Identity Generators in Hibernate

 

Generator Description
increment It generates identifiers of type long, short or int that are unique only when no other process is inserting data into the same table. It should not the used in the clustered environment.
identity It supports identity columns in DB2, MySQL, MS SQL Server, Sybase and HypersonicSQL. The returned identifier is of type long, short or int.
sequence The sequence generator uses a sequence in DB2, PostgreSQL, Oracle, SAP DB, McKoi or a generator in Interbase. The returned identifier is of type long, short or int
hilo The hilo generator uses a hi/lo algorithm to efficiently generate identifiers of type long, short or int, given a table and column (by default hibernate_unique_key and next_hi respectively) as a source of hi values. The hi/lo algorithm generates identifiers that are unique only for a particular database. Do not use this generator with connections enlisted with JTA or with a user-supplied connection.
seqhilo The seqhilo generator uses a hi/lo algorithm to efficiently generate identifiers of type long, short or int, given a named database sequence.
uuid The uuid generator uses a 128-bit UUID algorithm to generate identifiers of type string, unique within a network (the IP address is used). The UUID is encoded as a string of hexadecimal digits of length 32.
guid It uses a database-generated GUID string on MS SQL Server and MySQL.
native It picks identity, sequence or hilo depending upon the capabilities of the underlying database.
assigned lets the application to assign an identifier to the object before save() is called. This is the default strategy if no <generator> element is specified.
select retrieves a primary key assigned by a database trigger by selecting the row by some unique key and retrieving the primary key value.
foreign uses the identifier of another associated object. Usually used in conjunction with a <one-to-one> primary key association.

  

JPA Annotations

AUTO Either identity column, sequence or table depending on the underlying DB  
@Id
@GeneratedValue( strategy = GenerationType.AUTO, generator = “userSeq” )
@SequenceGenerator( name = “userSeq”, sequenceName = “USER_DETAILS_SEQ” )
private Long id; 
TABLE Table holding the id 
<table-generator name=”EMP_GEN”  table=”GENERATOR_TABLE”

   pk-column-name=”key”
            value-column-name=”hi”
            pk-column-value=”EMP”
            allocation-size=”20″/>
//and the annotation equivalent
@javax.persistence.TableGenerator( name=”EMP_GEN”,    table=”GENERATOR_TABLE”,  pkColumnName = “key”, 
valueColumnName = “hi”, 
pkColumnValue=”EMP”,  allocationSize=20) 
IDENTITY Identity column

@Id

@Column( name = “ID”, nullable = false )

@GeneratedValue( strategy = GenerationType.IDENTITY)

private Long id;

SEQUENCE

<sequence-generator name=”SEQ_GEN” sequence-name=”my_sequence”
allocation-size=”20″/>
//and the annotation equivalent
@javax.persistence.SequenceGenerator(name=”SEQ_GEN”,sequenceName=”my_sequence”,
allocationSize=20)

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: