使用 Entity Framework Core 的 Newtonsoft JsonSerializer 的自引用循环

Self referencing loop from Newtonsoft JsonSerializer using Entity Framework Core(使用 Entity Framework Core 的 Newtonsoft JsonSerializer 的自引用循环)

问题描述

我遇到了错误:

JsonSerializationException:检测到自引用循环属性主题"，类型为Project.Models.Subject".小路'数据[0].总计'.

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

当我使用由 IEnumerable<Subject> 模型填充的 dataGrid 加载视图时，会发生这种情况.Grid 是一个 DevExtreme DataGrid 绑定到 View 的模型，如下所示:

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
    })
)

从使用此功能从存储库中提取数据的控制器填充:

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();
        }

Subject 表与 Totals 具有 1:1 的关系，其中 Totals 具有对 Subject 的外键引用.项目中的模型如下所示(由 Scaffold-DbContext 生成):

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; }
    }

由于 2 个对象相互引用，因此在序列化时会导致循环.为了纠正这个问题，我将此配置添加到我的 Startup.ConfigureServices 方法中:

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);

我从这个答案中得到:https://stackoverflow.com/a/40501464/7897176

但是，这并不能解决问题，当我加载涉及主题的视图时，它仍然会导致错误.将 [JsonIgnore] 添加到 Totals 的 Subject 属性可以解决问题，但是我不想将其添加到模型中的每个子属性中，并且每当我更新模型时都必须重做数据库.

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.

推荐答案

JSON序列化时自引用循环的问题与EFCore如何加载相关数据有关(docs).加载集合时，相关实体可能会自动填充，也可能不会自动填充，具体取决于先前是否已加载这些对象.它被称为导航属性的自动修复.或者，可以通过 .Include().

The problem of self-referencing loops during JSON serialization is connected to how EFCore loads related data (docs). When you load a collection, related entities may or may not be automatically populated depending on whether or not those object have been previously loaded. It's called automatic fix-up of navigation properties. Alternatively, they may be eagerly loaded via .Include().

当您获得要序列化的实体的自引用图时，有多种选择:

Whenever you get a self-referencing graph of entities to be serialized, there are several options:

• 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.

• Newtonsoft.Json.ReferenceLoopHandling.Ignore (officially recommended). It works but still can result in serializing excessive data if self-reference occurs deep in the hierarchy.

[JsonIgnore] 属性.正如您所指出的，重新生成模型类时属性会消失.因此，它们的使用可能会很不方便.

[JsonIgnore] attribute on navigation properties. As you noted, attributes disappear when model classes are regenerated. Thus, their use can be inconvenient.

(最佳选择)预选属性子集:

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

return minimallyNecessarySet.ToList();

这种方法的优点是只序列化所需的数据.它与 DevExtreme 的 DataSourceLoader 兼容:

This approach has the advantage of serializing only required data. It's compatible with DevExtreme's DataSourceLoader:

return DataSourceLoader.Load(minimallyNecessarySet, loadOptions);

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