Can JavaScriptSerializer exclude properties with null/default values?

Question

I'm using JavaScriptSerializer to serialize some entity objects.

The problem is, many of the public properties contain null or default values. Is there any way to make JavaScriptSerializer exclude properties with null or default values?

I would like the resulting JSON to be less verbose.

Answer 1

FYI, if you'd like to go with the easier solution, here's what I used to accomplish this using a JavaScriptConverter implementation with the JavaScriptSerializer:

private class NullPropertiesConverter: JavaScriptConverter {
 public override object Deserialize(IDictionary<string, object> dictionary, Type type, JavaScriptSerializer serializer) {
  throw new NotImplementedException();
 }

 public override IDictionary<string, object> Serialize(object obj, JavaScriptSerializer serializer) {
  var jsonExample = new Dictionary<string, object >();
  foreach(var prop in obj.GetType().GetProperties()) {
   //check if decorated with ScriptIgnore attribute
   bool ignoreProp = prop.IsDefined(typeof(ScriptIgnoreAttribute), true);

   var value = prop.GetValue(obj, BindingFlags.Public, null, null, null);
   if (value != null && !ignoreProp)
    jsonExample.Add(prop.Name, value);
  }

  return jsonExample;
 }

 public override IEnumerable<Type> SupportedTypes {
  get {
   return GetType().Assembly.GetTypes();
  }
 }
}

and then to use it:

var serializer = new JavaScriptSerializer();
serializer.RegisterConverters(new JavaScriptConverter[] {
  new NullPropertiesConverter()
});
return serializer.Serialize(someObjectToSerialize);

Answer 2

The solution that worked for me:

The serialized class and properties would be decorated as follows:

[DataContract]
public class MyDataClass
{
  [DataMember(Name = "LabelInJson", IsRequired = false)]
  public string MyProperty { get; set; }
}

IsRequired was the key item.

The actual serialization could be done using DataContractJsonSerializer:

public static string Serialize<T>(T obj)
{
  string returnVal = "";
  try
  {
    DataContractJsonSerializer serializer = new DataContractJsonSerializer(obj.GetType());
    using (MemoryStream ms = new MemoryStream())
    {
      serializer.WriteObject(ms, obj);
      returnVal = Encoding.Default.GetString(ms.ToArray());
    }
  }
  catch (Exception /*exception*/)
  {
    returnVal = "";
    //log error
  }
  return returnVal;
}

Answer 3

For the benefit of those who find this on google, note that nulls can be skipped natively during serialization with Newtonsoft.Json

var json = JsonConvert.SerializeObject(
            objectToSerialize,
            new JsonSerializerSettings {NullValueHandling = NullValueHandling.Ignore});

Answer 4

You can implement a JavaScriptConverter and register it using the RegisterConverters method of JavaScriptSerializer.

Answer 5

Json.NET has options to automatically exclude null or default values.

Answer 6

This code is block null and default(0) values for numeric types

private class NullPropertiesConverter: JavaScriptConverter {
 public override object Deserialize(IDictionary < string, object > dictionary, Type type, JavaScriptSerializer serializer) {
  throw new NotImplementedException();
 }

 public override IDictionary < string, object > Serialize(object obj, JavaScriptSerializer serializer) {
  var jsonExample = new Dictionary < string,
   object > ();
  foreach(var prop in obj.GetType().GetProperties()) {
   //this object is nullable 
   var nullableobj = prop.PropertyType.IsGenericType && prop.PropertyType.GetGenericTypeDefinition() == typeof(Nullable < > );
   //check if decorated with ScriptIgnore attribute
   bool ignoreProp = prop.IsDefined(typeof(ScriptIgnoreAttribute), true);

   var value = prop.GetValue(obj, System.Reflection.BindingFlags.Public, null, null, null);
   int i;
   //Object is not nullable and value=0 , it is a default value for numeric types 
   if (!(nullableobj == false && value != null && (int.TryParse(value.ToString(), out i) ? i : 1) == 0) && value != null && !ignoreProp)
    jsonExample.Add(prop.Name, value);
  }

  return jsonExample;
 }

 public override IEnumerable < Type > SupportedTypes {
  get {
   return GetType().Assembly.GetTypes();
  }
 }
}

Answer 7

Rather than doing tricky things to the System.Web.Script.Serialization settings in a legacy project, breaking God-knows what else, I simply added a derived class to include/exclude fields as needed.

Pseudo-code:

public class MyBaseClass
{
    public string MyRequiredField { get; set; }
}

public class MyDerivedClass : MyBaseClass
{
    public string MyOptionalField { get; set; }
}

public class MyFactory
{
    public System.Web.Script.Serialization.JavaScriptSerializer serializer { get; set; }

    public GetJsonArray(MyBaseClass[] thingsToSerialize)
    {
        return serializer.Serialize(thingsToSerialize);
    }
}

And the thingsToSerialize array can have objects of both MyBaseClass and MyDerivedClass. This won't handle every scenario super elegantly - if you need a better, longer lasting solution, use the latest .NET version with System.Text.Json.JsonSerializer

Answer 8

Without changing toe DataContractSerializer

You can use ScriptIgnoreAttribute

[1] http://msdn.microsoft.com/en-us/library/system.web.script.serialization.scriptignoreattribute.aspx