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Diffstat (limited to 'docs/topics/db/aggregation.txt')
| -rw-r--r-- | docs/topics/db/aggregation.txt | 14 |
1 files changed, 10 insertions, 4 deletions
diff --git a/docs/topics/db/aggregation.txt b/docs/topics/db/aggregation.txt index 51942d9a1c..a861959e66 100644 --- a/docs/topics/db/aggregation.txt +++ b/docs/topics/db/aggregation.txt @@ -284,9 +284,6 @@ two authors with the same name, their results will be merged into a single result in the output of the query; the average will be computed as the average over the books written by both authors. -The annotation name will be added to the fields returned -as part of the ``ValuesQuerySet``. - Order of ``annotate()`` and ``values()`` clauses ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -303,12 +300,21 @@ output. For example, if we reverse the order of the ``values()`` and ``annotate()`` clause from our previous example:: - >>> Author.objects.annotate(average_rating=Avg('book__rating')).values('name') + >>> Author.objects.annotate(average_rating=Avg('book__rating')).values('name', 'average_rating') This will now yield one unique result for each author; however, only the author's name and the ``average_rating`` annotation will be returned in the output data. +You should also note that ``average_rating`` has been explicitly included +in the list of values to be returned. This is required because of the +ordering of the ``values()`` and ``annotate()`` clause. + +If the ``values()`` clause precedes the ``annotate()`` clause, any annotations +will be automatically added to the result set. However, if the ``values()`` +clause is applied after the ``annotate()`` clause, you need to explicitly +include the aggregate column. + Aggregating annotations ----------------------- |