Issue with NeinLinq.EntityFramework, Linq.Count() method

[TheHACKATHON]

Hi, I have a problem with the Count method in NeinLinq.EntityFramework

Framework: net4.8
EntityFramework: 6.4.4
NeinLinq: 6.1.1
NeinLinq.EntityFramework: 6.1.1

The code looks like this:
I have a query provider:

public interface IQueryProvider<DbContext, TParam, TResult>
{
    [InjectLambda]
    IQueryable<TResult> GetQuery(DbContext context, TParam query);
}

public class GetTodoItemsQueryProvider : IQueryProvider<ApplicationDbContext, int, TodoItem>
{
    [InjectLambda(nameof(GetQueryExpression))]
    public IQueryable<TodoItem> GetQuery(ApplicationDbContext context, int query)
    {
        throw new NotImplementedException();
    }

    public Expression<Func<ApplicationDbContext, int, IQueryable<TodoItem>>> GetQueryExpression()
    {
        return (context, query) => from todoItem in context.Set<TodoItem>()
            where todoItem.ListId == query
            select todoItem;
    }
}

and code which query database and calls this query provider

[HttpGet("test")]
public ActionResult Test()
{
    List<TodoItem> result = (from list in _dbContext.Set<TodoList>().ToDbInjectable()
        let item = _queryProvider.GetQuery(_dbContext, list.Id).FirstOrDefault()
        select item).ToList();

    int count = (from list in _dbContext.Set<TodoList>().ToDbInjectable()
        let item = _queryProvider.GetQuery(_dbContext, list.Id).FirstOrDefault()
        select item).Count();

  return true;
}

the first request(with ToList) works without any problems
on second request I got an exception

LINQ to Entities does not recognize the method 'System.Data.Entity.DbSet`1[TodoList] Set[TodoList]()' method, and this method cannot be translated into a store expression.

Same code on NeinLinq.EntityFrameworkCore works fine, pls help

[axelheer]

That's weird, since the resulting query expressions look almost the same...

List query:

.Call System.Linq.Queryable.Select(
    .Call System.Linq.Queryable.Select(
        .Call .Constant<System.Data.Entity.Core.Objects.ObjectQuery`1[NeinLinq.Tests.TodoList]>(System.Data.Entity.Core.Objects.ObjectQuery`1[NeinLinq.Tests.TodoList]).MergeAs(.Constant<System.Data.Entity.Core.Objects.MergeOption>(AppendOnly))
        ,
        '(.Lambda #Lambda1<System.Func`2[NeinLinq.Tests.TodoList,<>f__AnonymousType3`2[NeinLinq.Tests.TodoList,NeinLinq.Tests.TodoItem]]>))
    ,
    '(.Lambda #Lambda2<System.Func`2[<>f__AnonymousType3`2[NeinLinq.Tests.TodoList,NeinLinq.Tests.TodoItem],NeinLinq.Tests.TodoItem]>))

.Lambda #Lambda1<System.Func`2[NeinLinq.Tests.TodoList,<>f__AnonymousType3`2[NeinLinq.Tests.TodoList,NeinLinq.Tests.TodoItem]]>(NeinLinq.Tests.TodoList $list)
{
    .New <>f__AnonymousType3`2[NeinLinq.Tests.TodoList,NeinLinq.Tests.TodoItem](
        $list,
        .Call System.Linq.Queryable.FirstOrDefault(.Call System.Linq.Queryable.Where(
                .Call (.Constant<NeinLinq.Tests.SomeTest>(NeinLinq.Tests.SomeTest)._dbContext).Set(),
                '(.Lambda #Lambda3<System.Func`2[NeinLinq.Tests.TodoItem,System.Boolean]>))))
}

.Lambda #Lambda2<System.Func`2[<>f__AnonymousType3`2[NeinLinq.Tests.TodoList,NeinLinq.Tests.TodoItem],NeinLinq.Tests.TodoItem]>(<>f__AnonymousType3`2[NeinLinq.Tests.TodoList,NeinLinq.Tests.TodoItem] $<>h__TransparentIdentifier0)
{
    $<>h__TransparentIdentifier0.item
}

