WCF restful returning JSON by using Entity Framework Complex

Question

recently I have set up a WCF restful service with EF4. It all worked out when returning XML format response. however when it comes to JSON, I got 504 Error. unable to return json data, WCF Resful Service .NET 4.0

By digging deeper by using Service Trace Viewer: I found this error:

'The type 'xxx.DataEntity.AppView' cannot be serialized to JSON because its IsReference setting is 'True'. The JSON format does not support references because there is no standardized format for representing references. To enable serialization, disable the IsReference setting on the type or an appropriate parent class of the type.'

The "AppView" is a complex object class which generated by EF4 from a store procedure. I spend quite a bit time google how to disable the IsReference, very little result so far.

anyone? with any solutions?

thanks in advance

Code:

[OperationContract]
        [WebInvoke(Method = "GET",
            BodyStyle = WebMessageBodyStyle.Wrapped,
            UriTemplate = "App/{id}/{format}")]
        AppView FuncDetail(string id, string format);



public AppView FuncDetail(string id, string format)
        {
            SetResponseFormat(format);
            return AppSvcs.GetById(id);
        }


private void SetResponseFormat(string format)
            {
                if (format.ToLower() == "json")
                {
                    ResponseContext.Format = WebMessageFormat.Json;
                }
                else
                {
                    ResponseContext.Format = WebMessageFormat.Xml;
                }
            }

score 1 · Answer 1 · answered Jan 19 '11 at 21:14

I was running into the same problem, as caused by using the auto-generated ADO Entity Models. I have not found a direct fix for this issue, but as a work around, I serialize the response as json explicitly.

So in your example, the AppView FuncDetail looks like this:

public object FuncDetail(string id, string format)
    {
        SetResponseFormat(format);

        // where AppSvc is the object type and the enumerable list of this type is returned by the GetById method, cast it to a json string
        return JSONSerializer.ToJson<AppSvc>(AppSvcs.GetById(id));
    }

Here are the Serializers that I'm using:

public static class GenericSerializer 
{
public static DataTable ToDataTable<T>(IEnumerable<T> varlist)
{
    DataTable dtReturn = new DataTable();

    // column names 
    PropertyInfo[] oProps = null;

    if (varlist == null) return dtReturn;

    foreach (T rec in varlist)
    {
        // Use reflection to get property names, to create table, Only first time, others will follow 
        if (oProps == null)
        {
            oProps = ((Type)rec.GetType()).GetProperties();
            foreach (PropertyInfo pi in oProps)
            {
                Type colType = pi.PropertyType;

                if ((colType.IsGenericType) && (colType.GetGenericTypeDefinition()
                == typeof(Nullable<>)))
                {
                    colType = colType.GetGenericArguments()[0];
                }

                dtReturn.Columns.Add(new DataColumn(pi.Name, colType));
            }
        }

        DataRow dr = dtReturn.NewRow();

        foreach (PropertyInfo pi in oProps)
        {
            dr[pi.Name] = pi.GetValue(rec, null) == null ? DBNull.Value : pi.GetValue
            (rec, null);
        }

        dtReturn.Rows.Add(dr);
    }
    return dtReturn;
}

}

public static class JSONSerializer 
{
public static string ToJson<T>(IEnumerable<T> varlist)
{
    DataTable dtReturn = GenericSerializer.ToDataTable(varlist);
    return GetJSONString(dtReturn);
}

    static object RowsToDictionary(this DataTable table)
{

    var columns = table.Columns.Cast<DataColumn>().ToArray();

    return table.Rows.Cast<DataRow>().Select(r => columns.ToDictionary(c => c.ColumnName, c => r[c]));

}

static Dictionary<string, object> ToDictionary(this DataTable table)
{

    return new Dictionary<string, object>
    {
        { table.TableName, table.RowsToDictionary() }
    };

}

static Dictionary<string, object> ToDictionary(this DataSet data)
{

    return data.Tables.Cast<DataTable>().ToDictionary(t => "Table", t => t.RowsToDictionary());

}

public static string GetJSONString(DataTable table)
{

    JavaScriptSerializer serializer = new JavaScriptSerializer();

    return serializer.Serialize(table.ToDictionary());

}

public static string GetJSONString(DataSet data)
{

    JavaScriptSerializer serializer = new JavaScriptSerializer();

    return serializer.Serialize(data.ToDictionary());

}}

score 1 · Answer 2 · answered Apr 26 '11 at 19:44

1

It is a lot clearer to use Entity Metadata instead of Reflection. The Metadata is pretty extensive.

answered Apr 26 '11 at 19:44

Uajal

11
1

score 1 · Accepted Answer · answered Jan 28 '12 at 21:40

I ran into exactly the same issue. It only happened on one of my service methods where I was trying to return JSON serialised Entity objects. For all my other methods I was returning JSON serialised data transfer objects (DTOs), which are stand-alone and not connected to the Entity framework. I am using DTOs for data posted into methods. Often, the data you send out does not need all the data you store in the model or the database e.g. ID values, updated dates, etc. The mapping is done in the model class, like so:

public partial class Location
{

    public static LocationDto CreateLocationDto(Location location)
    {
        LocationDto dto = new LocationDto
        {
            Accuracy = location.Accuracy,
            Altitude = location.Altitude,
            Bearing = location.Bearing                
        };
        return dto;
    }

It may seem a bit clunky but it works and it ensures that you only send the data fields you intended to send back. It works for me because I only have 5 or 6 entities but I can see that it would get a bit tedious if you have lots of classes.

score 0 · Answer 4 · answered Jan 03 '13 at 20:50

another way to do this is to use LINQ to create an anonymous type with the subset of fields that you need from your entity and then use JSON.NET to serialize the collection of anon types that you created in the LINQ statement. then persist that collection out as a string by serializing.

WCF restful returning JSON by using Entity Framework Complex

4 Answers4