Asp.Net Core / Entity Framework Core - System.Linq.Enumerable+SelectEnumerableIterator`2[MyClass,System.String]

Question

I am trying to return a json array of my 3rd level depth related data, the issue here is that I get the result with the right property name but with a non clear value content, I failed to find a similar case to solve it. From the returned value message it looks like I am returning a queryable instead of the final result and I need to iterate over it, I've tried several ways to achive that but failed to find the right one.

The json result:

[
{
"registeredYear": "System.Linq.Enumerable+SelectEnumerableIterator`2[MyPath.Groups.GroupYear,System.String]"
}
]

The api endpoint

public async Task<ActionResult<IEnumerable<UserGroup>>> GetUserGroupYears(string email, string groupName)
    {
        var groupYears = await _repo.GetUserGroupYears(email, groupName);
        var mappedEntities = _mapper.Map<GroupYearsListDto[]>(groupYears);
        return Ok(mappedEntities);
    }

The Repository method

public async Task<IEnumerable<UserGroup>> GetUserGroupYears(string email, string groupName)
{
    var userGroupYears = _context.UserGroups
                          .Include(uo => uo.Group.GroupYears)
                            .ThenInclude( oy => oy.Year)
                          .Where(uo => uo.Group.Name == groupName && uo.Email == email );
            return await userGoupYears.ToArrayAsync();
}

The used classes:

public class UserGroup
{
    public string Email { get; set; }
    
    public string UserId { get; set; }
    public virtual User User { get; set; }
    
    public string GroupId { get; set; }
    public virtual Group Group { get; set; }
}

public class Group
{
    public string Name { get; set; }
    public virtual ICollection<UserGroup> Users { get; set; }
    public virtual ICollection<GroupYear> GroupYears { get; }
}

public class GroupYear    {
    public string GroupId { get; set; }
    public virtual Group Group { get; set; }

    public string YearId { get; set; }
    public virtual Year Year { get; set; }
    public string RegisteredYear { get; set; }
}

The data transfer object and the mapping:

public class GroupYearsListDto
{
    public string RegisteredYear { get; set; }
}
public CoreMappingProfiles()
{
    CreateMap<UserGroup, GroupYearsListDto>()
      .ForMember(
          dest => dest.RegisteredYear,
          opt => opt.MapFrom(src => src.Group.GroupYears.Select(x => x.RegisteredYear))
          );                  
}

Update : Attaching a debugger shows that the repository method is returning an IQueryable including the correct values and the controller method makes something wrong when mapping. So I think the following line is responsible of that wrong result:

var mappedEntities = _mapper.Map<GroupYearsListDto[]>(GroupYears);

Answer 1

You are getting this JSON result:

[
  {
    "registeredYear": "System.Linq.Enumerable+SelectEnumerableIterator`2[MyPath.Groups.GroupYear,System.String]"
  }
]

Because you are mapping an IEnumerable<string> to a string , as I mentioned in my comment. So essentially you are getting the same as:

CreateMap<UserGroup, GroupYearsListDto>()
    .ForMember(
        dest => dest.RegisteredYear,
        opt => opt.MapFrom(src =>
        {
            IEnumerable<string> registeredYears = src.Group.GroupYears.Select(x => x.RegisteredYear);
            return registeredYears.ToString();
        })
    );

And registeredYears.ToString() is "System.Linq.Enumerable+SelectEnumerableIterator`2[MyPath.Groups.GroupYear,System.String]" .

I imagine you will either:

1. Only have one - so do something like: src.Group.GroupYears.Select(x => x.RegisteredYear).Single()
2. Have multiples - so do something like: string.Join(", ", src.Group.GroupYears.Select(x => x.RegisteredYear))

You have many options, but you need to actually return a string to that property or else you will just get the ToString() version of IEnumerable<string> .

UPDATE:

Based on your comments below, you can try this:

Repository:

public IQueryable<GroupYear> GetGroupYears(string email, string groupName)
{
    return _context
        .UserGroups
        .Where(x => x.Group.Name == groupName && x.Email == email)
        .SelectMany(x => x.Group.GroupYears);
}

Controller:

public async Task<ActionResult<GroupYearsListDto[]>> GetGroupYears(string email, string groupName)
{
    var groupYears = _repo.GetGroupYears(email, groupName);
    var projection = _mapper.ProjectTo<GroupYearsListDto>(groupYears)
    var mappedEntities = await projection.ToArrayAsync();
    return Ok(mappedEntities);
}

Profile:

CreateMap<GroupYears, GroupYearsListDto>();