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Difference between revisions of "EclipseLink/UserGuide/JPA/Basic JPA Development/Mapping/Basic Mappings"

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You may explicitly place an optional <tt>@Basic</tt> annotation on a field or property to explicitly mark it as persistent.
 
You may explicitly place an optional <tt>@Basic</tt> annotation on a field or property to explicitly mark it as persistent.
 
 
{{EclipseLink_Note
 
{{EclipseLink_Note
 
|note=The <tt>@Basic</tt> annotation is mostly for documentation purposes – it is not required for the field or property to be persistent.
 
|note=The <tt>@Basic</tt> annotation is mostly for documentation purposes – it is not required for the field or property to be persistent.
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* configure the fetch type to <tt>LAZY</tt><nowiki>;</nowiki>
 
* configure the fetch type to <tt>LAZY</tt><nowiki>;</nowiki>
 
* configure the mapping to forbid null values (for nonprimitive types) in case null values are inappropriate for your application.
 
* configure the mapping to forbid null values (for nonprimitive types) in case null values are inappropriate for your application.
 
+
{{EclipseLink_AttributeTable|caption=@Basic Attributes|content=<tr>
The <tt>@Basic</tt> annotation has the following attributes:
+
<td>'''<tt>fetch</tt>'''</td>
* <tt>fetch</tt> By default, EclipseLink persistence provider uses a fetch type of <tt>javax.persitence.FetchType.EAGER</tt><nowiki>: data must be eagerly fetched.</nowiki>If the default is inappropriate for your application or a particular persistent field, set <tt>fetch</tt> to <tt>FetchType.LAZY</tt><nowiki>: this is a hint to the persistence provider that data should be fetched lazily when it is first accessed (if possible).</nowiki>You are not required to specify the value of this attribute.<br>For more information, see [[Using%20EclipseLink%20JPA%20Extensions%20(ELUG)#What You May Need to Know About EclipseLink JPA Lazy Loading|What You May Need to Know About EclipseLink JPA Lazy Loading]].
+
<td> By default, EclipseLink persistence provider uses a fetch type of <tt>javax.persitence.FetchType.EAGER</tt><nowiki>: data must be eagerly fetched. If necessary, you can set <tt>fetch</tt> to <tt>FetchType.LAZY</tt>: this is a hint to the persistence provider that data should be fetched lazily when it is first accessed (if possible).
* <tt>optional</tt> By default, EclipseLink persistence provider assumes that the value of all (nonprimitive) fields and properties may be <tt>null</tt>.<br>If the default is inappropriate for your application, set this the value of this attribute to <tt>false</tt>.<br><br>You are not required to specify the value of this attribute.
+
{{EclipseLink_Note
 +
|note=For more information, see [[Using%20EclipseLink%20JPA%20Extensions%20(ELUG)#What You May Need to Know About EclipseLink JPA Lazy Loading|What You May Need to Know About EclipseLink JPA Lazy Loading]].}}
 +
</td>
 +
<td>Eager</td>
 +
<td>No></td>
 +
</tr>
 +
<tr>
 +
<td>'''<tt>optional</tt>'''</td>
 +
<td>By default, EclipseLink persistence provider assumes that the value of all (nonprimitive) fields and properties are optional and may be <tt>null</tt>.</td>
 +
<td>True</td>
 +
<td>No</td>
 +
</tr>
 +
}}
  
 
This example shows how to use this annotation to specify a fetch type of <tt>LAZY</tt> for a basic mapping.
 
This example shows how to use this annotation to specify a fetch type of <tt>LAZY</tt> for a basic mapping.

Revision as of 14:02, 17 June 2010

Basic Mappings

Simple Java types are mapped as part of the immediate state of an entity in its fields or properties. Mappings of simple Java types are called basic mappings.

For all mapping types there are a common set of options:

  • Read-Only: Specifies that the mapping should populate the value on read and copy. Required when multiple mappings share the same database column.
    See Configuring Read-Only Mappings in the EclipseLink User's Guide for details.
  • Converters allow custom data types and data conversions to be used with most mapping types
    • Annotations: @Converter, @TypeConverter, @ObjectTypeConverter, @StructConverter, @Convert
    • XML: <converter>, <type-converter>, <object-type-converter>, <struct-converter>, <convert>
    See Converters and Transformers in the EclipseLink User's Guide for details.

By default, EclipseLink persistence provider automatically configures a basic mapping for simple types.

Use the following annotations to fine-tune how your database implements these mappings:

  • @Basic
  • @Enumerated
  • @Temporal
  • @Lob
  • @Transient

For additional mapping information, see Default Conversions and Converters


@Basic

By default, EclipseLink persistence provider automatically configures @Basic mapping for most Java primitive types, wrappers of the primitive types, and enumerated types.

EclipseLink uses the default column name format of <field-name> or <property-name> in uppercase characters.

You may explicitly place an optional @Basic annotation on a field or property to explicitly mark it as persistent.

Elug note icon.png

Note: The @Basic annotation is mostly for documentation purposes – it is not required for the field or property to be persistent.


Use the @Basic annotation to do the following:

  • configure the fetch type to LAZY;
  • configure the mapping to forbid null values (for nonprimitive types) in case null values are inappropriate for your application.

{{EclipseLink_AttributeTable|caption=@Basic Attributes|content=<tr>

<td>fetch</td>
<td> By default, EclipseLink persistence provider uses a fetch type of javax.persitence.FetchType.EAGER: data must be eagerly fetched. If necessary, you can set <tt>fetch</tt> to <tt>FetchType.LAZY</tt>: this is a hint to the persistence provider that data should be fetched lazily when it is first accessed (if possible).
{{EclipseLink_Note
|note=For more information, see [[Using%20EclipseLink%20JPA%20Extensions%20(ELUG)#What You May Need to Know About EclipseLink JPA Lazy Loading|What You May Need to Know About EclipseLink JPA Lazy Loading]].}}
</td>
 <td>Eager</td>
 <td>No></td>
</tr>
<tr>
 <td>'''<tt>optional</tt>'''</td>
 <td>By default, EclipseLink persistence provider assumes that the value of all (nonprimitive) fields and properties are optional and may be <tt>null</tt>.</td>
 <td>True</td>
 <td>No</td>
</tr>
}}

This example shows how to use this annotation to specify a fetch type of <tt>LAZY</tt> for a basic mapping.


<span id="Example 18-11"></span>
''''' Usage of the @Basic Annotation'''''
<source lang="java">
 @Entity
 public class Employee implements Serializable {
     ...
     @Basic(fetch=LAZY)
     protected String getName() {
         return name;
     }
     ...
 }
</source>

For more information and examples, see Section 9.1.18 "Basic Annotation" of the [http://jcp.org/en/jsr/detail?id=220 JPA Specification].

For more information on EclipseLink direct mappings and relationship mappings, see [[Introduction%20to%20Relational%20Mappings%20(ELUG)#Relational Mapping Types|Relational Mapping Types]].


{{EclipseLink_JPA
|previous=[[EclipseLink/UserGuide/JPA/Basic JPA Development/Mapping/Entity/Id|Id]]
|next=[[EclipseLink/UserGuide/JPA/Basic JPA Development/Mapping/Basic Mappings/Column|Column]]
|up=[[EclipseLink/UserGuide/JPA/Basic JPA Development/Mapping|Mapping]]}}