Unique for M2M fields

managers.py

from django.db.models import QuerySet, Manager


class BaseRankManager(Manager):

    def rank(self, field_name, user_id, **kwargs):
        """
        Gets unique items from the datebase based on the foreign key. this
        queryset is ordered in reverse chronological order.
        Args:
            field_name (str): name of the foreign key field
            user_id (int): user upon which the result is to be filtered.
            **kwargs (dict): extra keyword which match column enteries if needed
        Returns:
            name (object): RawQuerySet, limited in its functionality, but can be
            iterated over.
        """
        db_name = self.model._meta.db_table
        query = """
            SELECT * FROM (
                SELECT *,
                rank() OVER (
                    PARTITION BY {field_name}_id
                    ORDER BY added_on DESC
                    ) FROM {db_name}
                ) videosrank
        """.format(field_name=field_name, db_name=db_name)

        ordering = ' ORDER BY added_on DESC;'

        where_stmnt = 'WHERE rank = 1 AND user_id = {user_id}'.format(
            user_id=user_id
        )

        if len(kwargs):
            for k, v in kwargs.iteritems():
                # v = "1" if v == True else "0"
                where_stmnt += ' AND {k} = {v}'.format(k=k, v=v)

        query += where_stmnt
        query += ordering

        return self.raw(query)