DiscriminatorColumn (Java EE 5 SDK)

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Java EE 5 SDK

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摘要: REQUIRED | OPTIONAL

详细信息: ELEMENT

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

Optional Element Summary
`String`	`columnDefinition` (Optional) The SQL fragment that is used when generating the DDL for the discriminator column.
`DiscriminatorType`	`discriminatorType` (Optional) The type of object/column to use as a class discriminator.
`int`	`length` (Optional) The column length for String-based discriminator types.
`String`	`name` (Optional) The name of column to be used for the discriminator.

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

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