#32663: Remove Error raising on annotation & distinct call
-------------------------------------+-------------------------------------
Reporter: Yovel | Owner: nobody
Cohen |
Type: | Status: new
Cleanup/optimization |
Component: Database | Version: 3.2
layer (models, ORM) | Keywords: SQLCompiler ORM
Severity: Normal | Query
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
-------------------------------------+-------------------------------------
if you try to call distinct on an annotated query, it sometimes works,
sometimes get's ignore, and sometimes raises an error.
I had a query facing all three scenarios and solving the last one was the
one that worked out.
the error being raised is:
```
NotImplementedError: annotate() + distinct(fields) is not implemented.
```
after looking at the source code for the exception at
django.db.models.sql.compiler.SQLCompiler
row 594
```
if grouping:
if distinct_fields:
raise NotImplementedError('annotate() + distinct(fields) is not
implemented.')
order_by = order_by or self.connection.ops.force_no_ordering()
result.append('GROUP BY %s' % ', '.join(grouping))
# rest of the as_sql() method
```
after just removing the distinct_fields condition:
```
if grouping:
order_by = order_by or self.connection.ops.force_no_ordering()
result.append('GROUP BY %s' % ', '.join(grouping))
# rest of the as_sql() method
```
it works, at least in the following ways I tried (annotations are just
made up for sake of the example)
```
model_scores_latest_date_annotation = Max('model_scores__date')
latest_score_annotation = Case(When(model_scores__date=F('latest_date'),
then='model_scores__score')
base_query_set =
(Model.objects.filter(**filters).alias(latest_date=model_scores_latest_date_annotation).values(ID).annotate(latest_score=latest_score_annotation,
latest_date=model_scores_latest_date_annotation)
```
adding the following distinct calls all worked:
```
query_set = base_query_set.order_by('latest_date').distinct('id',
'latest_date')
query_set = base_query_set.distinct('id')
query_set = base_query_set.distinct('id', 'latest_date')
```
which makes me think that the as_sql method on SQLCompiler can handle more
cases easily and this just fell beneath the cracks.
--
Ticket URL: <https://code.djangoproject.com/ticket/32663>
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