CODEWITHSUNDEEP
javahibernatejpahibernate-annotations
Reza P.
Reza P.

Reputation: 306

JPA using one join table for two OneToMany entity

There's an Entity Class 'A' (supposed to be a Person),There's another Entity Class 'B' (supposed to be a Contract).

Entity 'A' has a relation @OneToMany to Class 'B' ( a person can sign alot of contracts). Entity 'B' also has a relation @OneToMany to Class 'A' (a contract can have many person signing it).

In this case, there's gonna be 2 JoinTable in database, but actually they both are somehow the same.

Is there anyway that i make them just using One JoinTable?

tnx for any help!

Upvotes: 2

Views: 2185

Answers (4)

cнŝdk
cнŝdk

Reputation: 32165

Situation:

You are complicating things here, the appropriate relationship between your Entities would be ManyToMany, because :

  • A person can sign many contracts.
  • And a contract can be signed by many persons.

And one JoinTable in this relationship is sufficient to give you all the requested details:

  • Who signed a given Contract.
  • Which Contracts have a Person signed.

Mapping:

So your mapping will be like this:

In your Person class:

@ManyToMany(mappedBy = "persons")
private Set<Contract> contracts= new HashSet<Contract>();

And in your Contract class:

@ManyToMany(cascade = CascadeType.ALL)
@JoinTable(
        name = "PERSONS_CONTRACTS",
        joinColumns = @JoinColumn(name = "CONTRACT_ID"),
        inverseJoinColumns = @JoinColumn(name = "PERSON_ID")
)
private Set<Person> persons= new HashSet<Person>();

You can check this Hibernate Many-to-Many Association Annotations Example for further details.

Upvotes: 1

Afridi
Afridi

Reputation: 6922

Its a kind of Many to Many relationships. So it need just one junction table like person_contract in database. It will contains columns like:

  1. Person_id
  2. Contract_id

where both person_id & contract_id will be a composite unique key.

In hibernate it will be: 1. In Person table

@ManyToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
@JoinTable(name = "person_contract ", joinColumns = {
        @JoinColumn(name = "person_id", nullable = false, updatable = false) },
        inverseJoinColumns = { @JoinColumn(name = "contract_id",
                nullable = false, updatable = false) })
public Set<Contract> contracts;

  1. In Contract table

    @ManyToMany(fetch = FetchType.LAZY, mappedBy = "contracts") public Set<Person> persons;

Upvotes: 1

Fortega
Fortega

Reputation: 19702

Looks like a @ManyToMany relation to me...

in class Person

@ManyToMany
@JoinTable(name="PERS_CONTRACTS")
public Set<Contract> getContracts() { return contracts; }

in class Contract

@ManyToMany(mappedBy="contracts")
public Set<Person> getSigners() { return signers; }

Upvotes: 2

Azzabi Haythem
Azzabi Haythem

Reputation: 2423

By using two @OneToMany there is no JoinTable. you can use @ManyToMany like this

@ManyToMany
  @JoinTable(
      name="AB",
      joinColumns=@JoinColumn(name="A_ID", referencedColumnName="ID"),
      inverseJoinColumns=@JoinColumn(name="B_ID", referencedColumnName="ID"))
  private List<B> bS;

Upvotes: 1

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