Jpa Composite Key Auto Generated
- Sql Composite Key Example
- Definition Of Composite Key
- Example Of Composite Key
- Jpa Composite Key Auto Generated Key
Aug 02, 2014 Primary key generation in JPA Posted on August 2, 2014 by Robert Piasecki Generation of primary key values is a very important functionality of relational database management systems. Jan 07, 2020 And then add primary key constraint. ALTER TABLE autoincrementtb ADD ( CONSTRAINT autoincrementtbpk PRIMARY KEY (id) ); Now we will create a sequence to generate unique auto incremented values. A sequence is a data object that can be used by multiple users to generate auto increment values(no duplicate values will be generated). Configuring a JPA Entity Composite Primary Key Class. A composite primary key is usually made up of two or more primitive or JDK object types. Composite primary keys typically arise when mapping from legacy databases when the database key is comprised of several columns. You can specify such a composite primary key with a separate composite primary key class (see. Aug 08, 2017 Every JPA entity is required to have a field which maps to primary key of the database table. Such field must be annotated with @Id. Simple vs Composite primary keys. A simple primary key consists of a single Java field which maps to a single table column. A composite primary key consists of multiple Java fields which individually map to separate.
Every JPA entity must have a primary key.
You can specify a primary key as a single primitive, or JDK object type entity field (see 'Configuring a JPA Entity Simple Primary Key Field').
You can specify a composite primary key made up of one or more primitive, or JDK object types using a separate composite primary key class (see 'Configuring a JPA Entity Composite Primary Key Class').
You can either assign primary key values yourself, or you can associate a primary key field with a primary key value generator (see 'Configuring JPA Entity Automatic Primary Key Generation').
Configuring a JPA Entity Simple Primary Key Field
The simplest primary key is one you specify as a single primitive or JDK object type entity field (see 'Using Annotations').
Note:
For a JPA entity primary key field code example, see:http://www.oracle.com/technology/tech/java/oc4j/ejb3/howtos-ejb3/howtoejb30mappingannotations/doc/how-to-ejb30-mapping-annotations.html#idUsing Annotations
Example 7-1 shows how to use the @Id annotation to specify an entity field as the primary key. In this example, primary key values are generated using a table generator (see 'Configuring JPA Entity Automatic Primary Key Generation').
Configuring a JPA Entity Composite Primary Key Class
A composite primary key is usually made up of two or more primitive or JDK object types. Composite primary keys typically arise when mapping from legacy databases when the database key is comprised of several columns. You can specify such a composite primary key with a separate composite primary key class (see 'Using Annotations')
A composite primary key class has the following characteristics:
It is a POJO class.
It must be public and must have a public no-argument constructor.
If you use property-based access, the properties of the primary key class must be public or protected.
It must be serializable.
It must define
equalsandhashCodemethods.The semantics of value equality for these methods must be consistent with the database equality for the database types to which the key is mapped.
You can make the composite primary key class either an embedded class owned by the entity class, or a nonembedded class whose fields you map to multiple fields or properties of the entity class. In the latter case, the names of primary key fields or properties in the composite primary key class and those of the entity class must correspond and their types must be the same.
Using Annotations
Example 7-2 shows a typical embeddable composite primary key class. Example 7-3 shows how to configure a JPA entity with this embedded composite primary key class using the @EmbeddedId annotation.
Example 7-2 Embeddable Composite Primary Key Class
Example 7-3 JPA Entity With an Embedded Composite Primary Key Class
Example 7-5 shows a nonembedded composite primary key class. In this class, fields empName and birthDay must correspond in name and type to properties in the entity class. Example 7-5 shows how to configure a JPA entity with this nonembedded composite primary key class using the @IdClass annotation. Because entity class fields empName and birthDay are used in the primary key, you must also annotate them using the @Id annotation.
Example 7-4 Non-Embedded Composite Primary Key Class
Example 7-5 JPA Entity With a Mapped Composite Primary Key Class
Configuring JPA Entity Automatic Primary Key Generation
Typically, you associate a primary key field (see 'Configuring a JPA Entity Simple Primary Key Field') with a primary key value generator so that when an entity instance is created, a new, unique primary key value is assigned automatically.
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Table 7-2 lists the types of primary key value generators that you can define.
