Translate ToString() over enums by Danevandy99 · Pull Request #33706 · dotnet/efcore

Danevandy99 · 2024-05-13T11:56:07Z

Fixes #33635 and #20604

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Danevandy99 · 2024-05-16T00:57:42Z

@roji @cincuranet This is ready to review again.

roji

In addition to the below comments, one more general note...

Translations where we duplicate an expression multiple times are problematic, since the expression may be arbitrarily complex. For example, if instance here is a complex subquery, that subquery would get evaluated by the database N times (once for each CASE); this is bad enough for perf that we refrain from translating in most such cases (e.g. entity equality).

At least for now, we should do the same here, i.e. perform the CASE/WHEN translation only when instance is a column or a parameter - can you please add that check?

roji · 2024-05-16T07:49:43Z

+                && converter.GetType().IsGenericType
+                && converter.GetType().GetGenericTypeDefinition() == typeof(EnumToStringConverter<>))
+            {
+                return _sqlExpressionFactory.MakeUnary(ExpressionType.Convert, instance, typeof(string));


Since the enum is already mapped to a string in the database, an actual SQL cast shouldn't be necessary here. However, there's still a CLR type change here, and we currently lack the ability to "change" the CLR type without a corresponding SQL expression node.

Can you please leave a TODO comment here, referencing #33733?

Yep! I did attempt to just return the instance without the cast at one point, but ran into issues that seemed larger than the scope of this issue.

roji · 2024-05-16T07:59:53Z

            && @object!.Type.IsNullableType()
-            && methodCallExpression.Method.Name != nameof(Nullable<int>.GetValueOrDefault))
+            && methodCallExpression.Method.Name != nameof(Nullable<int>.GetValueOrDefault)
+            && methodCallExpression.Method.Name != nameof(Nullable<int>.ToString))


Can you explain why this change is needed?

Calling ToString on a nullable value type like an enum returns an empty string if the value is null, rather than null: https://learn.microsoft.com/en-us/dotnet/api/system.nullable-1.tostring?view=net-8.0 Without that check, the in-memory query returns null if the value of the nullable enum is null, rather than an empty string like C# usually does.

Looks like that might also allow ToString to be called on a reference type, since @object!.Type.IsNullableType() returns true for non-value types and we're only comparing the method names. The new check should probably include @object!.Type.IsNullableValueType()

See my new review comment about not returning an empty string as the default case, but rather a string representation of the integer enum value (which is what .NET does). If we do that, then the NULL should simply bubble out through the conversion, which I think is the behavior we want, right? If so, then this change shouldn't be necessary.

Yes, the change you mentioned in your other comment seems like it should make this change unnecessary. I'll remove it and let you know if that doesn't end up working.

roji · 2024-06-03T05:14:36Z

            && @object!.Type.IsNullableType()
-            && methodCallExpression.Method.Name != nameof(Nullable<int>.GetValueOrDefault))
+            && methodCallExpression.Method.Name != nameof(Nullable<int>.GetValueOrDefault)
+            && methodCallExpression.Method.Name != nameof(Nullable<int>.ToString))


See my new review comment about not returning an empty string as the default case, but rather a string representation of the integer enum value (which is what .NET does). If we do that, then the NULL should simply bubble out through the conversion, which I think is the behavior we want, right? If so, then this change shouldn't be necessary.

roji

Thanks, this is starting to get close. I'll be available in the coming time to push this to completion (I was traveling quite a lot in recent weeks).

Fixes dotnet#33635 and dotnet#20604

Danevandy99 · 2024-06-04T02:00:56Z

@roji GitHub wasn't letting me reply to this comment (#33706 (comment)), but the behavior we want is for the result to be an empty string if we call ToString on a nullable enum, since that's what C# does (https://learn.microsoft.com/en-us/dotnet/api/system.nullable-1.tostring?view=net-8.0). I tested it, and that change is still necessary, otherwise the code inside that if block bypasses the ToString call and just returns null instead of the empty string.

roji

Good catch with the empty-string returning behavior of Nullable.ToString().

This is almost done - see some final comments. There are also some test failures.

roji · 2024-06-04T05:37:30Z

+        AssertSql(
+"""
+SELECT CASE
+    WHEN "g"."Rank" = 0 THEN 'None'


This still needs to be updated (causes test failures)

roji

Thanks for the quick turnaround and for the patience! LGTM.

Danevandy99 · 2024-06-04T18:59:53Z

@roji Of course! Thanks for all your guidance. Is there anything I need to do for this to get it into a release build (I'm assuming it'll be in one of the .NET 9 previews)?

roji · 2024-06-04T19:07:40Z

Nope, it's merged and will appear in a coming preview!

Danevandy99 · 2024-06-05T11:37:03Z

Awesome, thanks!

Danevandy99 mentioned this pull request May 13, 2024

Fixes #20604 - Treat ToString as casting to string in the database #33701

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roji mentioned this pull request May 14, 2024

Treat ToString as casting to string in the database #20604

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Danevandy99 changed the title ~~Fixes #33635 - Translate ToString on enums with number store types as a CASE/WHEN expression~~ Fixes #33635 and #20604 May 16, 2024

roji changed the title ~~Fixes #33635 and #20604~~ Translate ToString() over enums May 16, 2024

roji requested changes May 16, 2024

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Danevandy99 requested a review from roji May 18, 2024 20:51

Danevandy99 force-pushed the translate-to-string-on-enums-with-number-store-types-to-case-expression branch from 475fd88 to 5333cd5 Compare May 27, 2024 21:52

Danevandy99 requested review from AndriySvyryd and maumar as code owners May 27, 2024 21:52

Danevandy99 changed the base branch from release/8.0 to main May 27, 2024 21:53

Danevandy99 force-pushed the translate-to-string-on-enums-with-number-store-types-to-case-expression branch from 9f353a0 to 56841ce Compare May 27, 2024 22:57

AndriySvyryd assigned roji May 29, 2024

roji reviewed Jun 3, 2024

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roji requested changes Jun 3, 2024

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ranma42 mentioned this pull request Jun 3, 2024

Fix optimization of CASE op WHEN #33869

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Danevandy99 added 2 commits June 3, 2024 18:39

Translate ToString() over enums

55762db

Fixes dotnet#33635 and dotnet#20604

Requested changes WIP

126c618

Danevandy99 force-pushed the translate-to-string-on-enums-with-number-store-types-to-case-expression branch from 7efbfdf to 126c618 Compare June 3, 2024 23:39

roji requested changes Jun 4, 2024

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Danevandy99 added 2 commits June 4, 2024 09:13

Fixing tests, making requested changes

3dfe409

Formatting fix

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roji approved these changes Jun 4, 2024

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roji merged commit 80e9dce into dotnet:main Jun 4, 2024

ajcvickers added the community-contribution label Jun 5, 2024

roji mentioned this pull request Sep 23, 2024

[9.0] New translations and SQL optimization/simplification #34151

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maumar mentioned this pull request Mar 5, 2025

EF Core InMemory database throws an argument exception on Nullable<>.ToString #35299

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Danevandy99 commented May 13, 2024 •

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