Entity Framework Core：Include 不会在完全定义的关系中加载关系

Question

给定以下三个类：

public class Make
{
    public int MakeId { get; set; }
    [Required]
    [StringLength(255)]
    public string Name { get; set; }
    public ICollection<Model> Models { get; set; }

    public Make()
    {
        Models = new Collection<Model>();
        Name = string.Empty;
    }
}

public class Model
{
    public int ModelId { get; set; }
    [Required]
    [StringLength(255)]
    public string Name { get; set; }
    public Make Make { get; set; }
    public int MakeId { get; set; }

    Model()
    {
        Name = string.Empty;
        Make = new Make();
    }
}

public class VegaDbContext : DbContext
{
    public VegaDbContext(DbContextOptions<VegaDbContext> options) : base(options)
    {

    }
    public DbSet<Make> Makes { get; set; }
    public DbSet<Model> Models { get; set; }
}

我想让一个 API 端点可用，它返回 Make 和相关模型。 function 如下所示：

[HttpGet("/api/makes")]
public async Task<IEnumerable<MakeResource>> GetMakes()
{
    // Here Models is not being loaded!
    var makes = await dbContext.Makes.Include(m => m.Models).ToListAsync();

    // This is manually loading the required data, which works. But I don't want to do this.
    foreach (var make in makes)
    {
        make.Models = await dbContext.Models.Where(m => m.MakeId == make.MakeId).ToListAsync();
    }

    // This mapper part is not of interest
    return mapper.Map<IList<Make>, IList<MakeResource>>(makes);
}

这里的问题是，获取 Makes 的行不包括 Models，而是得到一个空列表。 根据微软的文档，这是一个“完全定义的关系”，应该加载具有正确外键的模型。

随着 EFC 3.0 的引入，似乎发生了一些变化，而且它似乎以前也有效。 我不知道为什么会这样。 如果有人有想法，我会很高兴。 该数据库是使用代码优先迁移创建的：版本是：

.NET Core SDK (reflecting any global.json):
 Version:   3.1.103
 Commit:    6f74c4a1dd

Runtime Environment:
 OS Name:     manjaro
 OS Version:  
 OS Platform: Linux
 RID:         arch-x64
 Base Path:   /usr/share/dotnet/sdk/3.1.103/

Host (useful for support):
  Version: 3.1.3
  Commit:  ed88943d24

.NET Core SDKs installed:
  3.1.103 [/usr/share/dotnet/sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.App 3.1.3 [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 3.1.3 [/usr/share/dotnet/shared/Microsoft.NETCore.App]

To install additional .NET Core runtimes or SDKs:
  https://aka.ms/dotnet-download

数据库中充满：

Answer 1

我能够重现EF Core In-Memory Database Provider的问题，注释掉Make = new Make(); 在Model构造函数中解决了该问题。