Commit 28756577 authored by Ramiro Morales's avatar Ramiro Morales
Browse files

Added support for modifying the effect of ``DISTINCT`` clauses so they 

only consider some fields (PostgreSQL only).

For this, the ``distinct()`` QuerySet method now accepts an optional
list of model fields names and generates ``DISTINCT ON`` clauses on
these cases. Thanks Jeffrey Gelens and Anssi Kääriäinen for their work.

Fixes #6422.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@17244 bcc190cf-cafb-0310-a4f2-bffc1f526a37
parent 03eb2907

AUTHORS

+2 −0
Original line number Diff line number Diff line
@@ -203,6 +203,7 @@ answer newbie questions, and generally made Django that much better: 
    Marc Garcia <marc.garcia@accopensys.com>

    Andy Gayton <andy-django@thecablelounge.com>

    geber@datacollect.com

    Jeffrey Gelens <jeffrey@gelens.org>

    Baishampayan Ghose

    Joshua Ginsberg <jag@flowtheory.net>

    Dimitris Glezos <dimitris@glezos.com>
@@ -269,6 +270,7 @@ answer newbie questions, and generally made Django that much better: 
    jpellerin@gmail.com

    junzhang.jn@gmail.com

    Xia Kai <http://blog.xiaket.org/>

    Anssi Kääriäinen

    Antti Kaihola <http://djangopeople.net/akaihola/>

    Peter van Kampen

    Bahadır Kandemir <bahadir@pardus.org.tr>

django/db/backends/__init__.py

+14 −0
Original line number Diff line number Diff line
@@ -406,6 +406,9 @@ class BaseDatabaseFeatures(object): 
    supports_stddev = None

    can_introspect_foreign_keys = None



    # Support for the DISTINCT ON clause

    can_distinct_on_fields = False



    def __init__(self, connection):

        self.connection = connection
@@ -559,6 +562,17 @@ class BaseDatabaseOperations(object): 
        """

        raise NotImplementedError('Full-text search is not implemented for this database backend')



    def distinct_sql(self, fields):

        """

        Returns an SQL DISTINCT clause which removes duplicate rows from the

        result set. If any fields are given, only the given fields are being

        checked for duplicates.

        """

        if fields:

            raise NotImplementedError('DISTINCT ON fields is not supported by this database backend')

        else:

            return 'DISTINCT'



    def last_executed_query(self, cursor, sql, params):

        """

        Returns a string of the query last executed by the given cursor, with

django/db/backends/postgresql_psycopg2/base.py

+1 −0
Original line number Diff line number Diff line
@@ -82,6 +82,7 @@ class DatabaseFeatures(BaseDatabaseFeatures): 
    has_select_for_update_nowait = True

    has_bulk_insert = True

    supports_tablespaces = True

    can_distinct_on_fields = True



class DatabaseWrapper(BaseDatabaseWrapper):

    vendor = 'postgresql'

django/db/backends/postgresql_psycopg2/operations.py

+6 −0
Original line number Diff line number Diff line
@@ -179,6 +179,12 @@ class DatabaseOperations(BaseDatabaseOperations): 


        return 63



    def distinct_sql(self, fields):

        if fields:

            return 'DISTINCT ON (%s)' % ', '.join(fields)

        else:

            return 'DISTINCT'



    def last_executed_query(self, cursor, sql, params):

        # http://initd.org/psycopg/docs/cursor.html#cursor.query

        # The query attribute is a Psycopg extension to the DB API 2.0.

django/db/models/query.py

+7 −3
Original line number Diff line number Diff line
@@ -323,6 +323,8 @@ class QuerySet(object): 
        If args is present the expression is passed as a kwarg using

        the Aggregate object's default alias.

        """

        if self.query.distinct_fields:

            raise NotImplementedError("aggregate() + distinct(fields) not implemented.")

        for arg in args:

            kwargs[arg.default_alias] = arg
@@ -751,12 +753,14 @@ class QuerySet(object): 
        obj.query.add_ordering(*field_names)

        return obj



    def distinct(self, true_or_false=True):

    def distinct(self, *field_names):

        """

        Returns a new QuerySet instance that will select only distinct results.

        """

        assert self.query.can_filter(), \

                "Cannot create distinct fields once a slice has been taken."

        obj = self._clone()

        obj.query.distinct = true_or_false

        obj.query.add_distinct_fields(*field_names)

        return obj



    def extra(self, select=None, where=None, params=None, tables=None,
@@ -1179,7 +1183,7 @@ class EmptyQuerySet(QuerySet): 
        """

        return self



    def distinct(self, true_or_false=True):

    def distinct(self, fields=None):

        """

        Always returns EmptyQuerySet.

        """