The primary key of the user_node table is actually just node_id. That means the database would allow the same node ID to be assigned to multiple user IDs, which is obviously not desired.

Also, currently it is impossible to define a foreign key constraint on the solaruser.user_node table's combination of (user_id, node_id), because that is not a unique constraint on the table. This would be helpful to do, because it would allow easy enforcement of (user,node) combinations.

Add a unique constraint on (user_id, node_id) to solve these issues.