Many-to-many relationship with columns in the association in propel - database

Question

I want to have in generated by Propel objects function e.g. getUsersPrivileges(). I have two tables Users and Privileges described as;
<table name="users" phpName="User">
<column name="user_id" type="integer" required="true" autoIncrement="true" primaryKey="true" />
<column name="login" type="longvarchar" required="true" />
<column name="password" type="longvarchar" required="true" />
<column name="email" type="longvarchar" required="true" />
<column name="language" type="longvarchar" required="true" defaultValue="en" />
<column name="salt1" type="longvarchar" required="true" />
<column name="salt2" type="longvarchar" required="true" />
<column name="date_created" type="timestamp" required="true" />
<column name="archived" type="integer" required="true" defaultValue="0" />
</table>
<table name="privileges" phpName="Privilege">
<column name="privilege_id" type="integer" required="true" autoIncrement="true" primaryKey="true" />
<column name="name" type="longvarchar" required="true" />
<column name="description" type="longvarchar" required="true" />
</table>
<table name="users_privileges" phpName="UserPrivilege" isCrossRef="true">
<column name="user_privilege_id" type="integer" required="true" autoIncrement="true" unique="true" primaryKey="true" />
<column name="user_id" type="integer" />
<column name="privilege_id" type="integer" />
<column name="archived" type="integer" required="true" defaultValue="0" />
<foreign-key foreignTable="users">
<reference local="user_id" foreign="user_id"/>
</foreign-key>
<foreign-key foreignTable="privileges">
<reference local="privilege_id" foreign="privilege_id"/>
</foreign-key>
</table>
I want to have a user_privilege_id as primary key in SQL schema, but Propel requires to generated this method that columns user_id and privilege_id as primary key and foreign key to users.user_id and privilege_id to privileges.privilege_id. It is good to have any additional column in this table.
How to tell Propel to join these tables through these columns and no primary key?

Answer 1

It doesn't work. PrimaryKeys are the only way Propel knows which relations from left to right should created. If you add additional PKs it will create different relation methods. If you have a completely different PK Propel is unable to check which outgoing relations from the cross-table needs to be cross linked from user to privileges and vice-versa. If you really need a ID, you can add this id column as normal with a unique constrain and auto-increment.
Or alternative, you don't use isCrossRef and write your relation methods from user to privileges and vice-versa on your own.