Configuring a Relational Variable One-to-One Mapping (ELUG)

Related Topics

For information on how to create EclipseLink mappings, see Creating a Mapping.

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

Option	Workbench	Java
Configuring Reference Descriptor
Configuring a Type Conversion Converter
Configuring Read-Only Mappings
Configuring Mapping Comments
Configuring Mapping Comments
Configuring Mapping Comments
Configuring Query Key Association
Configuring Class Indicator
Configuring Unique Primary Key

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

Variable One-to-One Mapping

public void customize(ClassDescriptor descriptor) { 
   VariableOneToOneMapping mapping = new VariableOneToOneMapping();  

   // configure mapping
   ... 

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

For more information, see the following:

• Variable One-to-One Mapping
• Configuring a Relational Mapping
• Configuring a Mapping.

Configuring Class Indicator

In variable one-to-one mappings, you can use an indicator column in the source table to specify the correct target table, as illustrated in Variable One-to-One Mapping using Class indicator Field. This section includes information on implementing class indicators.

A source table has an indicator column that specifies the target table through the class indicator field.

The Variable One-to-One Mapping using Class indicator Field figure illustrates the EMPLOYEE table that has a TYPE column that indicates the target for the row (either PHONE or EMAIL).

Variable One-to-One Mapping using Class indicator Field

The principles of defining such a variable class relationship are similar to defining a normal one-to-one relationship, except:

• The reference class is a Java interface, not a Java class. However, the method to set the interface is identical.
• You must specify a type indicator field.
• You specify the class indicator values on the mapping so that mapping can determine the class of object to create.
• You must specify the foreign key names and the respective abstract query keys from the target interface descriptor.

Alternatively, you can use unique primary keys to specify the correct target. See Configuring Unique Primary Key for more information.

How to Configure a Class Indicator Using Workbench

To specify the class indicators for a variable one-to-one mapping, use this procedure:

1. Select the variable one-to-one mapping in the Navigator. Its attributes appear in the Editor.
2. Click the Class Indicator Info tab. The Class Indicator Info tab appears.
   Figure 37-2 Class Indicator Info Tab'
   
3. Use the Class Indicator Field to select the field on the database table (associated with the mapping's descriptor) to use as the indicator for the variable mapping.
4. Use the Indicator Type to specify the data type of the class indicator field by selecting the data type from the list.
5. To specify the specific class indicator field values for each (nonabstract) child class, click Edit and enter the appropriate value for each child class.

How to Configure a Class Indicator Using Java

This example illustrates how to define a variable one-to-one mapping using a class (type) indicator in Java code.

Defining Variable One-to-One Mapping Using a Class Indicator

public void customize(ClassDescriptor descriptor) { 
    VariableOneToOneMapping variableOneToOneMapping = new VariableOneToOneMapping();  
    variableOneToOneMapping.setAttributeName("contact");  
    variableOneToOneMapping.setReferenceClass (Contact.class);  
    variableOneToOneMapping.setForeignQueryKeyName ("C_ID", "id");  
    variableOneToOneMapping.setTypeFieldName("TYPE");  

    // configure class indicators
    variableOneToOneMapping.addClassIndicator(Email.class, "Email");   
    variableOneToOneMapping.addClassIndicator(Phone.class, "Phone");  

    variableOneToOneMapping.dontUseIndirection();  
    variableOneToOneMapping.privateOwnedRelationship();  

    // add mapping to descriptor
    descriptor.addMapping(variableOneToOneMapping);
}

For more information about the available methods for VariableOneToOneMapping, see the EclipseLink API Reference.

Configuring Unique Primary Key

In variable one-to-one mappings, you can use a unique primary key in the source table to specify the correct target table, as illustrated in the Variable One-to-One Relationship with Unique Primary Key figure. This section includes information on implementing class indicators.

Alternatively, you can use a class indicator to specify the correct target. See Configuring Class Indicator for more information.

How to Configure a Unique Primary Key UsingWorkbench

To specify the variable one-to-one mapping with a primary key, use this procedure:

1. Select the variable one-to-one mapping in the Navigator. Its attributes appear in the Editor.
2. Click the Class Indicator Info tab. The Class Indicator Info tab appears.
   Figure 37-3 Class Indicator Info Tab, Configuring Primary Key
   
   • Use the Class Indicator Field to select none.
   • Use the Indicator Type to select none.
   • Use the Indicator Value column to specify none.
3. After choosing the reference descriptor for the mapping, deselect the Include check boxes.

Note: You cannot deselect the value in the Class Indicator Field, unless the foreign key values in the source table are unique.

How to Configure a Unique Primary Key Using Java

This example illustrates how to define a variable one-to-one mapping using a unique primary key in Java code.

