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

Answer 1

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).

Answer 2

1. Using @IdClass annotation on the @Entity class followed by @Id annotation on individual fields that are part of composite primary key.
2. 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.

Answer 3

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 4

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;
}

Answer 5

Use @Embeddable and @EmbeddedId.

Example:

@Entity
public class Project {
    @EmbeddedId ProjectId id;
     :
}

@Embeddable
Class ProjectId {
    int departmentId;
    long projectId;
}

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