Difference between revisions of "Configuring an Object-Relational Data Type Mapping (ELUG)"

Revision as of 12:51, 30 November 2007

This section describes how to configure an object-relational data type mapping.

For information on how to configure EclipseLink mappings options common to two or more mapping types, see Configuring a Mapping.

For information on how to create EclipseLink mappings, see Creating a Mapping (ELUG)#Creating a Mapping.

Introduction to Object-Relational Data Type Mapping Configuration

This table lists the types of object-relational data type mappings that you can configure and provides a cross-reference to the type-specific chapter that lists the configurable options supported by that type.

Configuring Object-Relational Data Type Mappings

For more information, see the following:

• [Introduction%20to%20Mappings%20(ELUG)#Chapter 16, "Introduction to Mappings"]
• [Introduction%20to%20Relational%20Mappings%20(ELUG)#Chapter 32, "Introduction to Relational Mappings"]

Configuring Common Object-Relational Data Type Mapping Options

[[#Table 50-2] lists the configurable options shared by two or more object-relational data type mapping types. In addition to the configurable options described here, you must also configure the options described for the specific object-relational data type mapping types (see [Introduction%20to%20Object-Relational%20Data%20Type%20Mappings%20(ELUG)#Object-Relational Data Type Mapping Types]), as shown in [[#Table 50-1].

Table 50-2 Common Options for Object-Relational Data Type Mappings

Configuring Reference Class

When mapping an attribute that involves a relationship to another class, you must specify the reference class–the Java class to which the mapped attribute refers.

[[#Table 50-3] summarizes which object-relational data type mappings support this option.

Table 50-3 Mapping Support for Reference Class

How to Configure Reference Class Using Java

Use org.eclipse.persistence.mappings.ForeignReferenceMapping method setReferenceClass to specify the target class of the attribute being mapped.

[[#Example 50-1] shows how to use this method with a ReferenceMapping that maps the manager attribute of the Employee class.

Example 50-1 Configuring Reference Class in Java

public void customize(ClassDescriptor descriptor) { 
    ReferenceMapping managerMapping = new ReferenceMapping();
    managerMapping.setReferenceClass("Employee.class"); // set reference class
    managerMapping.setAttributeName("manager");

    // add this mapping to descriptor
    descriptor.addMapping (managerMapping);
}

For more information, see the EclipseLink API Reference.

Configuring Attribute Name

All object-relational data type mappings map an attribute in a Java object to field in the database. The attribute name is the name of the attribute being mapped. The name is as specified in the reference class (see [[#Configuring Reference Class]).

[[#Table 50-4] summarizes which object-relational data type mappings support this option.

Table 50-4 Mapping Support for Attribute Name

How to Configure Attribute Name Using Java

Use org.eclipse.persistence.mappings.DatabaseMapping method setAttributeName to specify the name of the attribute being mapped.

[[#Example 50-2] shows how to use this method with a ReferenceMapping that maps the manager attribute of the Employee class.

Example 50-2 Configuring Attribute Name in Java

public void customize(ClassDescriptor descriptor) { 
    ReferenceMapping managerMapping = new new ReferenceMapping();
    managerMapping.setReferenceClass("Employee.class"); 
    managerMapping.setAttributeName("manager"); // set attribute name

    // add this mapping to descriptor
    descriptor.addMapping (managerMapping);
}

For more information, see the EclipseLink API Reference.

Configuring Field Name

All object-relational data type mappings require the name of database field to which their specified attribute is mapped. This field name can be the column name of a database table or the name of a field in an object type created on the database.

[[#Table 50-5] summarizes which object-relational data type mappings support this option.

Table 50-5 Mapping Support for Field Name

How to Configure Field Name Using Java

Use the object-relational data type mapping method setFieldName to specify the database field to which the attribute is mapped.

[[#Example 50-3] shows how to use this method with an ObjectArrayMapping that maps the Employee class attribute phone to database field name PHONE_NUMBER.

Example 50-3 Configuring Field Name in Java

public void customize(ClassDescriptor descriptor) { 
    ObjectArrayMapping phonesMapping = new ObjectArrayMapping();
    phonesMapping.setReferenceClass("Employee.class");
    phonesMapping.setAttributeName("phone");
    phonesMapping.setFieldName("PHONE_NUMBER"); // set field name

    // add this mapping to descriptor
    descriptor.addMapping (phonesMapping);
}

For more information, see the EclipseLink API Reference.

Configuring Structure Name

Certain object-relational data type mappings require the specification of the data type or structure name of the field being mapped. The structure name is the name of the array or table type that defines the field.

[[#Table 50-6] summarizes which object-relational data type mappings support this option.

Table 50-6 Mapping Support for Structure Name

How to Configure Structure Name Using Java

Use the object-relational data type mapping method setStructureName to specify the structure of the attribute being mapped.

This example shows how to use this method with an ObjectArrayMapping that maps the Employee class attribute phones to database field name PHONE_NUMBERS of type PHONE_ARRAY_TYPE.

Configuring Structure Name in Java

public void customize(ClassDescriptor descriptor) { 
    ObjectArrayMapping phonesMapping = new ObjectArrayMapping();
    phonesMapping.setReferenceClass("Employee.class");
    phonesMapping.setAttributeName("phones");
    phonesMapping.setFieldName("PHONE_NUMBERS");
    phonesMapping.setStructureName("PHONE_ARRAY_TYPE"); // set structure name

    // add this mapping to descriptor
    descriptor.addMapping (phonesMapping);
}

For more information, see the EclipseLink API Reference.

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