JPA composite primary key

Question

I have the following classes in my JPA model (getters, setters, and irrelevant fields omitted):

@Entity @Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public class Currency {

    @Id
    private Integer ix;
}

@Entity @Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public class Product {

    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;
}

I need to define a class Price, such that when the DDL is generated from the classes, the primary key of the corresponding table is composed of the keys for Product and Currency. I've tried the following:

@Entity @Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
@IdClass(PricePK.class)
public class Price {

    @Id @ManyToOne(optional = false)
    private Product product;

    @Id
    @ManyToOne(optional = false)
    private Currency currency;
}

@Embeddable
public class PricePK implements Serializable {

    Integer product;        
    Integer currency;
}

But this generates the following for the PRICE table:

create table PRICE (
    currency_id int null,
    product_id int null,
    primary key (currency_id, product_id)
);

Notice that both currency_id and product_id are nullable, which causes the following error when I try to load the DDL into SQL Server

Cannot define PRIMARY KEY constraint on nullable column in table 'PRICE'

I don't understand why these are nullable, because in the domain model they are annotated @ManyToOne(optional = false)

The DDL is generated using the org.hibernate.dialect.SQLServerDialect SQL dialect.

Answer 1

Recently I created ManyToMany relation using Composite Primary key and annotation as bi directional @OneToMany. This code works flawless. Maybe it will help:

Mapping ManyToMany with composite Primary key and Annotation:

Answer 2

Since you are using @IdClass, the PricePK class need not be marked with the @Embeddable annotation. An example is given in http://www.java2s.com/Code/Java/JPA/SetIdClassforCompoundKey.htm

I tried your code removing the @Embeddable on PricePK class, and the price table generated in MYSQL database with not null fields.

Following is how you could use @EmbeddedId to achieve the required result: (getters and setters omitted)

@Entity
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public class Price {

    @EmbeddedId
    PricePK pricePk;
}

@Embeddable
public class PricePK implements Serializable {

    @ManyToOne(optional = false)
    private Product product;

    @ManyToOne(optional = false)
    private Currency currency;
}