You have a N-to-1 relationship when an object of a class has an associated object of another class
(only one associated object) and several of this type of object can be linked to the same associated
object. From the other end of the relationship it is effectively a 1-N, but from the point of view of
the object in question, it is N-1. You can create the relationship in 2 ways depending on whether the
2 classes know about each other (bidirectional), or whether only the "N" side knows about the other
class (unidirectional). These are described below.
For this case you could have 2 classes,
, as below.
class ("N" side) knows about the
class ("1" side), but not
vice-versa. A particular user could be related to several accounts. If you define the Meta-Data
for these classes as follows
<class name="User" identity-type="datastore">
<class name="Account" identity-type="datastore">
<field name="user" persistence-modifier="persistent"/>
This will create 2 tables in the database, one for
), and one
and a column
), as shown below.
Things to note :-
If you wish to specify the names of the database tables and columns for these classes, you can
use the attribute
element) and the attribute
If you call
on the end of a 1-1 unidirectional relation without the
relation and that object is related to another object, an exception will typically be thrown
(assuming the RDBMS supports foreign keys). To delete this record you should remove the other
objects association first.
This relationship is described in the guide for 1-N
relationships. In particular there are 2 ways to define the relationship. The
first uses a Join Table to hold the relationship.
The second uses a Foreign Key in the "N" object to
hold the relationship. Please refer to the 1-N relationships bidirectional relations since they
show this exact relationship.