How can composite primary keys be used to manage data versions in JPA?

Creating and Handling Composite Primary Key in JPA

To manage data versions within an entity, creating a composite primary key allows for the duplication of entries based on version numbers. Consider the following implementation:

@Entity
public class YourEntity {
    @EmbeddedId
    private MyKey id;
    private String columnA;
    // Getters and setters omitted for brevity
}

@Embeddable
public class MyKey implements Serializable {
    private int id;
    private int version;
    // Getters and setters omitted for brevity
}

Using this approach, both id and version fields form the composite primary key. This enables the creation of multiple versions for each data record:

Entity 1: id = 1, version = 0, columnA = "Data Entry 1"
Entity 2: id = 1, version = 1, columnA = "Updated Data Entry 1"

An alternative method to define a composite primary key is using the @IdClass annotation:

@Entity
@IdClass(MyKey.class)
public class YourEntity {
    @Id
    private int id;
    @Id
    private int version;
    private String columnA;
    // Getters and setters omitted for brevity
}

public class MyKey implements Serializable {
    private int id;
    private int version;
    // Getters and setters omitted for brevity
}

In this case, the MyKey class serves as the primary key class, and the id and version fields within it are both annotated with @Id.

By utilizing either the @EmbeddedId or @IdClass annotations, JPA can effectively manage composite primary keys, facilitating the storage and retrieval of data versions within a single entity.

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