Hibernate inheritance single table

Question

I am trying to implement a single table Hibernate inheritance strategy with a DB table "persons".

I have a family which contains a husband, a wife, a list of children and a list of other inmates. Each person may be a member of many families (i.e. a husband may be a husband in one family and a child in other).

@Entity
@Table(name = "families")
public class Family extends BaseObject {
    private Parent husband;
    private Parent wife;
    private String surname;

    private List<Child> children = new ArrayList<Child>();
    private List<Other> others = new ArrayList<Other>();

    @ManyToOne(optional = true, cascade = CascadeType.ALL)
    @JoinColumn(name = "husband_id", nullable = true)
    public Parent getHusband() {
        return husband;
    }

    @ManyToOne(optional = true, cascade = CascadeType.ALL)
    @JoinColumn(name = "wife_id", nullable = true)
    public Parent getWife() {
        return wife;
    }

    @LazyCollection(LazyCollectionOption.TRUE)
    @ManyToMany(cascade=CascadeType.ALL)
    @JoinTable(name="persons_families", joinColumns=@JoinColumn(name="family_id"), inverseJoinColumns=@JoinColumn(name="person_id"))
    public List<Other> getOthers() {
        return others;
    }

    @LazyCollection(LazyCollectionOption.TRUE)
    @ManyToMany(cascade=CascadeType.ALL)
    @JoinTable(name="persons_families", joinColumns=@JoinColumn(name="family_id"), inverseJoinColumns=@JoinColumn(name="person_id"))
    public List<Child> getChildren() {
        return children;
    }

Persons is a common class for all persons:

@Entity
@Table(name = "persons")
@DiscriminatorColumn(name = "type")
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)

public class Person extends BaseObject {
    private List<Family> families;

    @ManyToMany(cascade=CascadeType.ALL)  
    @ManyToMany(cascade=CascadeType.ALL)
@JoinTable(name="persons_families", joinColumns=@JoinColumn(name="person_id"), inverseJoinColumns=@JoinColumn(name="family_id"))
    public List<Family> getFamilies() {
        return families;
    }

Child and Other and Parent classes are identical:

@Entity
@Table(name = "persons")
@DiscriminatorValue(value = "children")
public class Child extends Person {}

@Entity
@Table(name = "persons")
@DiscriminatorValue(value = "others")
public class Other extends Person {}

@Entity
@Table(name = "persons")
@DiscriminatorValue(value = "parents")
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
public class Parent extends Person {}

Now during the system startup I have the following problem:

org.hibernate.MappingException: Repeated column in mapping for entity: org.parafia.model.Other column: type (should be mapped with insert="false" update="false")

What could I do about that? Does my model make sense?

Best regards

giorgiga · Accepted Answer · 2018-02-27T20:01:33.363

1

Does my model make sense?

It does not: if your goal is that, say, Alice is a mother in some family and also a child in some other, what should the type of Alice's row in persons be? Should Alice be an instance of Parent or Child?

Subclasses must be disjunct sets.

edited Feb 27 '18 at 20:01

answered Feb 22 '18 at 10:01

giorgiga

1,758
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My fault, I understand. It seems that if I would like to have Alice as mother and a child at the same time I need a hibernate JOINED inheritance strategy. And have a table persons with some basic info about Alice and the same record in children and parents tables. Is that right? – Gandalf Feb 22 '18 at 15:04
No @Gandalf: an instance of `Child` *cannot* also be an instance of `Parent`: that's in Java too, not only in Hibernate :-) – giorgiga Feb 22 '18 at 19:21
OK :-) So it seems that I need to use one common table persons. Family is linked to some person with mother_id and to another person with father_id. Family also have a list of children and a list of other inmates. Is there a way to have a joining table for many-to-many association with additional field of the type of this association (child or other inmate)? – Gandalf Feb 24 '18 at 15:27
@Gandalf It's been a while since I last used JPA, but IIRC `@ManyToMany` only worked for "simple" (unqualified) relations. Regardless, I'd recommend making an entity out of the many-to-many table (with id and all): the id makes everything simpler and – sooner or later – you are bound to need to add more cols to the table (it *always* happens) – giorgiga Mar 01 '18 at 22:18
Do NOT use composite keys. For any reason. Ever. :) – giorgiga Mar 01 '18 at 22:19

Hibernate inheritance single table

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