在查询中使用 Select() 而不是 Include() 时出错

Question

I have the following query:

var catInclude = _db.Cat
    .Where(x => x.ProvId == request.ProvId)
    .Include(x => x.CatItems)
    .SingleOrDefault(p => p.Id == request.ProvId
         cancellationToken: cancellationToken);

As I don't want to get all properties from CatItems with Include(), I have created the following query:

var catSelect = _db.Cat
.Where(x => x.ProvId == request.ProvId)
.Select(p ==> new
    { Provider = p,
      Items = p.CatItems.Select(x => new List<CatItems> { new CatItems
{ Id = x.Id, Name = x.Name, Price = x.Price } }
})})
SingleOrDefault(cancellationToken: cancellationToken);

But something is wrong in the 2nd query because here return _mapper.ProjectTo<CatDto>(cat) I get the following error:

Argument 1: cannot convert from '<anonymous type: Db.Entities.Cat Prov, System.Colletions.Generic.IEnumerable<System.Colletions.Generic.List<Models.CatItems> > Items>' to 'System.Linq.IQueryable'

Here is my CatDto :

public class CatDto
{
   public int ProvId { get; set; }
   public List<CatItems> CatItems { get; set; }
}

Here are my entities:

public class Prov
{
   public int Id { get; set; }
   public Cat Cat { get; set; }
}

public class Cat
{
   public int Id { get; set; }
   public int ProvId { get; set; }
   public List<CatItems> CatItems { get; set; }
}

public class CatItems
{
   public int Id { get; set; }
   public int CatId { get; set; }
}

Is there a way to recreate the 2nd query and use it?

Answer 1

I mean, even the exception is pretty self-explanatory. Nevertheless:

You are performing a .Select(...) . It returns an Anonymous type. So, your catSelect is an anonymous type, thus the AutoMapper fails.

The quickest fix is to just cast (Cat)catSelect before mapping.
Or, you can dig deeper into how does AutoMapper play with anonymous types.

Answer 2

Main difference that instead of returning List of CatItems , your code returns IEnumerable<List<CatItems>> for property Items .

So, just correct your query to project to List :

var catSelect = await _db.Cat
    .Where(x => x.ProvId == request.ProvId)
    .Select(p => new
    { 
        Provider = p,
        Items = p.CatItems.Select(x => new CatItems
        { 
            Id = x.Id, 
            Name = x.Name, 
            Price = x.Price 
        })
        .ToList()
    })
    .SingleOrDefaultAsync(cancellationToken: cancellationToken);

Answer 3

I feel like you can make most of the classes inherent Id and why is public cat CAT {get; set;} i thought you were supposed to initialize some kind of value