@ExistenceChecking

Use @ExistenceChecking to specify how TopLink should check to determine if an entity is new or exists.

On merge() operations, use @ExistenceChecking to specify if TopLink uses only the cache to determine if an object exists, or if the object should be read (from the database or cache). By default the object will be read from the database.

Annotation Elements

Table 2-20 describes this annotation's elements.

Table 2-20 @ExistenceChecking Annotation Elements

Annotation Element Description Default

Annotation Element	Description	Default
`ExistenceType`	(Optional) Set the existence checking type: `ASSUME_EXISTENCE` `ASSUME_NON_EXISTENCE` `CHECK_CHACHE` `CHECK_DATABASE`	`CHECK_CACHE`

ExistenceType

(Optional) Set the existence checking type:

ASSUME_EXISTENCE
ASSUME_NON_EXISTENCE
CHECK_CHACHE
CHECK_DATABASE

CHECK_CACHE

Usage

You can specify @ExistenceChecking on an Entity or MappedSuperclass.

EclipseLink supports the following existence checking types:

ASSUME_EXISTENCE – If the object's primary key does not include null then it must exist. You may use this option if the application guarantees or does not care about the existence check.
ASSUME_NON_EXISTENCE – Assume that the object does not exist. You may use this option if the application guarantees or does not care about the existence check. This will always force an INSERT operation.
CHECK_CHACHE – If the object's primary key does not include null and it is in the cache, then it must exist.
CHECK_DATABASE – Perform a SELECT on the database.

Examples

Example 2-41 shows how to use this annotation.

Example 2-41 Using @ExistenceChecking Annotation

@Entity
@Cache(type=CacheType.HARD_WEAK,  expiryTimeOfDay=@TimeOfDay(hour=1))
@ExistenceChecking(ExistenceType.CHECK_DATABASE)
public  class  Employee  implements  Serializable  { 
...
}