Package org.hibernate.id

Class SelectGenerator

java.lang.Object

org.hibernate.id.SelectGenerator

All Implemented Interfaces:

Serializable, Generator, OnExecutionGenerator, BulkInsertionCapableIdentifierGenerator, Configurable, StandardGenerator, PostInsertIdentifierGenerator

public class SelectGenerator
extends Object
implements PostInsertIdentifierGenerator, BulkInsertionCapableIdentifierGenerator, StandardGenerator

A generator that selects the just-inserted row to determine the column value assigned by the database. The correct row is located using a unique key of the entity, either:

• the mapped NaturalId of the entity, or
• a property specified using the parameter named "key".

The second approach is provided for backward compatibility with older versions of Hibernate.

This generator is intended for use with primary keys assigned by a database trigger or something similar, for example:

 @Entity @Table(name="TableWithPKAssignedByTrigger")
 @GenericGenerator(name = "triggered", type = SelectGenerator.class)
 public class TriggeredEntity {
     @Id @GeneratedValue(generator = "triggered")
     private Long id;

     @NaturalId
     private String name;

     ...
 }
 

However, after a very long working life, this generator is now handing over its work to GeneratedGeneration, and the above code may be written as:

 @Entity @Table(name="TableWithPKAssignedByTrigger")
 public class TriggeredEntity {
     @Id @Generated
     private Long id;

     @NaturalId
     private String name;

     ...
 }
 

For tables with identity/autoincrement columns, use IdentityGenerator.

The actual work involved in retrieving the primary key value is the job of UniqueKeySelectingDelegate.

Arguably, this class breaks the natural separation of responsibility between the generator and the coordinating code, since its role is to specify how the generated value is retrieved.

Author:

Gavin King

See Also:

• NaturalId
• UniqueKeySelectingDelegate
• Serialized Form

Field Summary

Fields

Modifier and Type	Field	Description
static final String	KEY	The property specifying the unique key name.

Constructor Summary

Constructors

Constructor	Description
SelectGenerator()

Method Summary

Modifier and Type	Method	Description
void	configure(Type type, Properties parameters, ServiceRegistry serviceRegistry)	Noop default implementation.
String[]	getReferencedColumnValues(Dialect dialect)	A SQL expression indicating how to calculate the generated values when the mapped columns are included in the SQL statement.
String[]	getUniqueKeyPropertyNames(EntityPersister persister)	The name of a property of the entity which may be used to locate the just-inserted row containing the generated value.
boolean	referenceColumnsInSql(Dialect dialect)	Determines if the columns whose values are generated are included in the column list of the SQL insert or update statement.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface org.hibernate.id.BulkInsertionCapableIdentifierGenerator

determineBulkInsertionIdentifierGenerationSelectFragment, supportsBulkInsertionIdentifierGeneration

Methods inherited from interface org.hibernate.id.Configurable

create, initialize

Methods inherited from interface org.hibernate.generator.Generator

allowAssignedIdentifiers, generatedOnExecution, generatesOnInsert, generatesOnUpdate, generatesSometimes

Methods inherited from interface org.hibernate.generator.OnExecutionGenerator

generatedOnExecution, getGeneratedIdentifierDelegate

Methods inherited from interface org.hibernate.id.PostInsertIdentifierGenerator

getEventTypes, writePropertyValue

Field Details

KEY

public static final String KEY

The property specifying the unique key name.

See Also:

• Constant Field Values

Constructor Details

SelectGenerator

public SelectGenerator()

Method Details

configure

public void configure(Type type,
 Properties parameters,
 ServiceRegistry serviceRegistry)

Description copied from interface: PostInsertIdentifierGenerator

Noop default implementation. May be overridden by subtypes.

Specified by:

configure in interface Configurable

Specified by:

configure in interface PostInsertIdentifierGenerator

Parameters:

type - The id property type descriptor

parameters - param values, keyed by parameter name

serviceRegistry - Access to service that may be needed.

getUniqueKeyPropertyNames

public String[] getUniqueKeyPropertyNames(EntityPersister persister)

Description copied from interface: OnExecutionGenerator

The name of a property of the entity which may be used to locate the just-inserted row containing the generated value. Of course, the columns mapped by this property should form a unique key of the entity.

The default implementation uses the @NaturalId property, if there is one.

Specified by:

getUniqueKeyPropertyNames in interface OnExecutionGenerator

referenceColumnsInSql

public boolean referenceColumnsInSql(Dialect dialect)

Description copied from interface: OnExecutionGenerator

Determines if the columns whose values are generated are included in the column list of the SQL insert or update statement. For example, this method should return:

• true if the value is generated by calling a SQL function like current_timestamp, or
• false if the value is generated by a trigger, by generated always as, or using a column default value.

Specified by:

referenceColumnsInSql in interface OnExecutionGenerator

Returns:

true if the column is included in the column list of the SQL statement.

getReferencedColumnValues

public String[] getReferencedColumnValues(Dialect dialect)

Description copied from interface: OnExecutionGenerator

A SQL expression indicating how to calculate the generated values when the mapped columns are included in the SQL statement. The SQL expressions might be:

• function calls like current_timestamp or nextval('mysequence'), or
• syntactic markers like default.

Specified by:

getReferencedColumnValues in interface OnExecutionGenerator

Parameters:

dialect - The SQL dialect, allowing generation of an expression in dialect-specific SQL.

Returns:

The column value to be used in the generated SQL statement.