SQL JPA - Multiple columns as primary key

Question

If i want severeal Column to make up an ID.

SQL example :

CONSTRAINT [PK_NAME] PRIMARY KEY ([Column1],[Column2],[Column3])

How can i do that with a Jpa Entity class ? through columndefinition ?

just setting the id field as:

value = Column1 + Column2 + Column3 // aint working.

score 126 · Accepted Answer · edited Dec 25 '22 at 22:19

126

You need to have a class for your composite key:

public class CompositeKey implements Serializable {
    private int column1;
    private int column2;
    private int column3;
}

and then in your entity class use the @IdClass annotation:

@Entity
@IdClass(CompositeKey.class)
public class EntityExample {
    @Id
    private int column1;
    @Id
    private int column2;
    @Id
    private int column3;
    ...
    ...
}

I think this should work.

There is also the other solution that @jklee mentioned. Both work, it's a matter of preference.

edited Dec 25 '22 at 22:19

starball

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answered Dec 14 '16 at 13:41

Raul Cuth

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5

Note that there is a requirement to implement equals / hashCode (see https://docs.jboss.org/hibernate/orm/5.4/userguide/html_single/Hibernate_User_Guide.html#identifiers-composite) – PresentProgrammer Apr 08 '20 at 17:20
How would the `EntityExampleRepository extends JpaRepository< EntityExample, ???>` look like in this case? – Prasannjeet Singh Jul 31 '23 at 17:08

score 27 · Answer 2 · edited Mar 02 '22 at 09:07

27

Use @Embeddable and @EmbeddedId.

Example:

@Entity
public class Project implements Serializable {
    @EmbeddedId ProjectId id;
}
 
@Embeddable
class ProjectId implements Serializable {
    int departmentId;
    long projectId;
}

More information here http://www.objectdb.com/java/jpa/entity/id#Embedded_Primary_Key_

edited Mar 02 '22 at 09:07

lorraine batol

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answered Dec 14 '16 at 13:42

jklee

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Do not forget to implement Serializable ;-) – Diego Souza Jan 08 '20 at 23:56

score 23 · Answer 3 · answered Aug 09 '18 at 09:42

23

If all fields in the class are part of primary key, then solution would be pretty simple (extending solution provided by @raul-cuth):

@Entity
@IdClass(EntityExample.class)
public class EntityExample implements Serializable {

    @Id
    private int column1;

    @Id
    private int column2;

    @Id
    private int column3;
}

answered Aug 09 '18 at 09:42

heroin

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What if one of the fields is a FK? It would be a typical scenario when mapping a many-to-many *relationship* table. – Paulo Merson Dec 13 '22 at 18:28

score 4 · Answer 4 · edited Dec 14 '16 at 13:44

4

Using @IdClass annotation on the @Entity class followed by @Id annotation on individual fields that are part of composite primary key.
Alternatively can make use of @Embeddable class which can consist of individual fields of the composite primary key and then a reference of this class can be used as an attribute with @Embedded annotation in @Entity class. Hope this helps.

edited Dec 14 '16 at 13:44

M. Deinum

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answered Dec 14 '16 at 13:42

Penguin

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score 2 · Answer 5 · answered Oct 11 '19 at 20:27

Be aware that the hibernate Entity-Class-to-SQL-DDL-Script generator will sort all the fields, and irrespective of the order in which it appears in the definitions, will create the table definition and the index / constraint definitions in this sorted order of the fields.

While the order of appearance of the fields in the table definition may not matter much, the order of fields in a composite index definitely do. So your key-fields must be named so that when sorted by their names they are in the order you desire for the index).

SQL JPA - Multiple columns as primary key

5 Answers5

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