Specifying entity inheritance

An entity may inherit properties from other entities. You can specify a specific strategy to use for inheritance.

Use this procedure to specify inheritance (@Inheritance) for an existing entity (@Entity):

1. Select the entity in the Package Explorer.

2. In the JPA Details view, select the Inheritance information.

   Specifying Inheritance

   
   

3. In the Strategy list, select one of the following the inheritance strategies:

   • A single table (default)

   • Joined table

   • One table per class

4. Use the following table to complete the remaining fields on the tab. See "Inheritance information" for additional details.

   Property	Description	Default
   Discriminator Column	Name of the discriminator column when using a Single or Joined inheritance strategy. This field corresponds to the @DiscriminatorColumn annotation.
   Discriminator Type	Set the discriminator type to Char or Integer (instead of its default: String). The Discriminator Value must conform to this type.	String
   Discriminator Value	Specify the discriminator value used to differentiate an entity in this inheritance hierarchy. The value must conform to the specified Discriminator Type. This field corresponds to the @DiscriminatorValue annotation.
   Override Default	Use this field to specify custom primary key join columns. This field corresponds to the @PrimaryKeyJoinClumn annotation.

   
   

Eclipse adds the following annotations the entity field:

@Inheritance(strategy=InheritanceType.<INHERITANCE_STRATEGY>)
@DiscriminatorColumn(name="<DISCRIMINATOR_COLUMN>",
    discriminatorType=<DISCRIMINATOR_TYPE>)
@DiscriminatorValue(value-"<DISCRIMINATOR_VALUE>")
@PrimaryKeyJoinColumn(name="<JOIN_COLUMN_NAME>", 
    referencedColumnName = "<REFERENCED_COLUMN_NAME>")

The following figures illustrates the different inheritance strategies.

 

Adding persistence to a class

 

Understanding Java persistence