ToDictionary won't work, if using with navigation property

[Dev0033]

model from https://docs.microsoft.com/en-us/ef/core/get-started/full-dotnet/new-db

If I try to get #Dictionary and navigation property from query, I'll get an exception.

Exception message:

No coercion operator is defined between types 'Intro.Blog' and 'System.String'.

Stack trace:

   at System.Linq.Expressions.Expression.GetUserDefinedCoercionOrThrow(ExpressionType coercionType, Expression expression, Type convertToType)
   at System.Linq.Expressions.Expression.Convert(Expression expression, Type type, MethodInfo method)
   at System.Linq.Expressions.Expression.Convert(Expression expression, Type type)
   at Remotion.Linq.Parsing.RelinqExpressionVisitor.<AdjustArgumentsForNewExpression>d__0.MoveNext()
   at System.Collections.Generic.LargeArrayBuilder`1.AddRange(IEnumerable`1 items)
   at System.Collections.Generic.EnumerableHelpers.ToArray[T](IEnumerable`1 source)
   at System.Dynamic.Utils.CollectionExtensions.ToReadOnly[T](IEnumerable`1 enumerable)
   at System.Linq.Expressions.Expression.New(ConstructorInfo constructor, IEnumerable`1 arguments, IEnumerable`1 members)
   at Remotion.Linq.Parsing.RelinqExpressionVisitor.VisitNew(NewExpression expression)
   at System.Linq.Expressions.NewExpression.Accept(ExpressionVisitor visitor)
   at Microsoft.EntityFrameworkCore.Query.EntityQueryModelVisitor.TrackEntitiesInResults[TResult](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, IDiagnosticsLogger`1 logger, Type contextType)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.<>c__DisplayClass15_0`1.<Execute>b__0()
   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.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 System.Linq.SystemCore_EnumerableDebugView`1.get_Items()

Steps to reproduce

using Intro;
using System;
using System.Linq;

namespace ConsoleApp2
{
  class Program
  {
    static void Main(string[] args)
    {
      using (var db = new BloggingContext())
      {

        if (!db.Blogs.Any())
        {
          db.Blogs.Add(new Blog { Url = "http://Blog1.com" });
          db.Blogs.Add(new Blog { Url = "http://Blog2.com" });
          db.SaveChanges();
        }

        Console.WriteLine("All blogs in database:");

        var query = db.Blogs.Select(c => new
        {
          Url = c.Url,
          Navigation = c,
          Posts = c.Posts.ToDictionary(a => a.PostId.ToString(), x => x.Title),
        });

        foreach (var blog in query)
        {
          Console.WriteLine(" - {0}", blog.Url);
        }
      }
      Console.ReadKey();
    }
  }
}

Workaround

change order of selected fields.
With query:

var query = db.Blogs.Select(c=>new
        {
          Url = c.Url,
          Posts = c.Posts.ToDictionary(a=>a.PostId.ToString(),x=>x.Title),
          Navigation = c,
        });

I can get what I want.

Further technical details

EF Core version: 2.0.1
Database Provider: Microsoft.EntityFrameworkCore.SqlServer
Operating system: Windows 10
IDE: Visual Studio 2017 Enterprise

[smitpatel]

Correct QM

dbug: Microsoft.EntityFrameworkCore.Query[100104]
      Optimized query model:
      'from Blog c in DbSet<Blog>
      order by Property([c], "Id") asc
      select new <>f__AnonymousType0<string, Dictionary<string, string>, Blog>(
          [c].Url,
          Dictionary<string, string> ToDictionary(
              source: List<Post> _ProjectCollectionNavigation(
                  entity: Blog _Include(
                      queryContext: queryContext,
                      entity: [c],
                      included: new object[]{ },
                      fixup: (QueryContext queryContext | Blog entity | Object[] included) =>
                      {
                          Void queryContext.QueryBuffer.StartTracking(
                              entity: entity,
                              entityType: EntityType: Blog)
                          return Void queryContext.QueryBuffer.IncludeCollection(
                              includeId: 0,
                              navigation: Blog.Posts,
                              inverseNavigation: null,
                              targetEntityType: EntityType: Post,
                              clrCollectionAccessor: ClrICollectionAccessor<Blog, List<Post>, Post>,
                              inverseClrPropertySetter: null,
                              tracking: True,
                              instance: entity,
                              valuesFactory: () =>
                                  from Post c.Posts in DbSet<Post>
                                  join AnonymousObject _c in
                                      from Blog c in DbSet<Blog>
                                      select new AnonymousObject(new object[]{ (object)EF.Property(?[c]?, "Id") })
                                  on Property([c.Posts], "BlogId") equals (Nullable<int>)object [_c].GetValue(0)
                                  order by object [_c].GetValue(0) asc
                                  select [c.Posts])
                      }
                  ),
                  accessor: (Blog c) => c?.Posts ?? List<Post>
                  {
                  }
              ),
              keySelector: (Post a) => string a.PostId.ToString(),
              elementSelector: (Post x) => x.Title),
          [c]
      )'

