Package org.hibernate.id

Class IdentityGenerator

java.lang.Object

org.hibernate.id.IdentityGenerator

All Implemented Interfaces:

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

public class IdentityGenerator
extends Object
implements PostInsertIdentifierGenerator, BulkInsertionCapableIdentifierGenerator, StandardGenerator

An OnExecutionGenerator that handles IDENTITY/"autoincrement" columns on those databases which support them.

Delegates to the IdentityColumnSupport provided by the dialect.

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

See Also:

GenerationType.IDENTITY, IdentityColumnSupport, GeneratedValuesMutationDelegate, Serialized Form

Implementation Note:

This also implements the identity generation type in hbm.xml mappings.

Constructor Summary

Constructors

Constructor	Description
IdentityGenerator()

Method Summary

Modifier and Type	Method	Description
InsertGeneratedIdentifierDelegate	getGeneratedIdentifierDelegate(PostInsertIdentityPersister persister)	The InsertGeneratedIdentifierDelegate used to retrieve the generated value if this object is an identifier generator.
String[]	getReferencedColumnValues(Dialect dialect)	A SQL expression indicating how to calculate the generated values when the mapped columns are included in the SQL statement.
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, getUniqueKeyPropertyNames

Methods inherited from interface org.hibernate.id.PostInsertIdentifierGenerator

configure, getEventTypes, writePropertyValue

Constructor Detail

IdentityGenerator

public IdentityGenerator()

Method Detail

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.

getGeneratedIdentifierDelegate

public InsertGeneratedIdentifierDelegate getGeneratedIdentifierDelegate(PostInsertIdentityPersister persister)

Description copied from interface: OnExecutionGenerator

The InsertGeneratedIdentifierDelegate used to retrieve the generated value if this object is an identifier generator.

This is ignored by GeneratedValuesProcessor, which handles multiple generators at once. So if this object is not an identifier generator, this method is never called.

Note that this method arguably breaks the separation of concerns between the generator and coordinating code, by specifying how the generated value should be retrieved.

The problem solved here is: we want to obtain an insert-generated primary key. But, sadly, without already knowing the primary key, there's no completely-generic way to locate the just-inserted row to obtain it.

We need one of the following things:

• a database which supports some form of insert ... returning syntax, or can do the same thing using the JDBC getGeneratedKeys() API, or
• a second unique key of the entity, that is, a property annotated @NaturalId.

Alternatively, if the generated id is an identity/"autoincrement" column, we can take advantage of special platform-specific functionality to retrieve it. Taking advantage of the specialness of identity columns is the job of one particular implementation: IdentityGenerator. And the need for customized behavior for identity columns is the reason why this layer-breaking method exists.

Specified by:

getGeneratedIdentifierDelegate in interface OnExecutionGenerator