentation/ EclipseLink Concepts Guide]''' |
| − | |link=http://jcp.org/en/jsr/detail?id=220 | + | |
| − | |section=Chapter 10 "Metadata Annotations"
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| − | }}
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| − | An object relational mapping XML file is optional. If you choose to provide one, then it should contain mapping information for the classes listed in it. The persistence provider loads an [[EclipseLink/UserGuide/JPA/Basic JPA Development/Configuration/JPA/orm.xml|orm.xml file]] (or other mapping file) as a resource. If you provide a mapping file, the classes and mapping information specified in the mapping file will be used. The XML mapping metadata may combine with and override annotation metadata. {{EclipseLink_Spec
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| − | |link=http://jcp.org/en/jsr/detail?id=220
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| − | |section=Section 12.2 "XML Overriding Rules"
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| − | }}
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| − | | + | |
| − | Standard JPA 2.0 annotations are in the [http://www.eclipse.org/eclipselink/api/latest/javax/persistence/package-summary.html javax.persistence] package.
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| − | EclipseLink-specific JPA annotations are in the [http://www.eclipse.org/eclipselink/api/2.2/org/eclipse/persistence/annotations/package-summary.html org.eclipse.persistence.annotations package].
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| − | <br>
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| − | | + | |
| − | == Using Metadata Annotations ==
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| − | Use annotations to configure the persistent behavior of your entities. For example, to designate a Java class as a JPA entity, use the <tt>@Entity</tt> annotation as shown in this example:
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| − | | + | |
| − | <source lang="java">
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| − | @Entity
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| − | public class Employee implements Serializable {
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| − | ...
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| − | }
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| − | </source>
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| − | | + | |
| − | You can apply annotations at the following levels:
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| − | | + | |
| − | *Class
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| − | *Method
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| − | *Field
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| − | EclipseLink defines a set of proprietary annotations to take advantage of EclipseLink-specific features. You can find them in the [http://www.eclipse.org/eclipselink/api/latest/org/eclipse/persistence/annotations/package-summary.html <tt>org.eclipse..persistence.annotations</tt>] package. These annotations are not available through the use of JPA metadata.
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| − | | + | |
| − | == Advantages and Disadvantages of Using Annotations ==
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| − | Using annotations provides several advantages:
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| − | *They are relatively simple to use and understand.
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| − | *They provide in-line metadata within with the code that it describes; you do not need to replicate the source code context of where the metadata applies.
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| − | The primary disadvantage of annotations is that the metatdata becomes unnecessarily coupled to the code; changes to metadata require changing the source code.
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| − | <br>
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| − | <br> {{EclipseLink_JPA
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| − | |previous=[[EclipseLink/UserGuide/JPA/Basic JPA Development/Configuration/JPA/persistence.xml|Configuring Persistence Units Using persistence.xml ]]
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| − | |next=[[EclipseLink/UserGuide/JPA/Basic JPA Development/Configuration/JPA/orm.xml|Specifying Object-Relational Mappings Using orm.xml]]
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| − | |up=[[EclipseLink/UserGuide/JPA/Basic JPA Development/Configuration|Configuration]]
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| − | |version=2.2.0 DRAFT}}
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See "Adding Metadata Using Annotations" in the EclipseLink Concepts Guide