Calling new DateTime() in projection causes NullReferenceException.

[dmitryshunkov]

Calling default DateTime constructor in select method causes NullReferenceException. Need it for example, to convert TimeSpan to DateTime.

Exception message: Object reference not set to an instance of an object.
Stack trace:
   at Microsoft.EntityFrameworkCore.Query.Internal.ExpressionEqualityComparer.GetHashCode(Expression obj)
   at Microsoft.EntityFrameworkCore.Query.Internal.ExpressionEqualityComparer.GetHashCode(Expression obj)
   at Microsoft.EntityFrameworkCore.Query.Internal.ExpressionEqualityComparer.GetHashCode(Expression obj)
   at Microsoft.EntityFrameworkCore.Query.Internal.ExpressionEqualityComparer.GetHashCode(Expression obj)
   at Microsoft.EntityFrameworkCore.Query.Internal.ExpressionEqualityComparer.GetHashCode[T](IList`1 expressions)
   at Microsoft.EntityFrameworkCore.Query.Internal.ExpressionEqualityComparer.GetHashCode(Expression obj)
   at Microsoft.EntityFrameworkCore.Query.CompiledQueryCacheKeyGenerator.CompiledQueryCacheKey.GetHashCode()
   at Microsoft.EntityFrameworkCore.Query.Internal.RelationalCompiledQueryCacheKeyGenerator.RelationalCompiledQueryCacheKey.GetHashCode()
   at Microsoft.EntityFrameworkCore.Query.Internal.SqlServerCompiledQueryCacheKeyGenerator.SqlServerCompiledQueryCacheKey.GetHashCode()
   at System.Collections.Generic.ObjectEqualityComparer`1.GetHashCode(T obj)
   at System.Collections.Concurrent.ConcurrentDictionary`2.TryAdd(TKey key, TValue value)
   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.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at TestEF.Program.Main() in C:\Git\TestEF\TestEF\Program.cs:line 62

using System;
using System.Collections.Generic;
using System.Linq;
using Microsoft.EntityFrameworkCore;

namespace TestEF
{
    public class BloggingContext : DbContext
    {
        public DbSet<Blog> Blogs { get; set; }
        public DbSet<Post> Posts { get; set; }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
            //=> optionsBuilder.UseInMemoryDatabase();
            => optionsBuilder.UseSqlServer(@"Server=(localdb)\mssqllocaldb;Database=WonkyVB;Trusted_Connection=True;");
    }

    public class Blog
    {
        public int Id { get; set; }
        public string Title { get; set; }

        public ICollection<Post> Posts { get; set; }
    }

    public class Post
    {
        public int Id { get; set; }
        public string Title { get; set; }
        public DateTime DateTime { get; set; }

        public int? BlogId { get; set; }
        public Blog Blog { get; set; }
    }

    public class PostDTO
    {
        public DateTime DateTime { get; set; }
        public string Title { get; set; }
    }

    public class Program
    {
        public static void Main()
        {
            using (var context = new BloggingContext())
            {
                context.Database.EnsureDeleted();
                context.Database.EnsureCreated();

                context.Add(new Blog
                {
                    Posts = new List<Post> { new Post { Title = "First" }, new Post { Title = "Second" }, new Post { Title = "Third" } }
                });
                context.SaveChanges();
            }

            using (var context = new BloggingContext())
            {
                Func<DateTime> getDate = () => new DateTime();

                var list = context.Posts.Select(p => new PostDTO
                {
                    DateTime = new DateTime(),                  // Produces NullReferenceException
                    //DateTime = getDate()                      // Works
                    //DateTime = new DateTime(1, 1, 1)          // Works
                }).ToList(); 

                foreach (var post in list)
                {
                    Console.WriteLine(post.DateTime);
                }
            }
        }
    }
}

Further technical details

EF Core version: 1.1.2
Database Provider: Microsoft.EntityFrameworkCore.SqlServer
Operating system: Windows 10
IDE: Visual Studio 2017

[dmitryshunkov]

@smitpatel Still can reproduce with 2.0.0-preview2-final.

[smitpatel]

@dmitryshunkov - As milestone says this was fixed in 2.0.0. So it is expected to reproduce in 2.0.0-preview2-final. Once we release 2.0.0 (which will be very soon), please verify on those packages.

[dmitryshunkov]

Thanks, I was thinking it should be in preview, as fix was on dev branch.

[smitpatel]

@dmitryshunkov - Fixes are (almost) always merged into dev branch. Based on release cycle, at certain point, we take snapshot of dev and generate release package out of it. For a fix to be in a certain release, it has to be merged to dev before we take snapshot. Generally milestone put on issues are better indicator for which release fix will be in. We update milestone based on when fix was merged.