Throw a better exception for failed translations (i.e. client evaluation not supported)

[nixxcz]

I'm passing a predicate to LINQ query as Func<>. The resulting expression cannot be, for some reason, translated to SQL. In Preview 5, I get a helpful exception. In Preview 6, I get no clue about what went wrong.

#16101 may be related

I would appreciate suggestions on how to pass the predicate so that it can be translated.
Thank you!

Preview 5 behavior

System.InvalidOperationException
  HResult=0x80131509
  Message=Error generated for warning 'Microsoft.EntityFrameworkCore.Query.QueryClientEvaluationWarning: The LINQ expression 'where Invoke(__predicate_0, [a], ".cz")' could not be translated and will be evaluated locally.'. This exception can be suppressed or logged by passing event ID 'RelationalEventId.QueryClientEvaluationWarning' to the 'ConfigureWarnings' method in 'DbContext.OnConfiguring' or 'AddDbContext'.
  Source=Microsoft.EntityFrameworkCore
  StackTrace:
   at Microsoft.EntityFrameworkCore.Diagnostics.EventDefinition`1.Log[TLoggerCategory](IDiagnosticsLogger`1 logger, WarningBehavior warningBehavior, TParam arg)
   at Microsoft.EntityFrameworkCore.Diagnostics.RelationalLoggerExtensions.QueryClientEvaluationWarning(IDiagnosticsLogger`1 diagnostics, QueryModel queryModel, Object queryModelElement)
   at Microsoft.EntityFrameworkCore.Query.RelationalQueryModelVisitor.WarnClientEval(QueryModel queryModel, Object queryModelElement)
   at Microsoft.EntityFrameworkCore.Query.RelationalQueryModelVisitor.VisitWhereClause(WhereClause whereClause, QueryModel queryModel, Int32 index)
   at Remotion.Linq.Clauses.WhereClause.Accept(IQueryModelVisitor visitor, QueryModel queryModel, Int32 index)
   at Remotion.Linq.QueryModelVisitorBase.VisitBodyClauses(ObservableCollection`1 bodyClauses, QueryModel queryModel)
   at Remotion.Linq.QueryModelVisitorBase.VisitQueryModel(QueryModel queryModel)
   at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.VisitQueryModel(QueryModel queryModel)
   at Microsoft.EntityFrameworkCore.Query.RelationalQueryModelVisitor.VisitQueryModel(QueryModel queryModel)
   at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.CreateQueryExecutor[TResult](QueryModel queryModel)
   at Microsoft.EntityFrameworkCore.Storage.Database.CompileQuery[TResult](QueryModel queryModel)
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.CompileQueryCore[TResult](Expression query, IQueryModelGenerator queryModelGenerator, IDatabase database, IDiagnosticsLogger`1 logger, Type contextType)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.<>c__DisplayClass17_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.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at Vam.Admin.VamData.Playground.Program.Main(String[] args)

Preview 6 behavior

System.InvalidCastException
  HResult=0x80004002
  Message=Unable to cast object of type 'System.Linq.Expressions.InvocationExpression2' to type 'Microsoft.EntityFrameworkCore.Relational.Query.Pipeline.SqlExpressions.SqlExpression'.
  Source=Microsoft.EntityFrameworkCore.Relational
  StackTrace:
   at Microsoft.EntityFrameworkCore.Relational.Query.Pipeline.RelationalSqlTranslatingExpressionVisitor.Translate(Expression expression)
   at Microsoft.EntityFrameworkCore.Relational.Query.Pipeline.RelationalQueryableMethodTranslatingExpressionVisitor.TranslateExpression(Expression expression)
   at Microsoft.EntityFrameworkCore.Relational.Query.Pipeline.RelationalQueryableMethodTranslatingExpressionVisitor.TranslateLambdaExpression(ShapedQueryExpression shapedQueryExpression, LambdaExpression lambdaExpression)
   at Microsoft.EntityFrameworkCore.Relational.Query.Pipeline.RelationalQueryableMethodTranslatingExpressionVisitor.TranslateWhere(ShapedQueryExpression source, LambdaExpression predicate)
   at Microsoft.EntityFrameworkCore.Query.Pipeline.QueryableMethodTranslatingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression)
   at System.Linq.Expressions.MethodCallExpression.Accept(ExpressionVisitor visitor)
   at Microsoft.EntityFrameworkCore.Query.Pipeline.QueryCompilationContext2.CreateQueryExecutor[TResult](Expression query)
   at Microsoft.EntityFrameworkCore.Storage.Database.CompileQuery2[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.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at Vam.Admin.VamData.Playground.Program.Main(String[] args)

Steps to reproduce

var context = new VamContext();

Expression<Func<Account, bool>> predicateExpression1 = a => a.Email.Contains(".cz");
var query1 = context.Account.Where(predicateExpression1);
var results1 = query1.ToList(); //OK

Func<Account, string, bool> predicate = (a, filter) => a.Email.Contains(filter);
Expression<Func<Account, bool>> predicateExpression2 = a => predicate(a, ".cz");
var query2 = context.Account.Where(predicateExpression2);
var results2 = query2.ToList(); //Throws exception

Further technical details

Packages

    <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="3.0.0-preview5.19227.1" />
    <PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="3.0.0-preview5.19227.1">

Operating system: Windows 10 Version 10.0.17763 Build 17763
IDE: VS 2019 16.2.0 Preview 2.0

[smitpatel]

Duplicate of #14572

That being said, second query may not work because of client eval.

[ajcvickers]

@nixxcz Also, many thanks for trying preview 6. We really appreciate people trying the previews and filing issues on what they find.

If you haven't seen it already, there is some good information in the preview announcement post about the changes that are happening to LINQ queries for EF Core 3.0. Preview 6 is the first release containing these changes, which means we are both expecting things to be broken, but at the same time very grateful for everyone who tries the release and generated feedback.

[nixxcz]

Thanks @smitpatel and @ajcvickers for your replies. Does that mean that the more helpful exception from Preview 5 will be coming back in future versions?

In case anyone is interested, I managed to work around the issue by using LinqKit.Microsoft.EntityFrameworkCore and its Expression.Invoke() and Expression.Expand() extension methods:

Func<Account, string, bool> predicate = (a, filter) => a.Email.Contains(filter); //passed from calling code

Expression<Func<Account, bool>> predicateExpression2 = a => predicate.Invoke(a, ".cz");
var query2 = context.Account.Where(predicateExpression2.Expand());

[ajcvickers]

@nixxcz Not sure when the better exception is coming back, but that is the goal.

[smitpatel]

SqlTranslator is also supposed to return null on VisitInvocation.

[smitpatel]

Fixed SqlTranslator to not throw InvalidCastException.