JPA/Hibernate ManyToMany not nullable contstraint

Question

I have a parent entity that has a Many-to-Many relation with its children. However I have a constraint that a Parent must at least have 1 Child. How can we describe this with JPA/Hibernate annotations?

@Entity
public class Parent {
    //parent must have at least 1 Child
    @ManyToMany
    private Set<Child> children    
}

At the moment I'm thinking of just using interceptors as follows:

@PrePersist
@PreUpdate
private validate() {
    if(children.size() < 1) 
      throw new PersistenceException()
}

Or possibly handle this at service layer.

Answer 1

Try using the Hibernate Validator, that uses JSR 303 and is interpreted as database validation also. Therefore you can use the @NotEmpty annotation for validation like this:

 @ManyToMany
 @NotEmpty
    private Set<Child> children