The <generator> class is a sub-element of id. It is used to generate the unique identifier for the objects of persistent class. There are many generator classes defined in the Hibernate Framework.
I have a composite key with 2 fields. 1 field is an auto-incrementing field, the other is a foreign key. I've been trying to put @GeneratedValue annotation on the auto-incrementing field, but can't seem to get it to work properly. Is this supported? I assumed thats why it was broken out of the @ID annotation so that it could be used on any field. Jan 06, 2007 Hibernate Community Forums. Hi, I have table with composite primary key and I created following mapping for the table.As it is possible to insert a null value for any column in composite key as long as the combination of all columns is Unique, I have record in teh table which has null value for VCHAR2 column ( which is part of composite key ). When I execute a query on this entity I get null. Aug 01, 2016 Introduction One of my readers asked me to help him map a Composite Primary Key using JPA and Hibernate. Because this is a recurrent question, I decided to write a blog post in which I describe this mapping is more detail. Domain Model A relational database composite key contains two or more columns which together for the primary key of a given table. In the diagram above, the employee table. Aug 05, 2012 'I have a composite key where one column holds a generated value - how can I get Hibernate to generate and assign the value? We regard this as an extremely strange thing to want to do. If you have a generated surrogate key, why not just make it be the primary key? You can use them to generate unique primary key values, to map and create UUIDs, to work with composite primary keys, and to use the same primary key value for associated entities. And Hibernate also supports natural primary keys with its own, proprietary query mechanism.
All the generator classes implements the org.hibernate.id.IdentifierGenerator interface. The application programmer may create one's own generator classes by implementing the IdentifierGenerator interface. Hibernate framework provides many built-in generator classes:
1) assigned
It is the default generator strategy if there is no <generator> element . In this case, application assigns the id. For example:
2) increment
It generates the unique id only if no other process is inserting data into this table. It generates short, int or long type identifier. If a table contains an identifier then the application considers its maximum value else the application consider that the first generated identifier is 1. For each attribute value, the hibernate increment the identifier by 1. Syntax:
3) sequence
It uses the sequence of the database. if there is no sequence defined, it creates a sequence automatically e.g. in case of Oracle database, it creates a sequence named HIBERNATE_SEQUENCE. In case of Oracle, DB2, SAP DB, Postgre SQL or McKoi, it uses sequence but it uses generator in interbase. Syntax:
For defining your own sequence, use the param subelement of generator.
4) hilo
It uses high and low algorithm to generate the id of type short, int and long. Syntax:
5) native
It uses identity, sequence or hilo depending on the database vendor. Syntax:
6) identity
It is used in Sybase, My SQL, MS SQL Server, DB2 and HypersonicSQL to support the id column. The returned id is of type short, int or long. It is responsibility of database to generate unique identifier.
7) seqhiloHibernate Composite Key Generated Value List
It uses high and low algorithm on the specified sequence name. The returned id is of type short, int or long.
8) uuid
It uses 128-bit UUID algorithm to generate the id. The returned id is of type String, unique within a network (because IP is used). The UUID is represented in hexadecimal digits, 32 in length.
9) guid
10) select
Hibernate Composite Key Generated Value Chart11) foreignHibernate Composite Key Generated Value Calculator
12) sequence-identityHibernate Composite Key Generated Value List
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