ASP.net webapi IHttpActionResult return complex JSON

Question

I'm battling to find a way to return complex data to my client application from the webapi server. Basically the returned list contains nested lists of another object, when I look at the response from the server I get errors as below:

An error has occurred.The 'ObjectContent`1' type failed to serialize the response body for content type 'application/json; charset=utf-8'.System.InvalidOperationExceptionAn error has occurred.Self referencing loop detected with type 'System.Data.Entity.DynamicProxies.Property_6238A3E9AD216212102B01343C0B28238D354B83E729485520A1EC884FE53A26'. Path 'propertyDataTypes[0].Properties[0].PropertyDataType.Properties'.Newtonsoft.Json.JsonSerializationException at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.CheckForCircularReference(JsonWriter writer, Object value, JsonProperty property, JsonContract contract, JsonContainerContract containerContract, JsonProperty containerProperty) at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeList(JsonWriter writer, IEnumerable values, JsonArrayContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty) at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.Serialize(JsonWriter jsonWriter, Object value, Type objectType) at Newtonsoft.Json.JsonSerializer.SerializeInternal(JsonWriter jsonWriter, Object value, Type objectType) at System.Net.Http.Formatting.BaseJsonMediaTypeFormatter.WriteToStream(Type type, Object value, Stream writeStream, Encoding effectiveEncoding) at System.Net.Http.Formatting.JsonMediaTypeFormatter.WriteToStream(Type type, Object value, Stream writeStream, Encoding effectiveEncoding) at System.Net.Http.Formatting.BaseJsonMediaTypeFormatter.WriteToStream(Type type, Object value, Stream writeStream, HttpContent content) at System.Net.Http.Formatting.BaseJsonMediaTypeFormatter.WriteToStreamAsync(Type type, Object value, Stream writeStream, HttpContent content, TransportContext transportContext, CancellationToken cancellationToken) --- End of stack trace from previous location where exception was thrown --- at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at System.Web.Http.WebHost.HttpControllerHandler.<WriteBufferedResponseContentAsync>d__1b.MoveNext()

This is my server code sending the JSON response:

    [Authorize]
    [HttpGet]
    [Route("api/propertydatatype/all")]
    public IHttpActionResult GetAllPropertyDataTypes()
    {
        var result = propertySVC.GetDataTypes().ToList();
        var config = new MapperConfiguration(cfg => {
            cfg.CreateMap<PropertyDataType, PropertyDataTypeModel>();
        });
        IMapper mapper = config.CreateMapper();
        var propertyDataTypes = mapper.Map<List<PropertyDataType>, List<PropertyDataTypeModel>>(result);
        return this.Content(HttpStatusCode.OK, new { propertyDataTypes = propertyDataTypes });
    }

The error says check for circular reference. Does PropertyDataType or PropertyDataTypeModel have properties that point to each other? — Botonomous
@Botonomous Yes they have the same properties, one is used as a ViewModel (PropertyDataTypeModel) and the (PropertyDataType) which is based on the database structure. The conversion takes place fine. — Rossco

Lukas Kolletzki Lukas Kolletzki · Accepted Answer · 2017-01-26T13:59:14

The error message indicates that your data contains a circular reference that cannot be serialized.

You can configure the behavior on circular references with something like that:

System.Web.Http.GlobalConfiguration.Configure(config =>
{
    config.Formatters.JsonFormatter.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore; 
});

You can find additional information on reference loop handling here:

ASP.net webapi IHttpActionResult return complex JSON

1 Answers