Defining Variable One-to-One Mapping Using a Unique Primary Key

public void customize(ClassDescriptor descriptor) { 
    VariableOneToOneMapping variableOneToOneMapping = new VariableOneToOneMapping();  
    variableOneToOneMapping.setAttributeName("contact");  
    variableOneToOneMapping.setReferenceClass (Contact.class);  
    variableOneToOneMapping.setForeignQueryKeyName ("C_ID", "id");  
    variableOneToOneMapping.dontUseIndirection();  
    variableOneToOneMapping.privateOwnedRelationship();

    // add mapping to descriptor
    descriptor.addMapping(variableOneToOneMapping);
}

For more information about the available methods for VariableOneToOneMapping, see the EclipseLink API Reference.

What You May Need to Know About Unique Primary Keys

As the Variable One-to-One Relationship with Unique Primary Key figure illustrates, the value of the foreign key in the source table (C_ID) mapped to the primary key of the target table is unique. No primary key values among the target tables are the same, so primary key values are not unique just in the table, but also among the tables.

Variable One-to-One Relationship with Unique Primary Key

If there is no indicator stored in the source table, EclipseLink cannot determine to which target table the foreign key value is mapped. Therefore, EclipseLink reads through all the target tables until it finds an entry in one of the target tables. This is an inefficient way of setting up a relation model. The class indicator is much more efficient as it reduces the number of reads performed on the tables to get the data. In the class indicator method, EclipseLink knows exactly which target table to look into for the data.

The principles of defining such a variable class relationship are similar to defining class indicator variable one-to-one relationships, except the following:

• A type indicator field is not specified.
• The class indicator values are not specified.

The type indicator field and its values are not needed, because EclipseLink goes through all the target tables until data is finally found.

Configuring Query Key Association

This section includes information on configuring query key assosications using development tools, as well as Java.

How to Configure a Query Key Association Using Workbench

To specify the query keys used for a variable one-to-one mapping, use this procedure:

1. Select the variable one-to-one mapping in the Navigator. Its attributes appear in the Editor.
2. Click the Query Key Associations tab. The Query Key Associations tab appears
   Query Key Associations Tab
   
3. Complete each field on the Query Key Associations tab.
4. Use the Indicator Type to specify the data type of the class indicator field by selecting the data type from the list.

Field	Description
Foreign Key	The field from the database table to use as the foreign key in this relationship.
Query Key Name	The name of the query key (from the referenced descriptor) for this association. See Configuring Query Keys for more information.

How to Configure a Query Key Association Using Java

The API to configure query key associations is org.eclipse.persistence.mappings.VariableOneToOneMapping method addForeingQueryKeyName(String, String).

For more information about the available methods for VariableOneToOneMapping, see the EclipseLink API Reference.

Configuring Class Indicator

In variable one-to-one mappings, you can use an indicator column in the source table to specify the correct target table, as illustrated in the Variable One-to-One Mapping using Class indicator Field figure. This section includes information on implementing class indicators.

A source table has an indicator column that specifies the target table through the class indicator field.

The Variable One-to-One Mapping using Class indicator Field figure illustrates the EMPLOYEE table that has a TYPE column that indicates the target for the row (either PHONE or EMAIL).

Variable One-to-One Mapping using Class indicator Field

The principles of defining such a variable class relationship are similar to defining a normal one-to-one relationship, except:

• The reference class is a Java interface, not a Java class. However, the method to set the interface is identical.
• You must specify a type indicator field.
• You specify the class indicator values on the mapping so that mapping can determine the class of object to create.
• You must specify the foreign key names and the respective abstract query keys from the target interface descriptor.

Alternatively, you can use unique primary keys to specify the correct target. See Configuring Unique Primary Key for more information.

How to Configure a Class Indicator Using Workbench

To specify the class indicators for a variable one-to-one mapping, use this procedure:

1. Select the variable one-to-one mapping in the Navigator. Its attributes appear in the Editor.
2. Click the Class Indicator Info tab. The Class Indicator Info tab appears.
   Class Indicator Info Tab'
   
3. Use the Class Indicator Field to select the field on the database table (associated with the mapping's descriptor) to use as the indicator for the variable mapping.
4. Use the Indicator Type to specify the data type of the class indicator field by selecting the data type from the list.
5. To specify the specific class indicator field values for each (nonabstract) child class, click Edit and enter the appropriate value for each child class.

How to Configure a Class Indicator Using Java

This example illustrates how to define a variable one-to-one mapping using a class (type) indicator in Java code.

