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Add support for filter expression in GroupConcat #948

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Add support for filter expression in GroupConcat #948

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537d035
Add support for filter expression in GroupConcat
caramdache Sep 14, 2022
452d3c8
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Sep 14, 2022
24c0e35
Update src/django_mysql/models/aggregates.py
caramdache Sep 14, 2022
97ea273
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Sep 14, 2022
65b301c
Add missing name and allow_distinct variables
caramdache Sep 14, 2022
b3e4a2c
Add support for ordering and separator when filter is present
caramdache Sep 14, 2022
451597b
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Sep 14, 2022
96e7c9a
Fix bug introduced in legacy path
caramdache Sep 15, 2022
8c5c5e1
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Sep 15, 2022
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12 changes: 11 additions & 1 deletion src/django_mysql/models/aggregates.py
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Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,7 @@ class GroupConcat(Aggregate):
def __init__(
self,
expression: Expression,
filter=None,
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distinct: bool = False,
separator: str | None = None,
ordering: str | None = None,
Expand All @@ -38,7 +39,7 @@ def __init__(
# This can/will be improved to SetTextField or ListTextField
extra["output_field"] = CharField()

super().__init__(expression, **extra)
super().__init__(expression, filter=filter, **extra)

self.distinct = distinct
self.separator = separator
Expand All @@ -53,6 +54,15 @@ def as_sql(
connection: BaseDatabaseWrapper,
**extra_context: Any,
) -> tuple[str, tuple[Any, ...]]:
if self.filter:
extra_context["distinct"] = "DISTINCT " if self.distinct else ""
copy = self.copy()
copy.filter = None
source_expressions = copy.get_source_expressions()
condition = When(self.filter, then=source_expressions[0])
copy.set_source_expressions([Case(condition)] + source_expressions[1:])
return super(Aggregate, copy).as_sql(compiler, connection, **extra_context)
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I haven't looked into it, but it's a bit odd that you're skipping the existing implementation and calling super(). The implemetnation below covers the SQL oddities in GROUP_CONCAT, I think we'd still want to use it, just tweak adding the filter there.

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I'm not sure we need keep the existing pathway in the long term. It's probably better to let Aggregate.as_sql() perform the work based on the template.

If you look at the code for Count, you'll see there are 2 paths, one when filter is set, the other when it's not. I think we should have a similar structure here, but avoid manual handcrafting as much as possible because this is likely fragile.


connection.ops.check_expression_support(self)
sql = ["GROUP_CONCAT("]
if self.distinct:
Expand Down