使用实体框架核心从Newtonsoft JsonSerializer进行自引用循环 [英] Self referencing loop from Newtonsoft JsonSerializer using Entity Framework Core
问题描述
我遇到了错误:
JsonSerializationException:检测到以下情况的自引用循环 属性"Subject"，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'.
当我加载由IEnumerable<Subject>模型填充的dataGrid的View时，会发生这种情况.网格是绑定到View模型的DevExtreme DataGrid，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
})
)
其中哪个是从Controller填充的，该Controller使用以下功能从存储库中提取数据:
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();
}
主题"表与总计"具有1:1关系，总计"具有对主题"的外键引用.项目中的模型如下所示(从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个对象互相引用，因此在序列化时会导致循环.为了解决这个问题，我将此配置添加到了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了什么: https://stackoverflow.com/a/40501464/7897176
Which I got from this answer: https://stackoverflow.com/a/40501464/7897176
但是，这不能解决问题，并且在加载涉及主题的视图时仍会导致错误.将[JsonIgnore]添加到Totals的Subject属性可以解决此问题，但是我不想将其添加到模型中的每个子属性中，并且每次从数据库更新模型时都不必重做.
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序列化期间的自引用循环问题与EFCore如何加载相关数据有关(
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().
每当获得要序列化的实体的自引用图时，就会有以下几种选择:
Whenever you get a self-referencing graph of entities to be serialized, there are several options:
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.如您所述，当重新生成模型类时，属性消失.因此，它们的使用可能很不方便.
[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):预先选择一部分属性:
(Best choice) Pre-select a subset of properties:
var minimallyNecessarySet= _nwind.Products.Select(p => new {
p.ProductID,
p.ProductName,
p.UnitPrice,
p.CategoryID
});
return minimallyNecessarySet.ToList();
此方法的优点是仅序列化所需的数据.与DevExtreme的DataSourceLoader:
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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