简单地放置Configuration。ProxyCreationEnabled = false;在上下文文件中;这样问题就解决了。

public demEntities()
    : base("name=demEntities")
{
    Configuration.ProxyCreationEnabled = false;
}

最好的解决方案是从Web API中的循环引用处理(这个答案的大部分都是从这里复制的):

修复1:全局忽略循环引用

(我已经选择/尝试了这一个，就像其他许多人一样)

The json.net serializer has an option to ignore circular references. Put the following code in WebApiConfig.cs file: config.Formatters.JsonFormatter.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore; The simple fix will make serializer to ignore the reference which will cause a loop. However, it has limitations: The data loses the looping reference information The fix only applies to JSON.net The level of references can't be controlled if there is a deep reference chain

如果你想在非api的ASP中使用这个修复。NET项目，你可以添加上述行到Global.asax.cs，但首先添加:

var config = GlobalConfiguration.Configuration;

如果你想在.Net Core项目中使用它，你可以将Startup.cs更改为:

var mvc = services.AddMvc(options =>
{
   ...
})
.AddJsonOptions(x => x.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore);

Fix 2: Preserving circular reference globally This second fix is similar to the first. Just change the code to: config.Formatters.JsonFormatter.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Serialize; config.Formatters.JsonFormatter.SerializerSettings.PreserveReferencesHandling = Newtonsoft.Json.PreserveReferencesHandling.Objects; The data shape will be changed after applying this setting. [ { "$id":"1", "Category":{ "$id":"2", "Products":[ { "$id":"3", "Category":{ "$ref":"2" }, "Id":2, "Name":"Yogurt" }, { "$ref":"1" } ], "Id":1, "Name":"Diary" }, "Id":1, "Name":"Whole Milk" }, { "$ref":"3" } ] The $id and $ref keeps the all the references and makes the object graph level flat, but the client code needs to know the shape change to consume the data and it only applies to JSON.NET serializer as well. Fix 3: Ignore and preserve reference attributes This fix is decorate attributes on model class to control the serialization behavior on model or property level. To ignore the property: public class Category { public int Id { get; set; } public string Name { get; set; } [JsonIgnore] [IgnoreDataMember] public virtual ICollection<Product> Products { get; set; } } JsonIgnore is for JSON.NET and IgnoreDataMember is for XmlDCSerializer. To preserve reference: // Fix 3 [JsonObject(IsReference = true)] public class Category { public int Id { get; set; } public string Name { get; set; } // Fix 3 //[JsonIgnore] //[IgnoreDataMember] public virtual ICollection<Product> Products { get; set; } } [DataContract(IsReference = true)] public class Product { [Key] public int Id { get; set; } [DataMember] public string Name { get; set; } [DataMember] public virtual Category Category { get; set; } } JsonObject(IsReference = true)] is for JSON.NET and [DataContract(IsReference = true)] is for XmlDCSerializer. Note that: after applying DataContract on class, you need to add DataMember to properties that you want to serialize. The attributes can be applied on both json and xml serializer and gives more controls on model class.

修复方法是忽略循环引用，不序列化它们。此行为在JsonSerializerSettings中指定。

带重载的单个JsonConvert:

JsonConvert.SerializeObject(YourObject, Formatting.Indented,
    new JsonSerializerSettings() {
        ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore
    }
);

Global.asax.cs中的Application_Start()代码中的全局设置:

JsonConvert.DefaultSettings = () => new JsonSerializerSettings {
     Formatting = Newtonsoft.Json.Formatting.Indented,
     ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore
};

参考:https://github.com/JamesNK/Newtonsoft.Json/issues/78

使用JsonSerializerSettings

ReferenceLoopHandling。如果遇到引用循环，Error(默认)将出错。这就是为什么会出现异常。 ReferenceLoopHandling。如果对象嵌套但不是无限的，序列化是有用的。 ReferenceLoopHandling。如果对象是自身的子对象，Ignore将不会序列化该对象。

例子:

JsonConvert.SerializeObject(YourPOCOHere, Formatting.Indented, 
new JsonSerializerSettings 
{ 
        ReferenceLoopHandling = ReferenceLoopHandling.Serialize
});

如果你必须序列化一个无限嵌套的对象，你可以使用PreserveObjectReferences来避免StackOverflowException。

例子:

JsonConvert.SerializeObject(YourPOCOHere, Formatting.Indented, 
new JsonSerializerSettings 
{ 
        PreserveReferencesHandling = PreserveReferencesHandling.Objects
});

选择对要序列化的对象有意义的内容。

参考http://james.newtonking.com/json/help/

团队:

这适用于ASP。核心网;上面的挑战是如何“设置为忽略”。根据您设置应用程序的方式，这可能相当具有挑战性。以下是对我有效的方法。

这可以放在你的公共void ConfigureServices(IServiceCollection services)部分。

services.AddMvc().AddJsonOptions(opt => 
        { 
      opt.SerializerSettings.ReferenceLoopHandling =
      Newtonsoft.Json.ReferenceLoopHandling.Ignore;
        });

当你有循环问题时，序列化使用NEWTONSOFTJSON，在我的情况下，我不需要修改全局。野蔷薇或野蔷薇。我只是使用JsonSerializesSettings忽略循环处理。

JsonSerializerSettings jss = new JsonSerializerSettings();
jss.ReferenceLoopHandling = ReferenceLoopHandling.Ignore;
var lst = db.shCards.Where(m => m.CardID == id).ToList();
string json = JsonConvert.SerializeObject(lst, jss);