将实体框架对象序列化为JSON

Question

public class GenericHandler : IHttpHandler
{
    public class ASSystem
    {
        public string SID { get; set; }
        public string Description { get; set; }
        public string SystemName { get; set; }
    }

    public class ErrorObj
    {
        public string ErrorMessage { get; set; }
    }

    public void ProcessRequest(HttpContext context)
    {
        HttpContext.Current.Response.ContentType = "application/json";
        HttpContext.Current.Response.ContentEncoding = Encoding.UTF8;

        string query = HttpContext.Current.Request.QueryString["SID"];


        SOFAEntities ctx = new SOFAEntities();
        JavaScriptSerializer serializer = new JavaScriptSerializer();

        try
        {
            AS_SYSTEM system = ctx.AS_SYSTEM.Where(s => s.SYSTEM_ID == query).First() as AS_SYSTEM;

            if (system != null)
            {
                ASSystem sys = new ASSystem() { SID = system.SYSTEM_ID, Description = system.DESCRIPTION, SystemName = system.SYSTEM_NAME };
                HttpContext.Current.Response.Write(serializer.Serialize(sys));
            }
        }
        catch (Exception e)
        {
            HttpContext.Current.Response.Write(serializer.Serialize(new ErrorObj() { ErrorMessage = e.Message }));
        }





    }

    public bool IsReusable
    {
        get
        {
            return false;
        }
    }
}

This works, but when i try with HttpContext.Current.Response.Write(serializer.Serialize(system)); i get the following error:

A circular reference was detected while serializing an object of type 'System.Data.Metadata.Edm.AssociationType

What i wanted was a json object representating the complete as_system object, so i dont have to map each property manually. Is there any way to solve this? Thanks!

Answer 1

If you want Serialize Entity Framework Objects into JSON, You can use JSON.NET from http://www.newtonsoft.com . to do this, install JSON.NET from nuget and use following code sample:

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

ReferenceLoopHandling.Ignore can prevent circular reference error.

Answer 2

It sounds like EF is not giving you a ASSystem , but rather some subtle dynamic subclass of that with some EF goo. If that is correct, I would argue the simplest thing to do here is to use something like AutoMapper to get a non-EF copy (into a new ASSystem() instance, untouched by EF). However, a few alternatives:

• you could try marking ASSystem as sealed , taking away EF's ability to inject itself
• you you write a custom converter and register it - this is probably more work than mapping, though

Answer 3

You can create a POCO object that can contains your data and can be serialized. For example define:

public class MySystem {
  public int SID {get; set;}
  public string Description {get; set;}
  public string SystemName {get; set;}
}

in your code use this statement:

IQuerable<MySystem> sysList = from s in ctx.AS_SYSTEM where s.SYSTEM_ID == query 
                           select new MySystem(){SID = s.SYSTEM_ID,  
                           Description = s.Description, SystemName = s.SystemName   };
MySystem sys = sysList.First();

Now you can serialize sys as in your example.

Answer 4

Try this; it works for me.

To return JSON data [in EF]:

1. Add reference System.Runtime.Serialization to the project.
2. Write code like below:

using System.Web.Script.Serialization;

    public string getValuesJson()
    {
        JavaScriptSerializer js = new JavaScriptSerializer();
        MyDBEntities ctx = new MyDBEntities();

        var myValues = (from m in ctx.TestEntity
                       where (m.id == 22)
                       select m).ToList();

        return js.Serialize(myValues);
    }

You can also check whether JSON string is valid at http://jsonlint.com/ .

Answer 5

Not sure if this will help, but try to use DataContractJsonSerializer instead of JavaScriptSerializer. As far as I know DataContractJsonSerializer is prefered over JavaScriptSerializer.