Self referencing loop from Newtonsoft JsonSerializer using Entity Framework Core

Question

I've encountered the error:

JsonSerializationException: Self referencing loop detected for property 'Subject' with type 'Project.Models.Subject'. Path 'data[0].Totals'.

It occurs when I load a View with a dataGrid populated by an IEnumerable<Subject> model. The Grid is a DevExtreme DataGrid bound to the View's model like this:

@(Html.DevExtreme().DataGrid()
    .DataSource(Model)
    .Paging(paging =>
    {
        paging.Enabled(true);
        paging.PageIndex(0);
        paging.PageSize(20);
    })
    .Columns(columns =>
    {
        columns.Add().DataField("SubjectId");
        ... other fields
    })
)

Which is populated from a Controller that pulls data from a Repository with this function:

public async Task<IEnumerable<Subject>> GetSubjectsAsync()
        {
            return await _context.Subject.ToListAsync();
        }

The Subject table has a 1:1 relationship with Totals with Totals having a foreign key reference to Subject. The Models in the project look like this (generated from Scaffold-DbContext):

public partial class Subject
    {
        public Guid SubjectId { get; set; }
        public virtual Totals Totals { get; set; }
    }

public partial class Totals
    {
        public Guid TotalsId { get; set; }
        public virtual Subject Subject { get; set; }
    }

Since the 2 objects reference eachother it causes a loop when serializing it. To correct this I added this config to my Startup.ConfigureServices method:

services.AddMvc()
                .AddJsonOptions(x => x.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore);

Which I got from this answer: /sf/answers/2835102511/

However this doesn't fix the problem and its still causing an error when I load a view that involves Subjects. Adding [JsonIgnore] to the Subject property of Totals fixes the problem, but I don't want to have to add that to every child property in my models and have to redo it whenever I update my models from the db.

Answer 1

JSON 序列化期间自引用循环的问题与 EFCore 如何加载相关数据 ( docs ) 相关。加载集合时，相关实体可能会或可能不会自动填充，具体取决于这些对象之前是否已加载。这称为导航属性的自动修复。或者，它们可以通过.Include().

每当您获得要序列化的实体的自引用图时，有几种选择：

• Newtonsoft.Json.ReferenceLoopHandling.Ignore（官方推荐）。它可以工作，但如果自引用发生在层次结构的深处，仍然会导致序列化过多的数据。

• [JsonIgnore]导航属性上的属性。正如您所指出的，重新生成模型类时，属性会消失。因此，它们的使用可能不方便。

• （最佳选择）预先选择属性子集：

  var minimallyNecessarySet= _nwind.Products.Select(p => new {
      p.ProductID,
      p.ProductName,
      p.UnitPrice,
      p.CategoryID
  });
  
  return minimallyNecessarySet.ToList();
  

  这种方法的优点是仅序列化所需的数据。它与 DevExtreme 兼容DataSourceLoader：

  return DataSourceLoader.Load(minimallyNecessarySet, loadOptions);