View source for Configuring a Relational Many-to-Many Mapping (ELUG)

<div style="float:right;border:1px solid #000000;padding:5px">__TOC__
[[Special:Whatlinkshere/Configuring a Relational Many-to-Many Mapping (ELUG)|Related Topics]]</div>

For information on how to create EclipseLink mappings, see [[Creating%20a%20Mapping%20(ELUG)|Creating a Mapping]].

This table lists the configurable options for a relational many-to-many mapping.

<span id="Table 39-1">

{| class="RuleFormalMax" dir="ltr" title="Configurable Options for Relational Many-to-Many Mapping" summary="This table lists the configurable options common to Relational Many-to-Many Mapping and categorizes them as Basic and Advanced and indicates if the option can be configured with the Workbench, Java, or both." width="100%" border="1" frame="border" rules="all" cellpadding="3" frame="border" rules="all"
|- align="left" valign="top"
! id="r1c1-t2" align="left" valign="bottom" | '''Option to Configure'''
! id="r1c2-t2" align="left" valign="bottom" | '''Workbench'''
! id="r1c3-t2" align="left" valign="bottom" | '''Java'''
|- align="left" valign="top"
| id="r2c1-t2" headers="r1c1-t2" align="left" |
[[Configuring%20a%20Relational%20Mapping%20(ELUG)#Configuring Reference Descriptor|Configuring Reference Descriptor]]
| headers="r2c1-t2 r1c2-t2" align="left" |
[[Image:support.gif|Supported]]
| headers="r2c1-t2 r1c3-t2" align="left" |
[[Image:support.gif|Supported]]
|- align="left" valign="top"
| id="r3c1-t2" headers="r1c1-t2" align="left" |
[[Configuring%20a%20Mapping%20(ELUG)#Configuring Method or Direct Field Accessing at the Mapping Level|Method or direct field access ]]
| headers="r3c1-t2 r1c2-t2" align="left" |
[[Image:support.gif|Supported]]
| headers="r3c1-t2 r1c3-t2" align="left" |
[[Image:support.gif|Supported]]
|- align="left" valign="top"
| id="r4c1-t2" headers="r1c1-t2" align="left" |
[[Configuring%20a%20Mapping%20(ELUG)#Configuring Read-Only Mappings|Read-only mapping]]
| headers="r4c1-t2 r1c2-t2" align="left" |
[[Image:support.gif|Supported]]
| headers="r4c1-t2 r1c3-t2" align="left" |
[[Image:support.gif|Supported]]
|- align="left" valign="top"
| id="r5c1-t2" headers="r1c1-t2" align="left" |
[[Configuring%20a%20Mapping%20(ELUG)#Configuring Private or Independent relationships|Private or Independent relationships]]
| headers="r5c1-t2 r1c2-t2" align="left" |
[[Image:support.gif|Supported]]
| headers="r5c1-t2 r1c3-t2" align="left" |
[[Image:support.gif|Supported]]
|- align="left" valign="top"
| id="r6c1-t2" headers="r1c1-t2" align="left" |
[[Configuring%20a%20Relational%20Mapping%20(ELUG)#Configuring Batch Reading|Batch reading]]
| headers="r6c1-t2 r1c2-t2" align="left" |
[[Image:support.gif|Supported]]
| headers="r6c1-t2 r1c3-t2" align="left" |
[[Image:support.gif|Supported]]
|- align="left" valign="top"
| id="r7c1-t2" headers="r1c1-t2" align="left" |
[[Configuring%20a%20Mapping%20(ELUG)#Configuring Indirection (lazy loading)|Indirection (lazy loading)]]
| headers="r7c1-t2 r1c2-t2" align="left" |
[[Image:support.gif|Supported]]
| headers="r7c1-t2 r1c3-t2" align="left" |
[[Image:support.gif|Supported]]
|- align="left" valign="top"
| id="r8c1-t2" headers="r1c1-t2" align="left" |
[[Configuring%20a%20Mapping%20(ELUG)#Configuring Bidirectional Relationship|Bidirectional relationship ]]
| headers="r8c1-t2 r1c2-t2" align="left" |
[[Image:support.gif|Supported]]
| headers="r8c1-t2 r1c3-t2" align="left" |
[[Image:support.gif|Supported]]
|- align="left" valign="top"
| id="r9c1-t2" headers="r1c1-t2" align="left" |
[[Configuring%20a%20Mapping%20(ELUG)#Configuring Mapping Comments|Container policy]]
| headers="r9c1-t2 r1c2-t2" align="left" |
[[Image:support.gif|Supported]]
| headers="r9c1-t2 r1c3-t2" align="left" |
[[Image:support.gif|Supported]]
|- align="left" valign="top"
| id="r10c1-t2" headers="r1c1-t2" align="left" |
[[Configuring%20a%20Mapping%20(ELUG)#Configuring Mapping Comments|Mapping comments]]
| headers="r10c1-t2 r1c2-t2" align="left" |
[[Image:support.gif|Supported]]
| headers="r10c1-t2 r1c3-t2" align="left" |
[[Image:unsupport.gif|Supported]]
|- align="left" valign="top"
| id="r11c1-t2" headers="r1c1-t2" align="left" |
[[#Configuring a Relation Table|Relational table ]]
| headers="r11c1-t2 r1c2-t2" align="left" |
[[Image:support.gif|Supported]]
| headers="r11c1-t2 r1c3-t2" align="left" |
[[Image:support.gif|Supported]]
|- align="left" valign="top"
| id="r12c1-t2" headers="r1c1-t2" align="left" |
[[Configuring%20a%20Relational%20Mapping%20(ELUG)#Configuring Table and Field References (Foreign and Target Foreign Keys)|Table and field references ]] (Source)
| headers="r12c1-t2 r1c2-t2" align="left" |
[[Image:support.gif|Supported]]
| headers="r12c1-t2 r1c3-t2" align="left" |
[[Image:support.gif|Supported]]
|- align="left" valign="top"
| id="r13c1-t2" headers="r1c1-t2" align="left" |
[[Configuring%20a%20Relational%20Mapping%20(ELUG)#Configuring Table and Field References (Foreign and Target Foreign Keys)|Table and field references ]] (Target)
| headers="r13c1-t2 r1c2-t2" align="left" |
[[Image:support.gif|Supported]]
| headers="r13c1-t2 r1c3-t2" align="left" |
[[Image:support.gif|Supported]]
|- align="left" valign="top"
| id="r14c1-t2" headers="r1c1-t2" align="left" |
[[Configuring%20a%20Relational%20Mapping%20(ELUG)#Configuring Query Key Order|Query key order ]]
| headers="r14c1-t2 r1c2-t2" align="left" |
[[Image:support.gif|Supported]]
| headers="r14c1-t2 r1c3-t2" align="left" |
[[Image:support.gif|Supported]]
|}


