为什么实体框架在MVC应用中的预期行为，而在WebAPI中完全不同？

Question

我已经与Entity Framework 6合作了一段时间，今天我从一个新的Web API项目开始，并且一旦执行包括其他实体的查询，我会收到这样的错误：

system.text.json.jsonexception：检测到可能的对象周期。这可能是由于一个周期引起的，或者如果对象深度大于最大允许的深度32。

。

事物和不明白的是，当我在运行常规MVC应用时使用相同的急切加载时，它将带给我准确我需要什么，别无其他。

到目前为止，这是我正在使用的相关代码：

beer.cs

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

    [Required, StringLength(100)]
    public string Name { get; set; } = null!;
    
    public int BrandId { get; set; }

    public virtual Brand Brand { get; set; } = null!;
}

brand.cs

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

    [Required, StringLength(100)]
    public string Name { get; set; } = null!;

    public virtual ICollection<Beer> Beers { get; set;} = null!;
}

beerrepository.cs

public class BeerRepository : IBeerRepository
{
    private readonly BeerContext _context;

    public BeerRepository(BeerContext context)
    {
        _context = context;
    }

    public async Task CreateBeerAsync(Beer beer)
    {
        if(beer == null)
            throw new ArgumentNullException(nameof(beer));

        await _context.Beers.AddAsync(beer);
    }

    //BUG: This is the one causing me issues!
    public async Task<ICollection<Beer>> GetAsync() => await _context.Beers.Include(b => b.Brand).ToListAsync();

    public async Task<Beer> GetByIdAsync(int id) => await _context.Beers.FirstAsync(b => b.Id == id);

    public async Task SavaChangesAsync()
    {
        await _context.SaveChangesAsync();
    }
}

beercontext.cs

#nullable disable
public partial class BeerContext : DbContext
{
    public DbSet<Beer> Beers { get; set; }
    public DbSet<Brand> Brands { get; set; }

    public BeerContext(DbContextOptions opt) : base(opt)
    {
    }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        //BEER ENTITY
        modelBuilder.Entity<Beer>(entity => {
            entity.HasData(
                new Beer { Id = 1, BrandId = 1, Name = "Torobayo" },
                new Beer { Id = 2, BrandId = 1, Name = "Bock" },
                new Beer { Id = 3, BrandId = 1, Name = "Lager Sin Filtrar" },
                new Beer { Id = 4, BrandId = 2, Name = "Super Dry" },
                new Beer { Id = 5, BrandId = 2, Name = "Soukai" }
            );
        });

        //BRAND ENTITY
        modelBuilder.Entity<Brand>(entity => {
            entity.HasData(
                new Brand{ Id = 1, Name = "Kunstman" },
                new Brand{ Id = 2, Name = "Asahi" }
            );
        });

        OnModelCreatingPartial(modelBuilder);
    }

    partial void OnModelCreatingPartial(ModelBuilder modelBuilder);
}

beerscontroller.cs

[Route("api/[controller]")]
[ApiController]
public class BeersController : ControllerBase
{
    private readonly IBeerRepository _repository;
    private readonly IMapper _mapper;

    public BeersController(IMapper mapper, IBeerRepository repository)
    {
        _mapper = mapper;
        _repository = repository;
    }

    [HttpGet]
    public async Task<ActionResult<IEnumerable<BeerReadDTO>>> GetAllBeers()
    {
        var beers = await _repository.GetAsync();
        return Ok(_mapper.Map<IEnumerable<BeerReadDTO>>(beers));
    }
}

我也更改了program.cs文件

builder.Services.AddControllers().AddJsonOptions(opt => {
    opt.JsonSerializerOptions.ReferenceHandler = ReferenceHandler.IgnoreCycles;
});

