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. 

Answer 1

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. Hope it helps, cheers!

Yea and there is the other solution, the one that @jklee mentioned, both work, it's a matter of preference.

Answer 2

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_