Query: compilation error for queries with Concat on two entities and Count

[maumar]

query:

context.Gears.Concat(context.Gears).Count();

exception:

Expression of type 'System.Collections.Generic.IEnumerable`1[Microsoft.EntityFrameworkCore.Storage.ValueBuffer]' cannot be used for parameter of type 'System.Collections.Generic.IEnumerable`1[System.Object]' of method 'System.Collections.Generic.IEnumerable`1[System.Object] Concat[Object](System.Collections.Generic.IEnumerable`1[System.Object], System.Collections.Generic.IEnumerable`1[System.Object])'
	at System.Linq.Expressions.Expression.ValidateOneArgument(MethodBase method, ExpressionType nodeKind, Expression arg, ParameterInfo pi)
	at System.Linq.Expressions.Expression.Call(MethodInfo method, Expression arg0, Expression arg1)
	C:\git\EntityFramework\src\EFCore\Query\ResultOperatorHandler.cs(531,0): at Microsoft.EntityFrameworkCore.Query.ResultOperatorHandler.HandleSetOperation(EntityQueryModelVisitor entityQueryModelVisitor, Expression secondSource, MethodInfo setMethodInfo)
	C:\git\EntityFramework\src\EFCore\Query\ResultOperatorHandler.cs(144,0): at Microsoft.EntityFrameworkCore.Query.ResultOperatorHandler.HandleConcat(EntityQueryModelVisitor entityQueryModelVisitor, ConcatResultOperator concatResultOperator)
	C:\git\EntityFramework\src\EFCore\Query\ResultOperatorHandler.cs(36,0): at Microsoft.EntityFrameworkCore.Query.ResultOperatorHandler.<>c.<.cctor>b__33_4(EntityQueryModelVisitor v, ResultOperatorBase r, QueryModel __)
	C:\git\EntityFramework\src\EFCore\Query\ResultOperatorHandler.cs(89,0): at Microsoft.EntityFrameworkCore.Query.ResultOperatorHandler.HandleResultOperator(EntityQueryModelVisitor entityQueryModelVisitor, ResultOperatorBase resultOperator, QueryModel queryModel)
	C:\git\EntityFramework\src\EFCore.Relational\Query\Internal\RelationalResultOperatorHandler.cs(68,0): at Microsoft.EntityFrameworkCore.Query.Internal.RelationalResultOperatorHandler.HandlerContext.EvalOnClient(Boolean requiresClientResultOperator)
	C:\git\EntityFramework\src\EFCore.Relational\Query\Internal\RelationalResultOperatorHandler.cs(156,0): at Microsoft.EntityFrameworkCore.Query.Internal.RelationalResultOperatorHandler.HandleResultOperator(EntityQueryModelVisitor entityQueryModelVisitor, ResultOperatorBase resultOperator, QueryModel queryModel)
	C:\git\EntityFramework\src\EFCore\Query\EntityQueryModelVisitor.cs(1139,0): at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.VisitResultOperator(ResultOperatorBase resultOperator, QueryModel queryModel, Int32 index)
	C:\git\EntityFramework\src\EFCore.Relational\Query\RelationalQueryModelVisitor.cs(1133,0): at Microsoft.EntityFrameworkCore.Query.RelationalQueryModelVisitor.VisitResultOperator(ResultOperatorBase resultOperator, QueryModel queryModel, Int32 index)
	at Remotion.Linq.QueryModelVisitorBase.VisitResultOperators(ObservableCollection`1 resultOperators, QueryModel queryModel)
	at Remotion.Linq.QueryModelVisitorBase.VisitQueryModel(QueryModel queryModel)
	C:\git\EntityFramework\src\EFCore\Query\EntityQueryModelVisitor.cs(694,0): at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.VisitQueryModel(QueryModel queryModel)
	C:\git\EntityFramework\src\EFCore.Relational\Query\RelationalQueryModelVisitor.cs(266,0): at Microsoft.EntityFrameworkCore.Query.RelationalQueryModelVisitor.VisitQueryModel(QueryModel queryModel)
	C:\git\EntityFramework\src\EFCore\Query\EntityQueryModelVisitor.cs(176,0): at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.CreateQueryExecutor[TResult](QueryModel queryModel)
	C:\git\EntityFramework\src\EFCore\Storage\Database.cs(70,0): at Microsoft.EntityFrameworkCore.Storage.Database.CompileQuery[TResult](QueryModel queryModel)
	C:\git\EntityFramework\src\EFCore\Query\Internal\QueryCompiler.cs(139,0): at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.CompileQueryCore[TResult](Expression query, INodeTypeProvider nodeTypeProvider, IDatabase database, IDiagnosticsLogger`1 logger, Type contextType)
	C:\git\EntityFramework\src\EFCore\Query\Internal\QueryCompiler.cs(103,0): at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.<>c__DisplayClass15_0`1.<Execute>b__0()
	C:\git\EntityFramework\src\EFCore\Query\Internal\CompiledQueryCache.cs(69,0): at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQueryCore[TFunc](Object cacheKey, Func`1 compiler)
	C:\git\EntityFramework\src\EFCore\Query\Internal\CompiledQueryCache.cs(44,0): at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQuery[TResult](Object cacheKey, Func`1 compiler)
	C:\git\EntityFramework\src\EFCore\Query\Internal\QueryCompiler.cs(99,0): at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.Execute[TResult](Expression query)
	C:\git\EntityFramework\src\EFCore\Query\Internal\EntityQueryProvider.cs(62,0): at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryProvider.Execute[TResult](Expression expression)
	at System.Linq.Queryable.Count[TSource](IQueryable`1 source)

This happens because requies materialization detects that result converges to single value, and therefore query sources don't need to be materialized - however our current implementation of Concat/Union/Except/Intersect needs those query sources to be materialized, because the translation is on the client.

We should add compensation logic to cover this until we can properly translate those result operators to sql

[smitpatel]

Can you post QueryModel for either of the issue?

[maumar]

fixed in e1d7b16