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| − | =Annotations=
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| − | {{EclipseLink_API
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| − | |api=*org.eclipselink.annotations
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| − | *org.eclipselink.annotations
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| − | }}
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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. Annotations for object relational mapping are in the <tt>javax.persistence</tt> package.
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| − | {{EclipseLink_Spec
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| − | |link=http://jcp.org/en/jsr/detail?id=220
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| − | |section=Chapter 8 "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.
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| − | {{EclipseLink_Spec
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| − | |link=http://jcp.org/en/jsr/detail?id=220
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| − | |section=Section 10.1 "XML Overriding Rules"
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| − | }}
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| − | | + | '''[[Image:Elug_draft_icon.png|Warning]] See "Adding Metadata Using Annotations" in the [http://www.eclipse.org/eclipselink/documentation/ EclipseLink Concepts Guide]''' |
| − | ==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 <tt>org.eclipselink.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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| − | {{EclipseLink_JPA
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| − | |previous=[[EclipseLink/UserGuide/JPA/Basic JPA Development/Configuration/JPA/persistence.xml|persistence.xml]]
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| − | |next=[[EclipseLink/UserGuide/JPA/Basic JPA Development/Configuration/JPA/orm.xml|orm.xml]]
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| − | |up=[[EclipseLink/UserGuide/JPA/Basic JPA Development/Configuration|Configuration]]}}
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See "Adding Metadata Using Annotations" in the EclipseLink Concepts Guide