.Lambda #Lambda3<System.Func`2[NeinLinq.Tests.TodoItem,System.Boolean]>(NeinLinq.Tests.TodoItem $todoItem) {
    $todoItem.ListId == $list.Id
}

Count query:

.Call System.Linq.Queryable.Count(.Call System.Linq.Queryable.Select(
        .Call System.Linq.Queryable.Select(
            .Call .Constant<System.Data.Entity.Core.Objects.ObjectQuery`1[NeinLinq.Tests.TodoList]>(System.Data.Entity.Core.Objects.ObjectQuery`1[NeinLinq.Tests.TodoList]).MergeAs(.Constant<System.Data.Entity.Core.Objects.MergeOption>(AppendOnly))
            ,
            '(.Lambda #Lambda1<System.Func`2[NeinLinq.Tests.TodoList,<>f__AnonymousType3`2[NeinLinq.Tests.TodoList,NeinLinq.Tests.TodoItem]]>))
        ,
        '(.Lambda #Lambda2<System.Func`2[<>f__AnonymousType3`2[NeinLinq.Tests.TodoList,NeinLinq.Tests.TodoItem],NeinLinq.Tests.TodoItem]>))
)

.Lambda #Lambda1<System.Func`2[NeinLinq.Tests.TodoList,<>f__AnonymousType3`2[NeinLinq.Tests.TodoList,NeinLinq.Tests.TodoItem]]>(NeinLinq.Tests.TodoList $list)
{
    .New <>f__AnonymousType3`2[NeinLinq.Tests.TodoList,NeinLinq.Tests.TodoItem](
        $list,
        .Call System.Linq.Queryable.FirstOrDefault(.Call System.Linq.Queryable.Where(
                .Call (.Constant<NeinLinq.Tests.SomeTest>(NeinLinq.Tests.SomeTest)._dbContext).Set(),
                '(.Lambda #Lambda3<System.Func`2[NeinLinq.Tests.TodoItem,System.Boolean]>))))
}

.Lambda #Lambda2<System.Func`2[<>f__AnonymousType3`2[NeinLinq.Tests.TodoList,NeinLinq.Tests.TodoItem],NeinLinq.Tests.TodoItem]>(<>f__AnonymousType3`2[NeinLinq.Tests.TodoList,NeinLinq.Tests.TodoItem] $<>h__TransparentIdentifier0)
{
    $<>h__TransparentIdentifier0.item
}

.Lambda #Lambda3<System.Func`2[NeinLinq.Tests.TodoItem,System.Boolean]>(NeinLinq.Tests.TodoItem $todoItem) {
    $todoItem.ListId == $list.Id
}

The processing of these expressions is completely different between Entity Framework and Entity Framework Core. Happily the newer Framework understands this anyway.

Nevertheless, NeinLinq does some "clean-up" of the query's expression, which does handle properties but not method calls at the moment. Thus, this should work for you already:

public class GetTodoItemsQueryProvider : IQueryProvider<ApplicationDbContext, int, TodoItem>
{
    [InjectLambda(nameof(GetQueryExpression))]
    public IQueryable<TodoItem> GetQuery(ApplicationDbContext context, int query)
    {
        throw new NotImplementedException();
    }

    public Expression<Func<ApplicationDbContext, int, IQueryable<TodoItem>>> GetQueryExpression()
    {
        return (context, query) => from todoItem in context.TodoItems
                                   where todoItem.ListId == query
                                   select todoItem;
    }
}

I can dig a little deeper to make context.Set<TodoItem>() work as well. Please let me know, if context.TodoItems is sufficient anyway.

