.NET 6 LINQ DistinctBy not supported exception-CodePudding

In my .NET 6,0 app I'm trying to use (new to .NET 6.0 https://learn.microsoft.com/en-us/dotnet/api/system.linq.queryable.distinctby?view=net-6.0) method DistinctBy, something like this:

return context.Table
    .Where(x => x.IsLive)
    .DistinctBy(x => x.Field1)
    .ToList();

Buld is fine, no errors, but at runtime I get this:

Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware[1]
  An unhandled exception has occurred while executing the request.
  System.NotSupportedException: LINQ to Entities does not recognize the method 'System.Linq.IQueryable`1[MyType] DistinctBy[DbFundHistoPrice,String](System.Linq.IQueryable`1[VanEck.Repositories.Entities.Website.Funds.DbFundHistoPrice], System.Linq.Expressions.Expression`1[System.Func`2[VanEck.Repositories.Entities.Website.Funds.DbFundHistoPrice,System.String]])' method, and this method cannot be translated into a store expression.
     at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.DefaultTranslator.Translate(ExpressionConverter parent, MethodCallExpression call)
     at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.MethodCallTranslator.TypedTranslate(ExpressionConverter parent, MethodCallExpression linq)
     at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.TranslateExpression(Expression linq)
     at System.Data.Entity.Core.Objects.ELinq.ExpressionConverter.Convert()
     at System.Data.Entity.Core.Objects.ELinq.ELinqQueryState.GetExecutionPlan(Nullable`1 forMergeOption)
     at System.Data.Entity.Core.Objects.ObjectQuery`1.<>c__DisplayClass41_0.<GetResults>b__1()
     at System.Data.Entity.Core.Objects.ObjectContext.ExecuteInTransaction[T](Func`1 func, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction, Boolean releaseConnectionOnSuccess)
     at System.Data.Entity.Core.Objects.ObjectQuery`1.<>c__DisplayClass41_0.<GetResults>b__0()
     at System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute[TResult](Func`1 operation)
     at System.Data.Entity.Core.Objects.ObjectQuery`1.<System.Collections.Generic.IEnumerable<T>.GetEnumerator>b__31_0()
     at System.Data.Entity.Internal.LazyEnumerator`1.MoveNext()
     at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
     at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
     *my call here*

Other queries without new .NET 6 methods work fine (upgrading from 5 so there are some).

What am I missing here? Somethig in startup or in project settings?

I know that these extensions can be trimmed during build but I see no reason for that here since the method is actually used.

CodePudding user response：

It seems you are using older ORM (EF 6?) which does not support this method.

DistinctBy is not supported even by EF Core (which I recommend upgrading to) at the moment. See this issue - Translate LINQ DistinctBy. You can try rewriting it with GroupBy(e => e.Field1).Select(g => g.First()).