DiscriminatorColumn (Java EE 5 SDK)

javax.persistence Annotation Type DiscriminatorColumn

@Target(value=TYPE)
@Retention(value=RUNTIME)
public @interface DiscriminatorColumn

Is used to define the discriminator column for the SINGLE_TABLE and JOINED inheritance mapping strategies.

The strategy and the discriminator column are only specified in the root of an entity class hierarchy or subhierarchy in which a different inheritance strategy is applied

If the DiscriminatorColumn annotation is missing, and a discriminator column is required, the name of the discriminator column defaults to "DTYPE" and the discriminator type to DiscriminatorType.STRING.

     Example:
     @Entity
     @Table(name="CUST")
     @Inheritance(strategy=SINGLE_TABLE)
     @DiscriminatorColumn(name="DISC", discriminatorType=STRING,length=20)
     public class Customer { ... }

     @Entity
     public class ValuedCustomer extends Customer { ... }
 

从以下版本开始:

Java Persistence 1.0

name

public abstract String name

(Optional) The name of column to be used for the discriminator.

默认值:

"DTYPE"

discriminatorType

public abstract DiscriminatorType discriminatorType

(Optional) The type of object/column to use as a class discriminator. Defaults to DiscriminatorType.STRING.

默认值:

STRING

columnDefinition

public abstract String columnDefinition

(Optional) The SQL fragment that is used when generating the DDL for the discriminator column.

Defaults to the provider-generated SQL to create a column of the specified discriminator type.

默认值:

""

length

public abstract int length

(Optional) The column length for String-based discriminator types. Ignored for other discriminator types.

默认值:

31

版权所有 2007 Sun Microsystems, Inc. 保留所有权利。 请遵守许可证条款。深圳电信培训中心.徐海蛟老师教学参考.