Aggregate function distinct count throw InvalidOperationException

[voronov-maxim]

I try implement OData countdistinct. In Ef core 2.2.6 this code worked without exception.

Exception message: Processing of the LINQ expression 'AsQueryable<IGrouping<int, Order>>(GroupBy<Order, int>(
    source: NavigationTreeExpression
        Value: default(IGrouping<string, Order>)
        Expression: (Unhandled parameter: e), 
    keySelector: (o) => o.Id))' by 'NavigationExpandingExpressionVisitor' failed. This may indicate either a bug or a limitation in EF Core. See https://go.microsoft.com/fwlink/?linkid=2101433 for more detailed information.

Stack trace:
   at Microsoft.EntityFrameworkCore.Query.Internal.NavigationExpandingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression)
   at System.Linq.Expressions.MethodCallExpression.Accept(ExpressionVisitor visitor)
   at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
   at Microsoft.EntityFrameworkCore.Query.Internal.NavigationExpandingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression)
   at System.Linq.Expressions.MethodCallExpression.Accept(ExpressionVisitor visitor)
   at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
   at System.Dynamic.Utils.ExpressionVisitorUtils.VisitArguments(ExpressionVisitor visitor, IArgumentProvider nodes)
   at System.Linq.Expressions.ExpressionVisitor.VisitNew(NewExpression node)
   at System.Linq.Expressions.NewExpression.Accept(ExpressionVisitor visitor)
   at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
   at Microsoft.EntityFrameworkCore.Query.Internal.NavigationExpandingExpressionVisitor.ExpandNavigationsInExpression(NavigationExpansionExpression source, Expression expression)
   at Microsoft.EntityFrameworkCore.Query.Internal.NavigationExpandingExpressionVisitor.ExpandNavigationsInLambdaExpression(NavigationExpansionExpression source, LambdaExpression lambdaExpression)
   at Microsoft.EntityFrameworkCore.Query.Internal.NavigationExpandingExpressionVisitor.ProcessSelect(NavigationExpansionExpression source, LambdaExpression selector)
   at Microsoft.EntityFrameworkCore.Query.Internal.NavigationExpandingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression)
   at System.Linq.Expressions.MethodCallExpression.Accept(ExpressionVisitor visitor)
   at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
   at Microsoft.EntityFrameworkCore.Query.Internal.NavigationExpandingExpressionVisitor.ExpandAndReduce(Expression query, Boolean applyInclude)
   at Microsoft.EntityFrameworkCore.Query.Internal.NavigationExpandingExpressionVisitor.Expand(Expression query)
   at Microsoft.EntityFrameworkCore.Query.QueryTranslationPreprocessor.Process(Expression query)
   at Microsoft.EntityFrameworkCore.Query.QueryCompilationContext.CreateQueryExecutor[TResult](Expression query)
   at Microsoft.EntityFrameworkCore.Storage.Database.CompileQuery[TResult](Expression query, Boolean async)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.CompileQueryCore[TResult](IDatabase database, Expression query, IModel model, Boolean async)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.<>c__DisplayClass9_0`1.<Execute>b__0()
   at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQueryCore[TFunc](Object cacheKey, Func`1 compiler)
   at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQuery[TResult](Object cacheKey, Func`1 compiler)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.Execute[TResult](Expression query)
   at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryProvider.Execute[TResult](Expression expression)
   at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable`1.GetEnumerator()
   at System.Collections.Generic.LargeArrayBuilder`1.AddRange(IEnumerable`1 items)
   at System.Collections.Generic.EnumerableHelpers.ToArray[T](IEnumerable`1 source)
   at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
   at OdataToEntity.Test.EfCore.SqlServer.Program.<Main>d__0.MoveNext() in E:\vorona\OdataToEntity\test\OdataToEntity.Test.EfCore.SqlServer\Program.cs:line 18

Steps to reproduce

ctx.Orders.AsQueryable().GroupBy(o => o.Name).Select(g => new { Name = g.Key, cnt = g.Select(o => o.Status).Distinct().Count() }).ToArray();

or

ctx.Orders.AsQueryable().GroupBy(o => o.Name).Select(g => new { Name = g.Key, cnt = g.GroupBy(o => o.Status).Count() }).ToArray();

must translate to

select Name, count(distinct Id) from dbo.Orders group by Name;

Further technical details

EF Core version: 3.0.0-preview9.19421.14
Database Provider: Microsoft.EntityFrameworkCore.SqlServer
Operating system: Windows 8.1
IDE: Visual Studio 2019 16.3 preview 2.0

[smitpatel]

Distinct can be applied in front of anything. Should be made first class like SqlExpression.

[smitpatel]

Design meeting decision, make a wrapper to provide Distinct around any sqlExpression. It does not have to be property on SqlExpression.