。但是相反，我得到了这个“不错的”数据！

[
  {
    "id": 1,
    "name": "Torobayo",
    "brand": {
      "id": 1,
      "name": "Kunstman",
      "beers": [
        {
          "id": 1,
          "name": "Torobayo",
          "brandId": 1,
          "brand": null
        },
        {
          "id": 2,
          "name": "Bock",
          "brandId": 1,
          "brand": null
        },
        {
          "id": 3,
          "name": "Lager Sin Filtrar",
          "brandId": 1,
          "brand": null
        }
      ]
    }
  },
  {
    "id": 2,
    "name": "Bock",
    "brand": {
      "id": 1,
      "name": "Kunstman",
      "beers": [
        {
          "id": 1,
          "name": "Torobayo",
          "brandId": 1,
          "brand": null
        },
        {
          "id": 2,
          "name": "Bock",
          "brandId": 1,
          "brand": null
        },
        {
          "id": 3,
          "name": "Lager Sin Filtrar",
          "brandId": 1,
          "brand": null
        }
      ]
    }
  },
  {
    "id": 3,
    "name": "Lager Sin Filtrar",
    "brand": {
      "id": 1,
      "name": "Kunstman",
      "beers": [
        {
          "id": 1,
          "name": "Torobayo",
          "brandId": 1,
          "brand": null
        },
        {
          "id": 2,
          "name": "Bock",
          "brandId": 1,
          "brand": null
        },
        {
          "id": 3,
          "name": "Lager Sin Filtrar",
          "brandId": 1,
          "brand": null
        }
      ]
    }
  },
  {
    "id": 4,
    "name": "Super Dry",
    "brand": {
      "id": 2,
      "name": "Asahi",
      "beers": [
        {
          "id": 4,
          "name": "Super Dry",
          "brandId": 2,
          "brand": null
        },
        {
          "id": 5,
          "name": "Soukai",
          "brandId": 2,
          "brand": null
        }
      ]
    }
  },
  {
    "id": 5,
    "name": "Soukai",
    "brand": {
      "id": 2,
      "name": "Asahi",
      "beers": [
        {
          "id": 4,
          "name": "Super Dry",
          "brandId": 2,
          "brand": null
        },
        {
          "id": 5,
          "name": "Soukai",
          "brandId": 2,
          "brand": null
        }
      ]
    }
  }
]

这是在后台运行的查询...

info: Microsoft.EntityFrameworkCore.Database.Command[20101]
      Executed DbCommand (49ms) [Parameters=[], CommandType='Text', CommandTimeout='30']
      SELECT [b].[Id], [b].[BrandId], [b].[Name], [b0].[Id], [b0].[Name]
      FROM [Beers] AS [b]
      INNER JOIN [Brands] AS [b0] ON [b].[BrandId] = [b0].[Id]

我实际上需要的是：

[
  {
    "id": 1,
    "name": "Torobayo",
    "brand":"Kunstman"
  },
  {
    "id": 2,
    "name": "Bock",
    "brand":"Kunstman"
  },
  {
    "id": 3,
    "name": "Lager Sin Filtrar",
    "brand":"Kunstman"
  },
  {
    "id": 4,
    "name": "Super Dry",
    "brand":"Asahi"
  },
]

自从我用完的想法以来，任何帮助都是一个好的开始。非常感谢！

编辑： 因此，我决定还发布我的DTO文件以及自动应用程序配置...似乎尚不清楚我实际上是从啤酒实体到相应的DTO绘制的。

BEERREADDTO.CS

public class BeerReadDTO
{
    public int Id { get; set; }
    public string Name { get; set; }
    public Brand Brand { get; set; }
}

AUTOMAPPERCONF.CS

public class AutoMapperConf : Profile
{
    public AutoMapperConf()
    {
        // Source -> Target
        CreateMap<Beer,BeerReadDTO>();
    }
}

Answer 1

好的..谢谢 kamran khan 他指向我朝正确的方向指向正确的方向！...将导航属性从品牌删除到啤酒，并将DTO品牌更改为字符串。

这是我更改的文件，它运行良好！

public class Brand
{
    [Key]
    public int Id { get; set; }

    [Required, StringLength(100)]
    public string Name { get; set; } = null!;

    //public virtual ICollection<Beer> Beers { get; set;} = null!;
}

public class BeerReadDTO
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Brand { get; set; }
}

public class AutoMapperConf : Profile
{
    public AutoMapperConf()
    {
        // Source -> Target
        CreateMap<Beer,BeerReadDTO>()
            .ForMember(d => d.Brand, opt => opt.MapFrom(src => src.Brand.Name));
    }
}

非常感谢！