Just for further reference, the test code I used in order to reproduce this:

using System.Data.Entity;
using Xunit;

namespace NeinLinq.Tests;

public class SomeTest
{
    private readonly ApplicationDbContext _dbContext;
    private readonly IQueryProvider<ApplicationDbContext, int, TodoItem> _queryProvider;

    public SomeTest()
    {
        _dbContext = new ApplicationDbContext("Data Source=(localdb)\\MSSQLLocalDB;Initial Catalog=SomeTest;Integrated Security=true;");
        _dbContext.TodoLists.Add(
            new TodoList
            {
                Items =
                {
                    new TodoItem()
                }
            }
        );
        _dbContext.SaveChanges();

        _queryProvider = new GetTodoItemsQueryProvider();
    }

    [Fact]
    public void Test_WithLambdaInjection()
    {
        var query = from list in _dbContext.Set<TodoList>().ToDbInjectable()
                    let item = _queryProvider.GetQuery(_dbContext, list.Id).FirstOrDefault()
                    select item;

        var result = query.ToList();

        Assert.NotEmpty(result);

        int count = query.Count();

        Assert.NotEqual(0, count);
    }

    [Fact]
    public void Test_WithoutLambdaInjection()
    {
        var query = from list in _dbContext.Set<TodoList>()
                    let item = (from todoItem in _dbContext.Set<TodoItem>()
                                where todoItem.ListId == list.Id
                                select todoItem).FirstOrDefault()
                    select item;

        var result = query.ToList();

        Assert.NotEmpty(result);

        int count = query.Count();

        Assert.NotEqual(0, count);
    }
}

public class TodoList
{
    public int Id { get; set; }

    public virtual ICollection<TodoItem> Items { get; } = new List<TodoItem>();
}

public class TodoItem
{
    public int Id { get; set; }

    public int ListId { get; set; }

    public virtual TodoList? List { get; set; }
}

public class ApplicationDbContext : DbContext
{
    public DbSet<TodoList> TodoLists { get; }

    public DbSet<TodoItem> TodoItems { get; }

    public ApplicationDbContext(string nameOrConnectionString) : base(nameOrConnectionString)
    {
        TodoLists = Set<TodoList>();
        TodoItems = Set<TodoItem>();
    }
}

public interface IQueryProvider<DbContext, TParam, TResult>
{
    [InjectLambda]
    IQueryable<TResult> GetQuery(DbContext context, TParam query);
}

public class GetTodoItemsQueryProvider : IQueryProvider<ApplicationDbContext, int, TodoItem>
{
    [InjectLambda(nameof(GetQueryExpression))]
    public IQueryable<TodoItem> GetQuery(ApplicationDbContext context, int query)
    {
        throw new NotImplementedException();
    }

    public Expression<Func<ApplicationDbContext, int, IQueryable<TodoItem>>> GetQueryExpression()
    {
        return (context, query) => from todoItem in context.TodoItems
                                   where todoItem.ListId == query
                                   select todoItem;
    }
}

[TheHACKATHON]

Thanks for your research.
сontext.TodoItems works as a workaround for now, but I would like to use Set<>, because in most code we inject abstract DbContext and don't have access to properties like TodoItems, and unit tests now based on Set method

[axelheer]

Okay, after some further digging, it seems, that Entity Framework needs some processing, in order to understand, what you are doing here. This is currently implemented by an internal EF class DbQueryVisitor, which I now call using some Reflection.

I'm not quite happy with this "Hack", but please try Version 6.2.0 as it will be available as a Preview here:
https://github.com/axelheer/nein-linq/pkgs/nuget/NeinLinq.EntityFramework

For implementation details: 66817a2

[TheHACKATHON]

For some reason, I can't see this prerelease on NuGet and can't install it via command
NU1102: Unable to find package NeinLinq.EntityFramework with version (>= 6.2.0-preview.186)

[axelheer]

It isn't on NuGet, the previews are on GitHub only.

See Installing a package for details

[TheHACKATHON]

Thank you. I checked, for my cases the problem is fixed