Defining Variable One-to-One Mapping Using a Class Indicator

public void customize(ClassDescriptor descriptor) { 
    VariableOneToOneMapping variableOneToOneMapping = new VariableOneToOneMapping();  
    variableOneToOneMapping.setAttributeName("contact");  
    variableOneToOneMapping.setReferenceClass (Contact.class);  
    variableOneToOneMapping.setForeignQueryKeyName ("C_ID", "id");  
    variableOneToOneMapping.setTypeFieldName("TYPE");  

    // configure class indicators
    variableOneToOneMapping.addClassIndicator(Email.class, "Email");   
    variableOneToOneMapping.addClassIndicator(Phone.class, "Phone");  

    variableOneToOneMapping.dontUseIndirection();  
    variableOneToOneMapping.privateOwnedRelationship();  

    // add mapping to descriptor
    descriptor.addMapping(variableOneToOneMapping);
}

For more information about the available methods for VariableOneToOneMapping, see the EclipseLink API Reference.

Configuring Unique Primary Key

In variable one-to-one mappings, you can use a unique primary key in the source table to specify the correct target table, as illustrated in the Variable One-to-One Relationship with Unique Primary Key figure. This section includes information on implementing class indicators.

Alternatively, you can use a class indicator to specify the correct target. See Configuring Class Indicator for more information.

How to Configure a Unique Primary Key UsingWorkbench

To specify the variable one-to-one mapping with a primary key, use this procedure:

1. Select the variable one-to-one mapping in the Navigator. Its attributes appear in the Editor.
2. Click the Class Indicator Info tab. The Class Indicator Info tab appears.
   Class Indicator Info Tab, Configuring Primary Key
   
3. Use the Class Indicator Field to select none.
4. Use the Indicator Type to select none.
5. Use the Indicator Value column to specify none.
6. After choosing the reference descriptor for the mapping, deselect the Include check boxes.

Note: You cannot deselect the value in the Class Indicator Field, unless the foreign key values in the source table are unique.

How to Configure a Unique Primary Key Using Java

This example illustrates how to define a variable one-to-one mapping using a unique primary key in Java code.

Defining Variable One-to-One Mapping Using a Unique Primary Key

public void customize(ClassDescriptor descriptor) { 
    VariableOneToOneMapping variableOneToOneMapping = new VariableOneToOneMapping();  
    variableOneToOneMapping.setAttributeName("contact");  
    variableOneToOneMapping.setReferenceClass (Contact.class);  
    variableOneToOneMapping.setForeignQueryKeyName ("C_ID", "id");  
    variableOneToOneMapping.dontUseIndirection();  
    variableOneToOneMapping.privateOwnedRelationship();

    // add mapping to descriptor
    descriptor.addMapping(variableOneToOneMapping);
}

For more information about the available methods for VariableOneToOneMapping, see the EclipseLink API Reference.

What You May Need to Know About Unique Primary Keys

As the Variable One-to-One Relationship with Unique Primary Key figure illustrates, the value of the foreign key in the source table (C_ID) mapped to the primary key of the target table is unique. No primary key values among the target tables are the same, so primary key values are not unique just in the table, but also among the tables.

Variable One-to-One Relationship with Unique Primary Key

If there is no indicator stored in the source table, EclipseLink cannot determine to which target table the foreign key value is mapped. Therefore, EclipseLink reads through all the target tables until it finds an entry in one of the target tables. This is an inefficient way of setting up a relation model. The class indicator is much more efficient as it reduces the number of reads performed on the tables to get the data. In the class indicator method, EclipseLink knows exactly which target table to look into for the data.

The principles of defining such a variable class relationship are similar to defining class indicator variable one-to-one relationships, except the following:

• A type indicator field is not specified.
• The class indicator values are not specified.

The type indicator field and its values are not needed, because EclipseLink goes through all the target tables until data is finally found.

Configuring Query Key Association

This section includes information on configuring query key assosications using development tools, as well as Java.

How to Configure a Query Key Association Using Workbench

To specify the query keys used for a variable one-to-one mapping, use this procedure:

1. Select the variable one-to-one mapping in the Navigator. Its attributes appear in the Editor.
2. Click the Query Key Associations tab. The Query Key Associations tab appears.
   Query Key Associations Tab
   
3. Complete each field on the Query Key Associations tab.
4. Use the Indicator Type to specify the data type of the class indicator field by selecting the data type from the list.

Use the following information to enter data in each field on the tab:

Field	Description
Foreign Key	The field from the database table to use as the foreign key in this relationship.
Query Key Name	The name of the query key (from the referenced descriptor) for this association. See Configuring Query Keys for more information.

How to Configure a Query Key Association Using Java

The API to configure query key associations is org.eclipse.persistence.mappings.VariableOneToOneMapping method addForeingQueryKeyName(String, String).

For more information about the available methods for VariableOneToOneMapping, see the EclipseLink API Reference.

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