Fixed #28658 -- Added DISTINCT handling to the Aggregate class.

2 files changed, 25 insertions, 1 deletions

diff --git a/docs/ref/models/expressions.txt b/docs/ref/models/expressions.txt
index 7a358a5ce8..2413952228 100644
--- a/docs/ref/models/expressions.txt
+++ b/docs/ref/models/expressions.txt
@@ -373,7 +373,7 @@ some complex computations::
 
 The ``Aggregate`` API is as follows:
 
-.. class:: Aggregate(*expressions, output_field=None, filter=None, **extra)
+.. class:: Aggregate(*expressions, output_field=None, distinct=False, filter=None, **extra)
 
     .. attribute:: template
 
@@ -392,6 +392,14 @@ The ``Aggregate`` API is as follows:
         Defaults to ``True`` since most aggregate functions can be used as the
         source expression in :class:`~django.db.models.expressions.Window`.
 
+    .. attribute:: allow_distinct
+
+        .. versionadded:: 2.2
+
+        A class attribute determining whether or not this aggregate function
+        allows passing a ``distinct`` keyword argument. If set to ``False``
+        (default), ``TypeError`` is raised if ``distinct=True`` is passed.
+
 The ``expressions`` positional arguments can include expressions or the names
 of model fields. They will be converted to a string and used as the
 ``expressions`` placeholder within the ``template``.
@@ -409,6 +417,11 @@ should define the desired ``output_field``. For example, adding an
 ``IntegerField()`` and a ``FloatField()`` together should probably have
 ``output_field=FloatField()`` defined.
 
+The ``distinct`` argument determines whether or not the aggregate function
+should be invoked for each distinct value of ``expressions`` (or set of
+values, for multiple ``expressions``). The argument is only supported on
+aggregates that have :attr:`~Aggregate.allow_distinct` set to ``True``.
+
 The ``filter`` argument takes a :class:`Q object <django.db.models.Q>` that's
 used to filter the rows that are aggregated. See :ref:`conditional-aggregation`
 and :ref:`filtering-on-annotations` for example usage.
@@ -416,6 +429,10 @@ and :ref:`filtering-on-annotations` for example usage.
 The ``**extra`` kwargs are ``key=value`` pairs that can be interpolated
 into the ``template`` attribute.
 
+.. versionadded:: 2.2
+
+    The ``allow_distinct`` attribute and ``distinct`` argument were added.
+
 Creating your own Aggregate Functions
 -------------------------------------
 
diff --git a/docs/releases/2.2.txt b/docs/releases/2.2.txt
index c8515d5ba6..150fe413db 100644
--- a/docs/releases/2.2.txt
+++ b/docs/releases/2.2.txt
@@ -239,6 +239,13 @@ Models
 * Added SQLite support for the :class:`~django.db.models.StdDev` and
   :class:`~django.db.models.Variance` functions.
 
+* The handling of ``DISTINCT`` aggregation is added to the
+  :class:`~django.db.models.Aggregate` class. Adding :attr:`allow_distinct =
+  True <django.db.models.Aggregate.allow_distinct>` as a class attribute on
+  ``Aggregate`` subclasses allows a ``distinct`` keyword argument to be
+  specified on initialization to ensure that the aggregate function is only
+  called for each distinct value of ``expressions``.
+
 Requests and Responses
 ~~~~~~~~~~~~~~~~~~~~~~