Table 7-2 JPA Entity Primary Key Value Generators
| Type | Description | For more information, see .. |
|---|---|---|
Generated Id Table | A database table that the container uses to store generated primary key values for entities. Typically shared by multiple entity types that use table-based primary key generation. Each entity type will typically use its own row in the table to generate the primary key values for that entity class. Primary key values are positive integers. | 'Table Sequencing' in the Oracle TopLink Developer's Guide |
Table Generator | A primary key generator, which you can reference by name, defined at one of the package, class, method, or field level. The level at which you define it will depend upon the desired visibility and sharing of the generator. No scoping or visibility rules are actually enforced. Oracle recommends that you define the generator at the level for which it will be used. This generator is based on a database table. | 'Table Sequencing' in the Oracle TopLink Developer's Guide |
Sequence Generator | A primary key generator which you can reference by name, defined at one of the package, class, method, or field level. The level, at which you define it, will depend upon the desired visibility and sharing of the generator. No scoping or visibility rules are actually enforced. Oracle recommends that you define the generator at the level for which it will be used. This generator is based on a sequence object that the database server provides. | 'Native Sequencing With an Oracle Database Platform' in the Oracle TopLink Developer's Guide 'Native Sequencing With a Non-Oracle Database Platform' in the Oracle TopLink Developer's Guide |
Note:
For an EJB 3.0 automatic primary key generation code example, see:Sql Composite Key Example
http://www.oracle.com/technology/tech/java/oc4j/ejb3/howtos-ejb3/howtoejb30mappingannotations/doc/how-to-ejb30-mapping-annotations.html#sequencingUsing Annotations
Example 7-6 shows how to use the @TableGenerator annotation to specify a primary key value generator based on a database table. The TopLink JPA persistence provider will attempt to create this table at deployment time: if it cannot, then you must follow your database documentation to ensure that this table exists before deployment. When a new instance of Address is created, a new value for entity field id is obtained from ADDRESS_GENERATOR_TABLE. In this case, you must set the @GeneratedValue annotation attribute strategy to TABLE and generator to ADDRESS_TABLE_GENERATOR.
Example 7-6 GeneratedValue Strategy Table: @TableGenerator
Example 7-7 shows how to use the @SequenceGenerator annotation to specify a primary key value generator based on a sequence object provided by the database. The TopLink JPA persistence provider will attempt to create this object at deployment time: if it cannot, then you must follow your database documentation to ensure that this sequence object exists before deployment. When a new instance of Address is created, a new value for entity field id is obtained from database sequence object ADDRESS_SEQ. In this case, you must set the @GeneratedValue annotation attribute strategy to SEQUENCE and generator to ADDRESS_SEQUENCE_GENERATOR.
Example 7-7 GeneratedValue Strategy Sequence: @SequenceGenerator
Example 7-8 shows how to use the @GeneratedValue annotation to specify a primary key value generator based on a primary key identity column (autonumber column). When a new instance of Address is persisted, the database assigns a value to the identity column. In this case, the TopLink JPA persistence provider re-reads the inserted row and updates the in-memory Address entity to set id to this value.
Definition Of Composite Key
Kundera allows you to store objects with generated primary key value in NoSQL. (Currently supported for MongoDB, HBase, Cassandra, Kudu and Redis).
To enable this feature, Entities must have @GeneratedValue annotation along with @Id annotation.
Kundera supports following types of generation strategies:
- AUTO
- SEQUENCE
- TABLE
AUTO generation strategy
Only supported for MongoDB, Kudu and Elasticsearch. To generate primary key using auto-generation strategy, id attribute in the entity must be of String type.
In order to use Auto-generation strategy, set strategy to GenerationType.AUTO. (This is default in case you don't specify any strategy).
SEQUENCE generation strategy
Only supported for Redis client. To generate primary key using Sequence generation strategy, Id attribute in the entity must be one of the java's numeric types.
In order to use Sequence-generation strategy, set strategy to GenerationType.SEQUENCE. Rest attributes are self-explanatory and have their meanings derived from JPA.
OR
TABLE generation strategy
Example Of Composite Key
Only supported for HBase and Cassandra clients. To generate primary key using Table generation strategy, Id attribute in the entity must be one of the java's numeric types.
In order to use Table-generation strategy, set strategy to GenerationType.TABLE. Rest attributes are self-explanatory and have their meanings derived from JPA.
OR
Identity generation strategy
Jpa Composite Key Auto Generated Key
This is currently not supported by Kundera.