Specify Generated Value Of Composite Primary Keys In Jpa

Specify Generated Value Of Composite Primary Keys In Jpa Average ratng: 8,3/10 5997 reviews

An entity may have either a simple or a composite primary key. Simple primary keys use the javax.persistence.Id annotation to denote the primary key property or field. Composite primary keys are used when a primary key consists of more than one attribute, which corresponds to a set of single persistent properties or fields. How to create and handle composite primary key in JPA. Explicitly set the value for them in your KeyClass instance, and then set that key class instance in your. Nov 23, 2017 If I specify the ID for the POJO (using setId(Long id)) and persist it, EclipseLink does not save it (i.e. The record is saved, but the id is auto generated by eclipseLink). Is there a way to manually specify the value of a column which has a @GeneratedValue? Here some thoughts on the issue. Mar 06, 2017  If a database table has more than one column as the primary key then we call it as composite primary key.In this Hibernate Composite Primary Key tutorial, we will learn how to define Composite Primary Key using tag and Annotations. Hibernate Composite Primary Key Tutorial Creating table. Create EMPLOYEE Table, simply Copy and Paste the following SQL query in the. Composite primary keys are used when a primary key consists of more than one attribute, which corresponds to a set of single persistent properties or fields. Composite primary keys must be defined in a primary key class. Composite primary keys are denoted using the javax.persistence.EmbeddedId and javax.persistence.IdClass annotations. In this article, we’ll learn how to use Composite Primary Key and the corresponding annotations in JPA. A composite primary key is formed by the combination of two or more java types and it is mapped to corresponding columns in the database.

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:

  • 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.

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.

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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. /ibm-spss-19-license-key-generator.html.

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.

Specify Generated Value Of Composite Primary Keys In Jpa 2016

Example Project

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Dependencies and Technologies Used:

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  • 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

Foreign Keys