Question

I have an entity User and it should have property manager where manager is another user (one manager can manage many users, any user may have only 1 manager or have not any).

How can I implement this?

I tried something standard

@ManyToOne
@JoinColumn (name = ??? /* what should be here? */, nullable = true)
private User manager;

but it’s not as simple as it seems..

Answer 1

What’s the problem? Use the default value i.e. don’t set the name if you don’t know how to name the join column (should default to something like MANAGER_ID). From the javadoc of the name attribute:

(Optional) The name of the foreign key
column. The table in which it is found
depends upon the context. If the join
is for a OneToOne or Many- ToOne
mapping, the foreign key column is in
the table of the source entity. If the
join is for a ManyToMany, the foreign
key is in a join table. Default (only
applies if a single join column is
used): The concatenation of the
following: the name of the referencing
relationship property or field of the
referencing entity; “_”; the name of
the referenced primary key column. If
there is no such referencing
relationship property or field in the
entity, the join column name is formed
as the concatenation of the following:
the name of the entity; “_”; the name
of the referenced primary key column.