Efcore: Projection with parameterized constructor fails

[mnissl]

The following code worked fine with EF Core 2.2, but no longer with EF Core 3:

``` C#
var wrappedEntities = context.Products
.Select(p => new ProductWrapper(p));

The exception text reads: 

> System.InvalidOperationException: 'When called from 'VisitMemberInit', rewriting a node of type 'System.Linq.Expressions.NewExpression' must return a non-null value of the same type. Alternatively, override 'VisitMemberInit' and change it to not visit children of this type.'

Using a parameterless constructor and passing the entity via a public property works:

``` C#
        var wrappedEntities = context.Products
          .Select(p => new ProductWrapper
          {
            Entity = p
          });

Is this a bug or an intended breaking change: Linq queries are no longer evaluated on the client

Further technical details

EF Core version: 3.0.0
Database provider: Microsoft.EntityFrameworkCore.SqlServer
Target framework: .NET Core 3.0
Operating system: Windows 10 1903
IDE: Visual Studio 2019 16.3.9

[ajcvickers]

@mnissl I have not been able to reproduce this--see my code below. Please post a small, runnable project/solution or complete code listing that demonstrates the behavior you are seeing.

```C#
public class Product
{
public int Id { get; set; }
}

public class ProductWrapper
{
public ProductWrapper(Product product)
{
}
}

public class BloggingContext : DbContext
{
protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
optionsBuilder
.UseSqlServer(@"Server=(localdb)\mssqllocaldb;Database=Test;ConnectRetryCount=0");
}

public DbSet<Product> Products { get; set; }

}

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

        context.AddRange(new Product(), new Product());
        context.SaveChanges();
    }

    using (var context = new BloggingContext())
    {
        var wrappedEntities = context.Products.Select(p => new ProductWrapper(p));
    }
}

}
```

[mnissl]

I could reproduce the issue: It doesn't work if you use both a parameterized constructor and an (empty) property initialization list.

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

  public class ProductWrapper
  {
    public string Name { get; set; }

    public ProductWrapper()
    {
    }

    public ProductWrapper(Product product)
    {
    }
  }

  public class BloggingContext : DbContext
  {
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
      optionsBuilder
        .UseSqlServer(@"Server=(localdb)\mssqllocaldb;Database=Test;ConnectRetryCount=0");
    }

    public DbSet<Product> Products { get; set; }
  }

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

        context.AddRange(new Product(), new Product());
        context.SaveChanges();
      }

      using (var context = new BloggingContext())
      {
        // This works!
        context.Products.Select(p => new ProductWrapper()).ToList();

        // This works!
        context.Products.Select(p => new ProductWrapper { }).ToList();

        // This works!
        context.Products.Select(p => new ProductWrapper { Name = "ABC" }).ToList();

        // This works!
        context.Products.Select(p => new ProductWrapper(p)).ToList();

        // This will throw in Debug, but in Release only with attached debugger!?!
        context.Products.Select(p => new ProductWrapper(p) { }).ToList();

        // This will throw in Debug and Release!
        context.Products.Select(p => new ProductWrapper(p) { Name = "ABC" }).ToList();
      }
    }
  }

[AlexTeixeira]

Hello,

Great spot ! It's a quite annoying bug when you develop with on a Clean Architecture/DDD way.

When you think this will be available ?

I have two project ( one new & one migrations ready ) that have this issue, and I waste some time to analyse when the issue come from me or not.

Thanks for the answer

[mnissl]

@smitpatel Would it be possible to have this fix available in EF Core 3.0.x or 3.1? Milestone 5.0.0 sounds like .NET 5 sounds like November 2020!?

[mkontula]

Seriously 5.0.0? Since this is broken between 2.2 and 3.0 it would most appreciated if this would make it to 3.1.0.

[brunosantosrhsenso]

I've stumbled upon this issue as well while converting from 2.2 to 3.0. The fix should come ASAP.

[ajcvickers]

Note from triage: we will consider patching this for a 3.1.x release.