Spring JPA, OneToMany referencing part of primary key

Question

Given A class

@Entity
@Table(name = "ATABLE")
public class A implements Serializable {
    public static final String DB_ID = "AID";
    public static final String DB_MARKET = "AMARKET";

    @EmbeddedId
    @AttributeOverrides({
            @AttributeOverride(name = "id", column = @Column(name = DB_ID)),
            @AttributeOverride(name = "market", column = @Column(name = DB_MARKET))
    })
    public AIdClass id;

    @OneToMany
    @JoinColumn(name = B.DB_MARKET, referencedColumnName = DB_MARKET, insertable = false, updatable = false)
    public List<B> bs;
}

and B class

@Entity
@Table(name = "BTABLE")
public class B implements Serializable {
    public static final String DB_ID = "BID";
    public static final String DB_MARKET = "BMARKET";

    @EmbeddedId
    @AttributeOverrides({
            @AttributeOverride(name = "id", column = @Column(name = DB_ID)),
            @AttributeOverride(name = "market", column = @Column(name = DB_MARKET))
    })
    public BIdClass id;
}

Each entities might be listed, but using that @OneToMany relation does throw the following error

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'entityManagerFactory'
Caused by: org.hibernate.AnnotationException: Unable to map collection fr.zzz.domain.A.bs
Caused by: org.hibernate.AnnotationException: referencedColumnNames(AMARKET) of fr.zzz.domain.A.bs referencing fr.zzz.domain.B not mapped to a single property

An A entity relates to multiple B on A.AMARKET = B.BMARKET

Answer 1

You are having this issue because there is be a possibility that composite keys (AID,AMARKET) and (BID,BMARKET) will not be unique when doing a join on keys AMARKET = BMARKET. Therefore you are getting the error not mapped to a single property. Please bear with me, use the following sample data to analyze the issue;

For table A

AID  AMARKET 
 1      1       
 2      1    
 3      2 

For table B

BID  BMARKET
 1      1   
 2      2
 3      2

The above scenario is absolutely possible (at least on a database level) and just using AMARKET and BMARKET to make the join @OneToMany is not possible. What is possible though is to use @ManyToMany, this will immediately solve the issue if the table structures are correct.

But what if it is required to use @OneToMany due to some business constraint. Then you must update the table B to include A.AID and add a foreign key constraint to ensure data integrity. Then only the result set will be valid for the relationship @OneToMany. And the join will be as follows;

@OneToMany
@JoinColumn(name = B.DB_AID, referencedColumnName = DB_ID)
@JoinColumn(name = B.DB_MARKET, referencedColumnName = DB_MARKET)
public List<B> bs;

In B:

@Entity
@Table(name = "BTABLE")
public class B implements Serializable {
    public static final String DB_ID = "BID";
    public static final String DB_MARKET = "BMARKET";
    public static final String DB_AID = "AID";

    @EmbeddedId
    @AttributeOverrides({
            @AttributeOverride(name = "id", column = @Column(name = DB_ID)),
            @AttributeOverride(name = "market", column = @Column(name = DB_MARKET))
    })
    public BIdClass id;

    @Column(name = DB_AID)
    private Long aid; // assuming aid is a Long
}

Now the join is being done on the composite primary key of A.