Entity Framework Core，只返回与 Automapper 相关的 id？

Question

I am developing a REST Api using .netCore 3.1, EF Core and Automapper.

I have the following Entities:

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

    [Required]
    [MaxLength(50)]
    public String Name { get; set; }

    [MaxLength(800)]
    public String Description { get; set; }

    [Required]
    public PhaseCategory PhaseCategory { get; set; }
}

and

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

  [MaxLength(50)]
  public String Name { get; set; }
}

and I created the following DTO for the Rest Api Call /api/Phases

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

    public String Name { get; set; }

    public String Description { get; set; }

    public int PhaseCategoryId { get; set; }
}

The issue I have is that in order to make PhaseCategoryId available, I need to query in the following way:

var phase = _dbContext.Phases.Include(pc => pc.PhaseCategory).ToList();
return Ok(_mapper.Map<IEnumerable<PhaseReadDTO>>(phase));

That means that behind the scenes, EF is doing an INNER JOIN that is not needed

SELECT [p].[Id], [p].[Description], [p].[Name], [p].[PhaseCategoryId], [p0].[Id], [p0].[Name]  
    FROM [Phases] AS [p]  
    INNER JOIN [PhaseCategories] AS [p0] ON [p].[PhaseCategoryId] = [p0].[Id]

But when I do

var phase = _dbContext.Phases.ToList();
return Ok(_mapper.Map<IEnumerable<PhaseReadDTO>>(phase));

The query is what I expect

SELECT [p].[Id], [p].[Description], [p].[Name], [p].[PhaseCategoryId]  
            FROM [Phases] AS [p]

But the PhaseCategoryId is not populated in the response.

Answer 1

I guess you have something like the following line in your mapping configuration -

.ForMember(d => d.PhaseCategoryId, opt => MapFrom(s => s.PhaseCategory.Id))

Right?

Since you don't have a property called PhaseCategoryId in your Phase model, you are forcing yourself to load the PhaseCategory property instead to make the mapping happen, and the -

Include(pc => pc.PhaseCategory)

part of your query is causing the Inner Join.

Add the foreign key property -

public int PhaseCategoryId { get; set; }

in your Phase model and define the mapping configuration as simply -

CreateMap<Phase, PhaseReadDTO>();

Then you can query without the Include part and still have the PhaseCategoryId in the response.