[release/7.0] Fix to #28881 - Consider removing unnecessary CASTs around JSON_VALUE #30442
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approved these changes
Mar 9, 2023
src/EFCore.SqlServer/Query/Internal/SqlServerQuerySqlGenerator.cs
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…und JSON_VALUE We can remove cast for string scalars, other types maybe cause conversion issues in the generated sql. Fixes #28881
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Ported from #29417
Fixes #28881
Description
JSON queries returning single string properties were adding unnecessary CAST.
Customer impact
Fix improves performance and readability of affected queries. Perf impact can be significant in some cases, basically allowing for index seek instead of a scan.
How found
Found by EF Core engineers.
Regression
No. JSON support has been introduced in 7.0.
Testing
Already significant test coverage (each query test verifies SQL result), added more tests for good measure.
Risk
Minimal: Fix is very isolated, only affects specific JSON scenarios projecting varchar columns - change is to remove the cast to nvarchar(max) around columns that are already strings. Added quirk to revert to old behavior if necessary.