This example shows how to create a many-to-many mapping and add it to a descriptor using Java code.

<span id="Example 41-1"></span>
''''' Many-to-Many Mapping'''''

<pre>
public void customize(ClassDescriptor descriptor) { 
    ManyToManyMapping mapping = new ManyToManyMapping();  

    // configure mapping
    ... 

    // add mapping to descriptor
    descriptor.addMapping(mapping);
}
</pre>

For more information, see the following:
* [[Introduction%20to%20Relational%20Mappings%20(ELUG)#Many-to-Many Mapping|Many-to-Many Mapping]]
* [[Configuring%20a%20Relational%20Mapping%20(ELUG)|Configuring a Relational Mapping]]
* [[Configuring%20a%20Mapping%20(ELUG)|Configuring a Mapping]].


For information on using JPA to configure many-to-many mappings, see [[Introduction%20to%20EclipseLink%20JPA%20(ELUG)#@ManyToMany|@ManyToMany]].



==Configuring a Relation Table==

The relation table contains the columns for the primary keys of the source table and target table involved in the many-to-many mapping. You must create this table in the database before completing the mapping. See [[Using%20Workbench%20(ELUG)#Using Databases|Using Databases]] for information on creating database tables.

In the [[Introduction%20to%20Relational%20Mappings%20(ELUG)#Figure 32-5|Many-to-Many Relationships ]] figure, the <tt>PROJ_EMP</tt> table serves as the relation table between the <tt>PROJECT</tt> and <tt>EMPLOYEE</tt> tables.


===How to Configure a Relation Table Using Workbench===

To select a relation table for a mapping, use this procedure:
# Select the mapped attribute in the '''Navigator'''. Its properties appear in the Editor.
# Click the '''General''' tab. The General tab appears.<br><span id="Figure 39-1"></span>''''' Table Reference Tab, Relation Table Option'''''<br>[[Image:mmreltabl.gif|Table Reference Tab, Relation Table Option]]
#Use the '''Relation Table''' field to select a database table to define this mapping.


===How to Configure a Relation Table Using Java===

Many-to-many mappings represent the relationships between a collection of source objects and a collection of target objects. This requires an intermediate table that manages the associations between the source and target records.

Many-to-many mappings are instances of the <tt>ManyToManyMapping</tt> class and requires the following elements:
* The attribute mapped, set by using the <tt>setAttributeName</tt> method.
* The reference class, set by using the <tt>setReferenceClass</tt> method.
* The relation table, set by using the <tt>setRelationTableName</tt><tt>()</tt> method.
* The foreign key information (for noncomposite target primary keys), which you specify by calling the <tt>setSourceRelationKeyFieldName</tt> and <tt>setTargetRelationKeyFieldName</tt> methods.
* The foreign key information if the source or target primary keys are composite, which you specify by sending the <tt>addSourceRelationKeyFieldName</tt> or <tt>addTargetRelationKeyFieldName</tt> methods.


<span id="Example 39-1"></span>
''''' Configuring a Relational Table'''''
 public void customize(ClassDescriptor descriptor) { 
 '''    // In the Employee class, create the mapping that references Project class'''
     ManyToManyMapping manyToManyMapping = new ManyToManyMapping();
     manyToManyMapping.setAttributeName("projects");
     manyToManyMapping.setReferenceClass(Project.class);
 
     '''// Configure the relational table'''
     manyToManyMapping.setRelationTableName("PROJ_EMP");
     manyToManyMapping.setSourceRelationKeyFieldName ("EMPID");
     manyToManyMapping.setTargetRelationKeyFieldName ("PROJID");
 
     '''// Add mapping to descriptor'''
 
     descriptor.addMapping(manyToManyMapping);
 }

In addition to the API that [[#Example 39-1|Configuring a Relational Table]] illustrates, other common API for use with many-to-many mappings include the following:
* <tt>useBasicIndirection</tt><nowiki>: implements EclipseLink value holder indirection.</nowiki>
* <tt>useTransparentCollection</tt><nowiki>: if you use transparent indirection, this element places a special collection in the source object's attribute.</nowiki>
* <tt>dontUseIndirection</tt><nowiki>: implements no indirection.</nowiki>

For more information about the available methods for <tt>ManyToManyMapping</tt>, see the ''EclipseLink API Reference''.




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