Auto Generated Primary Key In Jpa

  1. Unique Key
  2. Auto Generated Primary Key In Jpa 2018
  3. Primary Key Adalah
  4. Auto Generated Primary Key In Jpa 2017
  5. Auto Generated Primary Key In Jpa Texas
  6. Auto Generated Primary Key Jpa
  7. Auto Generated Primary Key In Oracle

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 columns.

Supported types for a primary key

A simple primary key field or one of the composite primary key field should be one of the following types:

You can read more about the different strategies to generate unique primary key values in: How To Generate Primary Keys With JPA And Hibernate; How To Generate UUIDs As Primary Keys; And if you want to learn more database-specific mapping and query features, you should take a look at: 5 Things You Need To Know When Using Hibernate With MySQL. Aug 19, 2015 It will be good if we could generate values for non- @id columns via standard JPA annotations, simply because not only the @id columns might require custom value generation. May be in JPA we could have separate annotations just like @GeneratorType and @ValueGenerationType in Hibernate, which allows generation of values for non-@id columns. Aug 02, 2014  There are two widely known methods to perform the generation of primary key values on the database level: auto-increment/identity columns or sequences. Due to these differences JPA provide three different ways to automatically generate primary key values. Let’s explore them below. Using auto-increment/identity columns.

I'm using hibernate as jpa provider, and I have a table that has some columns that are generated values (using a sequence), although they are not part of the identifier. What I want is to use a sequence to create a new value for an entity, where the column for the sequence is NOT (part of) the primary key. Primary key value generation strategy JPA ( Hibernate ) Generated identifiers are indicated by @javax.persistence.GeneratedValue as discussed above. There are basically 4 strategies to generate values of id fields. These are AUTO, IDENTITY, SEQUENCE and TABLE. Package javax.persistence; /. Defines the types of primary key generation strategies.

  • Any Java primitive type
  • any Any primitive wrapper type
  • java.lang.String
  • java.util.Date
  • java.sql.Date
  • java.math.BigDecimal
  • java.math.BigInteger

In this tutorial we are going to focus on generation strategies of simple primary key.

@GeneratedValue Annotation

This annotation defines the types of primary key generation strategies. If this annotation is not used then application is responsible to populate and manage @Id field values itself.

The use of the GeneratedValue annotation is only required to be supported for simple primary keys.

Unique Key

GenerationType enum defines four strategies: Generation Type . TABLE, Generation Type. SEQUENCE, Generation Type. IDENTITY and Generation Type. AUTO. Let's understand them with examples.

GenerationType.SEQUENCE

With this strategy, underlying persistence provider must use a database sequence to get the next unique primary key for the entities.

We have created the following Util class to reuse the code for other examples.

Also, in the persistence.xml, we have created four persistence-unit, so that we can try four GenerationType independently. We are using Hibernate as persistence provider.

Let's create main class to try out Entity1 key generation.

Output

Above output shows one table MYENTITY1 and one sequence HIBERNATE_SEQUENCE are created.

GenerationType.TABLE

With this strategy, underlying persistence provider must use a database table to generate/keep the next unique primary key for the entities.

Output

This time no sequence is generated, instead an additional table named 'HIBERNATE_SEQUENCES' is created to maintain primary key sequence.

GenerationType.IDENTITY

This GenerationType indicates that the persistence provider must assign primary keys for the entity using a database identity column. IDENTITY column is typically used in SQL Server. This special type column is populated internally by the table itself without using a separate sequence. If underlying database doesn't support IDENTITY column or some similar variant then the persistence provider can choose an alternative appropriate strategy. In this examples we are using H2 database which doesn't support IDENTITY column.

Output

Above output shows that a sequence is used for primary keys.

GenerationType.AUTO

This GenerationType indicates that the persistence provider should automatically pick an appropriate strategy for the particular database. This is the default GenerationType, i.e. if we just use @GeneratedValue annotation then this value of GenerationType will be used.

Output

Above output shows that a sequence is used for primary keys.

When @GeneratedValue not used

If we don't use @GeneratedValue annotation at all, then we have to populate the unique primary keys ourselves. In this example, we are simply assigning it to the value returned from System.nanoTime()

Output

Above output shows that a no sequence or extra table were generated.

Example Project

Dependencies and Technologies Used:

  • h2 1.4.193: H2 Database Engine.
  • hibernate-core 5.2.8.Final: The core O/RM functionality as provided by Hibernate.
    Implements javax.persistence:javax.persistence-api version 2.1
  • JDK 1.8
  • Maven 3.3.9

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#id

Using 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 equals and hashCode methods.

    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.

Auto Generated Primary Key In Jpa 2018

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

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Primary Key Adalah

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.

Table 7-2 lists the types of primary key value generators that you can define.

Table 7-2 JPA Entity Primary Key Value Generators

TypeDescriptionFor 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:

Auto Generated Primary Key In Jpa 2017

For an EJB 3.0 automatic primary key generation code example, see: http://www.oracle.com/technology/tech/java/oc4j/ejb3/howtos-ejb3/howtoejb30mappingannotations/doc/how-to-ejb30-mapping-annotations.html#sequencing

Using Annotations

Auto Generated Primary Key In Jpa Texas

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

Auto Generated Primary Key Jpa

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

Auto Generated Primary Key In Oracle

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.