EntityGraph or Join Fetch with Inheritance in JPA/Hibernate

Question

I am working on JPA/Hibernate entities with JpaRepositories. I have few entities with @OneToOne and @OneToMany relationships. To make code short and simple I have named entities as A, B, C, D etc.. A is the root entity and below chain there is Inheritance with Joined strategy. Please look code below -

A.java

@Entity
@Table(name = "A")
public class A {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long aId;

    @Column
    private String name;

    @OneToOne
    @JoinColumn(name = "bId")
    private B b;

    @OneToMany(mappedBy = "a")
    private Set<C> cSet;
    
    // other entity specific fields
    // getters and setters
}

B.java

@Entity
@Table(name = "B")
public class B {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long bId;

    // other entity specific fields
    // getters and setters
}

C.java

@Entity
@Table(name = "C")
public class C {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long cId;

    @ManyToOne
    @JoinColumn(name = "aId", referencedColumnName = "aId")
    private A a;

    @OneToMany(mappedBy = "c")
    private Set<D> dSet;

    // other entity specific fields
    // getters and setters
}

D.java

@Entity
@Table(name = "D")
@Inheritance(strategy = InheritanceType.JOINED)
public class D {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long dId;

    @ManyToOne
    @JoinColumn(name = "cId", referencedColumnName = "cId")
    private C c;

    @OneToMany(mappedBy = "d")
    private Set<E> eSet;

    // other entity specific fields
    // getters and setters

}

E.java

@Entity
@Table(name = "E")
public class E {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long eId;

    @ManyToOne
    @JoinColumn(name = "dId", referencedColumnName = "dId")
    private D d;

    // other entity specific fields
    // getters and setters
}

F.java

@Entity
@Table(name = "F")
public class F extends D {

    @OneToMany(mappedBy = "d")
    private Set<H> hSet;

    // other entity specific fields
    // getters and setters
}

G.java

@Entity
@Table(name = "G")
public class G extends D {

    @OneToMany(mappedBy = "d")
    private Set<I> iSet;

    // other entity specific fields
    // getters and setters
}

H.java

@Entity
@Table(name = "H")
public class H {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long hId;

    @ManyToOne
    @JoinColumn(name = "dId", referencedColumnName = "dId")
    private D d;

    // other entity specific fields
    // getters and setters
}

I.java

@Entity
@Table(name = "I")
public class I {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long iId;

    @ManyToOne
    @JoinColumn(name = "dId", referencedColumnName = "dId")
    private D d;

    // other entity specific fields
    // getters and setters
}

If you see inheritance starts from entity D being parent, G and F extends D. I need to fetch all entities either by EnityGraph or Join fetch. All associations are lazy. I have id of the root A. I need to fetch complete data without n+1 queries for A (aId) when I call ... aRepository.findById(aId);

I tried many solutions but i am unable to fetch. The problem to create EntityGraph is the inheritance in between entities chain. The only way i was able to fetch was when I made associations EAGER. I don't want to make @OneToMany mappings as EAGER.

Can anyone suggest me a solution (either @EntityGraph or Join Fetch) to perform this task ?

Does this answer your question? JPA inheritance @EntityGraph include optional associations of subclasses — Christian Beikov

Christian Beikov Christian Beikov · Accepted Answer · 2020-07-22T06:17:17

this seems very similar to this question here: https://stackoverflow.com/a/61272573/412446

I think you can deduce that entity graphs can't be used for this. You could use join fetch though if you want, but I think Spring Data JPA repositories can only work with entity graphs. You can still use Blaze-Persistence Entity-Views though :)

EntityGraph or Join Fetch with Inheritance in JPA/Hibernate

1 Answers