JsonException:检测到不支持的可能对象循环.这可能是由于循环或对象深度大于

问题描述

在我的 web api 中，当我运行从数据库获取数据的项目时出现此错误.net 核心 3.1

In my web api when i run project for get data from database got this error .net core 3.1

JsonException:检测到不支持的可能对象循环.这可能是由于循环或对象深度大于最大允许深度 32 造成的.

JsonException: A possible object cycle was detected which is not supported. This can either be due to a cycle or if the object depth is larger than the maximum allowed depth of 32.

这些是我的代码我的模特

These are my code my Model

 public class Product
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string ProductText { get; set; }
    public int ProductCategoryId { get; set; }
    [JsonIgnore]
    public virtual ProductCategory ProductCategory { get; set; }
}

我的 productCategory 类是:

my productCategory class is:

 public class ProductCategory
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string CatText { get; set; }
    public string ImagePath { get; set; }
    public int Priority { get; set; }
    public int Viewd { get; set; }
    public string Description { get; set; }
    public bool Active { get; set; }
    public DateTime CreateDate { get; set; }
    public DateTime ModifyDate { get; set; }
    public virtual ICollection<Product> Products { get; set; }
}

我的仓库是

public async Task<IList<Product>> GetAllProductAsync()
    {
        return await  _context.Products.Include(p => p.ProductCategory).ToListAsync(); 
    }

我的界面

public interface IProductRepository
{
   ...
    Task<IList<Product>> GetAllProductAsync();
 ...
}

这是我在 api 项目中的控制器

and this is my controller in api project

 [Route("api/[controller]")]
[ApiController]
public class ProductsController : ControllerBase
{
    private readonly IProductRepository _productRepository;

    public ProductsController(IProductRepository productRepository)
    {
        _productRepository = productRepository;
    }
    [HttpGet]
    public ActionResult Get()
    {
        return Ok(_productRepository.GetAllProduct());
    }
}

当我运行 api 项目并输入以下网址时:https://localhost:44397/api/products我得到了那个错误，解决不了

When I run api project and put this url: https://localhost:44397/api/products I got that error , I cant resolve it

推荐答案

这是因为你的数据有一个引用循环.

this is happening because your data have a reference loop.

例如

// this example creates a reference loop
var p = new Product()
     { 
        ProductCategory = new ProductCategory() 
           { products = new List<Product>() }
     };
    p.ProductCategory.products.Add(p); // <- this create the loop
    var x = JsonSerializer.Serialize(p); // A possible object cycle was detected ...

你还不能在新的 System.Text.Json 中处理引用循环情况(netcore 3.1.1)，除非你完全忽略一个引用并且它总是不是一个好主意.(使用 [JsonIgnore] 属性)

You can not handle the reference loop situation in the new System.Text.Json yet (netcore 3.1.1) unless you completely ignore a reference and its not a good idea always. (using [JsonIgnore] attribute)

但您有两种选择来解决此问题.

but you have two options to fix this.

1. 您可以使用 Newtonsoft.Json 在您的项目中，而不是 System.Text.Json(我为您链接了一篇文章)

1. you can use Newtonsoft.Json in your project instead of System.Text.Json (i linked an article for you)

从 dotnet5 库(通过 Visual Studio 的 NuGet 客户端)下载 System.Text.Json 预览包版本 5.0.0-alpha.1.20071.1:

Download the System.Text.Json preview package version 5.0.0-alpha.1.20071.1 from dotnet5 gallery (through Visual Studio's NuGet client):

选项 1 用法:

services.AddMvc()
     .AddNewtonsoftJson(
          options => {
           options.SerializerSettings.ReferenceLoopHandling = ReferenceLoopHandling.Ignore; 
      });
// if you not using .AddMvc use these methods instead 
//services.AddControllers().AddNewtonsoftJson(...);
//services.AddControllersWithViews().AddNewtonsoftJson(...);
//services.AddRazorPages().AddNewtonsoftJson(...);

选项 2 用法:

// for manual serializer
var options = new JsonSerializerOptions
{
    ReferenceHandling = ReferenceHandling.Preserve
};

string json = JsonSerializer.Serialize(objectWithLoops, options);

// -----------------------------------------
// for asp.net core 3.1 (globaly)
 services.AddMvc()
  .AddJsonOptions(o => {
     o.JsonSerializerOptions
       .ReferenceHandling = ReferenceHandling.Preserve  
            });

这些序列化程序具有 ReferenceLoopHandling 功能.

these serializers have ReferenceLoopHandling feature.

• 编辑: ReferenceHandling 在 DotNet 5 中更改为 ReferenceHandler

• Edit : ReferenceHandling changed to ReferenceHandler in DotNet 5

但如果您决定只忽略一个引用，请在这些属性之一上使用 [JsonIgnore].但即使您没有引用循环，它也会导致您对该字段的 API 响应为空.

but if you decide to just ignore one reference use [JsonIgnore] on one of these properties. but it causes null result on your API response for that field even when you don't have a reference loop.

public class Product
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string ProductText { get; set; }
    
    public int ProductCategoryId { get; set; }
    // [JsonIgnore] HERE or
    public virtual ProductCategory ProductCategory { get; set; }
}

public class ProductCategory
{
    public int Id { get; set; }
    // [JsonIgnore] or HERE
    public ICollection<Product> products {get;set;}
}

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