why In web api returning an entity that has a one to many relationship causes an error?

Question

Guys I have a One to many relation to same class called user,
I am returning one instance of user in web apis get method it works fine as far as I don't have any

User 

ID  | Name 
0   | A 
1   | B 

Friends Table ( This table is used to build the one to many relationship ) 

User_ID | Friend_ID 
 1      |     0 
 0      |     1

This is my GetMethod

[HttpGet]
        public Models.User   Authenticate()
        {
            try
            {
                return   db.Users.SingleOrDefault(x => x.ID == 0 ) ; 
            } 
            catch
            {
                return null;
            }
        }

If I get and return a User entity then I get the blow error

Can anyone please help me to fix this below error ?

{"Message":"An error has occurred.","ExceptionMessage":"The 'ObjectContent`1' type failed to serialize the response body for content type 'text/html; charset=utf-8'.","ExceptionType":"System.InvalidOperationException","StackTrace":null,"InnerException":{"Message":"An error has occurred.","ExceptionMessage":"Self referencing loop detected with type 'System.Data.Entity.DynamicProxies.Friend_E5C79F4736EB2750392FFC7061B18E9C12F15F9583409603C75C5D1B1F7358D4'. Path 'Friends1[0].User.Friends'.","ExceptionType":"Newtonsoft.Json.JsonSerializationException","StackTrace":" at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.CheckForCircularReference(JsonWriter writer, Object value, JsonProperty property, JsonContract contract, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeList(JsonWriter writer, IWrappedCollection values, JsonArrayContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeList(JsonWriter writer, IWrappedCollection values, JsonArrayContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty)\r\n at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.Serialize(JsonWriter jsonWriter, Object value)\r\n at Newtonsoft.Json.JsonSerializer.SerializeInternal(JsonWriter jsonWriter, Object value)\r\n at Newtonsoft.Json.JsonSerializer.Serialize(JsonWriter jsonWriter, Object value)\r\n at System.Net.Http.Formatting.JsonMediaTypeFormatter.<>c__DisplayClassd.b__c()\r\n at System.Threading.Tasks.TaskHelpers.RunSynchronously(Action action, CancellationToken token)"}}

Updated my Question , I have added my GetMethod to the question — Kas, Oct 29 '13 at 16:48
Actully , I am using a Guid as ID ,But in my question i said it as an int field , because I am thinking that the error is not causing because of the guide , however I am expecting a good solution from someone :) — Kas, Oct 29 '13 at 16:49
Can you try exec query and don't return noting, it seems you have error in you models. Try this: var t = db.Users.SingleOrDefault(x => x.ID == 0); return (User)null; — alexmac, Oct 29 '13 at 16:51
This returns the User with ID zero , But it doesn't return from web-api , I am requesting json format as return type of web-api , I was debugging the get method , And I can get the correct user entity, but when return it from web-api , I get that error — Kas, Oct 29 '13 at 16:53
My Model & User classes are slightly complex than the one I showed for the question — Kas, Oct 29 '13 at 16:55
Try decorating your models with `[DataContract(IsReference = true)]` — Aidin, Oct 29 '13 at 17:56
Aidin , that didn't help , I can see only id in result when i decorate my model with DataContract(IsReference = true) — Kas, Oct 30 '13 at 02:48

score 31 · Accepted Answer · answered Oct 29 '13 at 16:58

31

Try to change webApi formatter. Add these lines in WebApiConfig.cs:

var json = config.Formatters.JsonFormatter;
json.SerializerSettings.PreserveReferencesHandling = Newtonsoft.Json.PreserveReferencesHandling.Objects;
config.Formatters.Remove(config.Formatters.XmlFormatter);

And add this line:

json.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore

answered Oct 29 '13 at 16:58

alexmac

19,087
7
58
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3

Could you explain why & what this does? – KidCode Jan 16 '16 at 19:38
@Richard_D make sure you remove your json configurations from your Global.ascx file (if you have any) – stoic Jun 30 '16 at 12:58

B-Lat · Answer 2 · 2015-04-23T10:22:53.457

13

Apply the [JsonIgnore] attribute to the navigation property you don't want to be serialised. It will still serialise both the parent and child entities but just avoids the self referencing loop.

edited Apr 23 '15 at 10:22

answered Feb 24 '14 at 22:17

B-Lat

1,685
1
18
25

How do you do this with DB first EF? – seebiscuit Aug 12 '16 at 17:56
As far as I'm aware it's the same. I was using DB first, so unless you're using a generator to keep regenerating your domain objects from the database, then the above should work. – B-Lat Aug 23 '16 at 09:45
That's the issue; _I am_ using a generator :( and it gets updated every once in a while when there's a schema change... I remember seeing a workaround with partials, though. – seebiscuit Aug 23 '16 at 10:17
Here is how you add attributes in a separate class that works with generated code...[https://stackoverflow.com/questions/16736494/add-data-annotations-to-a-class-generated-by-entity-framework/40666910#40666910] – Carter Medlin Aug 06 '18 at 22:55

why In web api returning an entity that has a one to many relationship causes an error?

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