[release/7.0] Fix to #30575 - Multiple LeftJoins (GroupJoins) lead to GroupJoin Exception when the same where is used twice - #30794
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…eption when the same where is used twice Problem is in QueryableMethodNormalizingExpressionVisitor and specifically part where we convert from GroupJoin-SelectMany-DefaultIfEmpty into left join (SelectManyVerifyingExpressionVisitor). We check if the collection selector is correlated, and we do that by looking at parameters in that lambda. Problem is that the affected queries reference outside variable that gets parameterized and that breaks the correlation finding logic. Fix is to add a step that scans entire query and identifies external parameters before we try to normalize GJSMDIE into LeftJoins, so that those external parameters are not counted as correlated. Fixes #30575
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Apr 29, 2023
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Ported from #30594
Fixes #30575
Description
Query with more multiple GroupJoin-SelectMany-DefaultIfEmpty (i.e. LEFT JOIN pattern), which use a variable, produces incorrect query.
Customer impact
Query with more multiple GroupJoin-SelectMany-DefaultIfEmpty (i.e. LEFT JOIN pattern), which use a variable, produces incorrect query. Workaround is to not use variable (i.e. constant) which is easy, when possible, but often not realistic.
How found
Customer report on 7.0.
Regression
No.
Testing
Added regression tests.
Risk
Minimal; Fix is very simple (1 line change) - an improved way to identify lambda arguments vs user variables (by looking at the name prefix). We use this strategy in other places in the code base already, so the approach has been thoroughly tested. As always, added quirk just in case.