Remove from one side of the many to many in Nhibernate

Question

Hi there,

I have these 2 objects in NHibernate forming a many to many relationship:

User:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
                   assembly="Providers" namespace="Providers.Objects">

  <class name="User" table="Users">

    <id name="UserId" type="int">
      <generator class="native" />
    </id>

    <many-to-one name="Application" column="ApplicationId" cascade="none" />    

    <property name="UserName" type="string" />
    <property name="LoweredUserName" type="string" />
    <property name="MobileAlias" type="string" />
    <property name="IsAnonymous" type="bool" />
    <property name="LastActivityDate" type="DateTime" />

    <bag name="Roles" table="UsersInRoles" lazy="true" cascade="none" >
      <key column="UserId"></key>
      <many-to-many class="Role" column="RoleId"></many-to-many>
    </bag>

  </class>

</hibernate-mapping>

And Role:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
                   assembly="Providers" namespace="Providers.Objects">

  <class name="Role" table="Roles">

    <id name="RoleId" type="int">
      <generator class="native" />
    </id>

    <many-to-one name="Application" column="ApplicationId" class="Application" cascade="none" />    

    <property name="RoleName" type="string" />
    <property name="LoweredRoleName" type="string" />
    <property name="Description" type="string" />

    <bag name="Users" table="UsersInRoles" lazy="true" inverse="true" cascade="none" >
      <key column="RoleId"></key>
      <many-to-many class="User" column="UserId"></many-to-many>
    </bag>

  </class>

</hibernate-mapping>

Let's say the role backupoperator has some users in it. If I try to remove one of the users from the role instance, like:

var backupoperator = GetRoleByName(session, app.ApplicationId, "backupoperator");
backupoperator.Users.RemoveAt(0);
session.Update(backupoperator);
transaction.Commit();

It doesn't work :( The association remains unchanged in the database. When I try the opposite (remove a role from a user object and updating the user object), it works. Is it because of the inverse attribute in the NHibernate mapping?

How to accomplish what I am trying to do? (remove a user from a role, updating the role and having that persisted)?

Thanks

Answer 1

When you write inverse="true" you are telling NHibernate that the other side maintains the relationship.

Therefore, you have to remove the Role from the User's Roles collection if you want your change persisted.