Faulty QM

dbug: Microsoft.EntityFrameworkCore.Query[100104]
      Optimized query model:
      'from Blog c in DbSet<Blog>
      order by Property([c], "Id") asc
      select new <>f__AnonymousType0<string, Blog, Dictionary<string, string>>(
          Blog _Include(
              queryContext: queryContext,
              entity: [c],
              included: new object[]{ },
              fixup: (QueryContext queryContext | Blog entity | Object[] included) =>
              {
                  Void queryContext.QueryBuffer.StartTracking(
                      entity: entity,
                      entityType: EntityType: Blog)
                  return Void queryContext.QueryBuffer.IncludeCollection(
                      includeId: 0,
                      navigation: Blog.Posts,
                      inverseNavigation: null,
                      targetEntityType: EntityType: Post,
                      clrCollectionAccessor: ClrICollectionAccessor<Blog, List<Post>, Post>,
                      inverseClrPropertySetter: null,
                      tracking: True,
                      instance: entity,
                      valuesFactory: () =>
                          from Post c.Posts in DbSet<Post>
                          join AnonymousObject _c in
                              from Blog c in DbSet<Blog>
                              select new AnonymousObject(new object[]{ (object)EF.Property(?[c]?, "Id") })
                          on Property([c.Posts], "BlogId") equals (Nullable<int>)object [_c].GetValue(0)
                          order by object [_c].GetValue(0) asc
                          select [c.Posts])
              }
          ).Url,
          [c],
          Dictionary<string, string> ToDictionary(
              source: List<Post> _ProjectCollectionNavigation(
                  entity: [c],
                  accessor: (Blog c) => c?.Posts ?? List<Post>
                  {
                  }
              ),
              keySelector: (Post a) => string a.PostId.ToString(),
              elementSelector: (Post x) => x.Title)
      )'

Seems like error in _Include optimization or TrackEntitiesInResults

[maumar]

This works in current bits, now using correlated collection optimizations rather than Include pipeline, which was source of the problem.

Current QM:

from Blog c in DbSet<Blog>
order by (Nullable<int>)EF.Property(?[c]?, "Id") asc
select new <>f__AnonymousType0<string, Blog, Dictionary<string, string>>(
    [c].Url, 
    [c], 
    Dictionary<string, string> ToDictionary(
        source: (List<Post>)List<Post> queryContext.QueryBuffer.CorrelateSubquery(
            correlatedCollectionId: 0, 
            navigation: Blog.Posts, 
            resultCollectionFactory: (INavigation n) => (List<Post>)object IClrCollectionAccessor GetCollectionAccessor(n).Create(), 
            outerKey: new MaterializedAnonymousObject(new object[]{ (object)EF.Property(?[c]?, "Id") }), 
            tracking: True, 
            correlatedCollectionFactory: () => 
                from Post c.Posts in DbSet<Post>
                join MaterializedAnonymousObject _c in 
                    from Blog c in DbSet<Blog>
                    select new MaterializedAnonymousObject(new object[]{ (object)(Nullable<int>)EF.Property(?[c]?, "Id") })
                on Property([c.Posts], "BlogId") equals (Nullable<int>)object [_c].GetValue(0)
                order by object [_c].GetValue(0) asc
                select new Tuple<Post, MaterializedAnonymousObject, MaterializedAnonymousObject>(
                    [c.Posts], 
                    new MaterializedAnonymousObject(new object[]{ (object)EF.Property(?[c.Posts]?, "BlogId") }), 
                    new MaterializedAnonymousObject(new object[]{ object [_c].GetValue(0) })
                ), 
            correlationPredicate: (MaterializedAnonymousObject o | MaterializedAnonymousObject i) => object i.GetValue(0) == default(object) || object o.GetValue(0) == default(object) ? False : (Nullable<int>)(int)object o.GetValue(0) == (Nullable<int>)object i.GetValue(0)), 
        keySelector: (Post a) => string a.Id.ToString(), 
        elementSelector: (Post x) => x.Title)
)