Argument types don't match for queries projecting conditional expression with anonymous type result

[sethen]

I am using a query in my repository which you can view at this gist: https://gist.github.com/sethen/c1f3cb54e50eb36b696a1f4d79d1670c#file-gistfile1-txt-L23 which is similar to the query I found in issue #5522 -- unfortunately I am still getting the same error. Here is my stack trace:

fail: Microsoft.AspNetCore.Server.Kestrel[13]
      Connection id "0HL4DOE8S2AI2": An unhandled exception was thrown by the application.
System.ArgumentException: Argument types do not match
   at System.Linq.Expressions.Expression.Condition(Expression test, Expression ifTrue, Expression ifFalse, Type type)
   at System.Linq.Expressions.ConditionalExpression.Update(Expression test, Expression ifTrue, Expression ifFalse)
   at System.Linq.Expressions.ConditionalExpression.Accept(ExpressionVisitor visitor)
   at Remotion.Linq.Parsing.ThrowingExpressionVisitor.Visit(Expression expression)
   at System.Linq.Enumerable.SelectIListIterator`2.MoveNext()
   at System.Linq.Enumerable.WhereEnumerableIterator`1.MoveNext()
   at System.Collections.Generic.EnumerableHelpers.ToArray[T](IEnumerable`1 source, Int32& length)
   at System.Collections.Generic.EnumerableHelpers.ToArray[T](IEnumerable`1 source)
   at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source)
   at Microsoft.EntityFrameworkCore.Query.ExpressionVisitors.SqlTranslatingExpressionVisitor.VisitNew(NewExpression expression)
   at System.Linq.Expressions.NewExpression.Accept(ExpressionVisitor visitor)
   at Remotion.Linq.Parsing.ThrowingExpressionVisitor.Visit(Expression expression)
   at Microsoft.EntityFrameworkCore.Query.ExpressionVisitors.RelationalProjectionExpressionVisitor.Visit(Expression node)
   at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.VisitSelectClause(SelectClause selectClause, 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)
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.CompileQueryCore[TResult](Expression query, INodeTypeProvider nodeTypeProvider, IDatabase database, ILogger logger, Type contextType)
   at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQueryCore[TFunc](Object cacheKey, Func`1 compiler)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.Execute[TResult](Expression query)
   at Remotion.Linq.QueryableBase`1.System.Collections.IEnumerable.GetEnumerator()
   at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeList(JsonWriter writer, IEnumerable values, JsonArrayContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.Serialize(JsonWriter jsonWriter, Object value, Type objectType)
   at Newtonsoft.Json.JsonSerializer.SerializeInternal(JsonWriter jsonWriter, Object value, Type objectType)
   at Microsoft.AspNetCore.Mvc.Formatters.JsonOutputFormatter.WriteObject(TextWriter writer, Object value)
   at Microsoft.AspNetCore.Mvc.Formatters.JsonOutputFormatter.<WriteResponseBodyAsync>d__9.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.<InvokeResultAsync>d__32.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.<InvokeResultFilterAsync>d__31.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.<InvokeAllResultFiltersAsync>d__29.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.<InvokeResourceFilterAsync>d__23.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.<InvokeAsync>d__18.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.AspNetCore.Builder.RouterMiddleware.<Invoke>d__4.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.AspNetCore.Hosting.Internal.RequestServicesContainerMiddleware.<Invoke>d__3.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Microsoft.AspNetCore.Server.Kestrel.Internal.Http.Frame`1.<RequestProcessingAsync>d__2.MoveNext()
info: Microsoft.AspNetCore.Hosting.Internal.WebHost[2]
      Request finished in 1016.3886ms 200 application/json; charset=utf-8

Essentially I just want to be able to work with nullable properties on my models in a sane way. The issue referenced said that this was fixed but I have tried many ways to get around this and nothing is working.

Further technical details

EF Core version: (found in project.json or packages.config) 1.1.0
Database Provider: Microsoft.EntityFrameworkCore.Sqlite
Operating system: macOS Sierra
IDE: VSCode

[sethen]

Tried upgrading to 1.1.1 to see if it would fix the issue but it didn't.

[smitpatel]

@sethen - Please share your DbContext & model classes esp. Analysis, Comment, Game, Reward, Matchup.

[sethen]

Sorry it took so long for me to respond, I have been busy. Here are the files you requested.

[smitpatel]

@sethen - Thank you for the files. There were few missing pieces but I was able to fill in the blanks and get a repro. I will investigate further to find the root cause.

[smitpatel]

Offending query:

var analysis = db.Analysis.Select(a => new
                                        {
                                            id = a.AnalysisId,
                                            reward = a.RewardId.HasValue
                                                ? new {user_id = a.Reward.UserId}
                                                : null
                                        })
    .ToList();

Classes

public class Reward
{
    public int Id { get; set; }
    public int AnalysisId { get; set; }
    public int UserId { get; set; }
}

public class Analysis
{
    public int AnalysisId { get; set; }
    public int? RewardId { get; set; }
    public Reward Reward { get; set; }
}

Optional nav.

[smitpatel]

Assigning to @maumar

[maumar]

Fixed in 521feb5

[sethen]

Thanks a lot, a few questions:

• Is there a tentative release date for this fix?
• Is there a current workaround for this?

[maumar]

@Eilon might have some info about the dates. In the meantime you should be able to do:

var analysis = db.Analysis.Select(a => new
{
	id = a.AnalysisId,
	(int?)reward = a.Reward.UserId  
})
.ToList()
.Select(a => new { a.id, reward = a.reward != null ? new { user_id = reward } : null }

Basically, you can project the columns that you need in the final result (EF Core will do the null protection logic for you) and then do another Select(...) on the client to convert the flat results into desirable shape.

[Eilon]

2.0.0 preview 2 isn't too far out - next month I think. Or you can grab the nightly builds from https://dotnet.myget.org/gallery/aspnetcore-dev.

[sethen]

@maumar Thanks for this... I found another way around that seems to fit my use case pretty nicely until this is ready for production. This will fetch the reward and ignore if it's null:

reward = _DBContext.Rewards
    .Where(r => r.AnalysisID == a.AnalysisID)
    .Select(r => new
    {
        id = r.RewardID,
        type = r.RewardType.Type,
        value = r.Value
    })
    .SingleOrDefault()

Not ideal, but until 2.0.0 is ready -- it works.