Hibernate no default value found having multiple manytomany mappings to the same entities

Question

User has these :

@ManyToMany(mappedBy = "votedDownBy")
private Set<Foo> votedDown =new HashSet<Foo>();

@ManyToMany(mappedBy = "favouritedBy")
private Set<Foo> favourites = new HashSet<Foo>();

The corresponding Foo has these :

@ManyToMany
private Set<User> votedDownBy = new HashSet<User>();

@ManyToMany
private Set<User> favouritedBy = new HashSet<User>();

When deploying I am getting no default value provided for votedDownBy_id ... and I don't know why ?

Answer 1

@ManyToMany mappings are done using join tables. In your case, there must be a Foo_User table that has these mappings. ie, a Foo_id and a User_id column. (Substitute Foo_id and User_id with the respective primary keys. Also substitute Foo_User with Table1_Table2 where Table1 is the table for Foo and Table2 for User )

You can override these defaults using the @JoinTable annotation:

@ManyToMany(mappedBy = "votedDownBy")
@JoinTable(name="User_Foo_Votedown", 
            joinColumns={@JoinColumn(name="User_ID")}, 
            inverseJoinColumns={@JoinColumn(name="Foo_id")})
private Set<Foo> votedDown =new HashSet<Foo>();

@ManyToMany(mappedBy = "favouritedBy")
@JoinTable(name="User_Foo_Fav", 
            joinColumns={@JoinColumn(name="User_ID")}, 
            inverseJoinColumns={@JoinColumn(name="Foo_id")})
private Set<Foo> favourites = new HashSet<Foo>();

and

@ManyToMany(mappedBy = "votedDown")
private Set<User> votedDownBy = new HashSet<User>();

@ManyToMany(mappedBy = "favorites")
private Set<User> favouritedBy = new HashSet<User>();

You can also put the mappedBy annotation in User and the JoinTable in Foo since this is a symmetric bidirectional relationship.

Answer 2

Just adding join table to each mapping fixed it, foo class now looks like this :

@ManyToMany
@JoinTable(name="user_foo_vote_down")
private Set<User> votedDownBy = new HashSet<User>();

@ManyToMany
@JoinTable(name="user_foo_favourite")
private Set<User> favouritedBy = new HashSet<User>();