The Problem

I am creating an anonymous object in a method and assigning it properties from a class. Some of the properties can sometimes be empty (strings) and I eventually need to serialize the anonymous object to a JSON string.

When it gets serialized as JSON, I want to get rid of nulls or empty strings. I actually want to do this on a property by property basis (not generically ignoring all nulls) but it doesn't seem to be working at all!

The Code

public class Refrigerator {
    public string Brand { get; set; }
    public bool HasFood { get; set; }



    public void Serialize() {

        //ANONYMOUS OBJECT HERE
        var fridge = new {
           Brand = this.Brand; //THIS VALUE IS SOMETIMES AN EMPTY STRING!!
           HasFood = this.HasFood;
        }
        
        var value = Newtonsoft.Json.JsonConvert.SerializeObject(fridge);

        //value contains Brand as an empty string
    }

}

What I've Tried

        var fridge = new {
           Brand = this.Brand;
           HasFood = this.HasFood;

           //JsonSerializer should check this function I thought?
           ShouldSerializeBrand = new Func<bool>() {
               if(String.IsNullOrEmpty(this.Brand){
                 return false;
               }
               return true;
           }
        }

        //This should also work, but doesn't.......
        var value = Newtonsoft.Json.JsonConvert.SerializeObject(fridge, new JsonSerializerSettings 
        {
          NullValueHandling = NullValueHandling.Ignore,
          DefaultValueHandling = DefaultValueHandling.Ignore
        });

        //JSON STILL contains Brand as an empty string!!! Its still there!

Any ideas why its not working?

CodePudding user response：

One of the way for this could be that, you can use ExpandoObject for this like :

dynamic fridge = new ExpandoObject();
 if(!String.IsNullOrEmpty(this.Brand))
 {
     fridge.Brand = this.Brand;
 }
 fridge.HasFood = this.HasFood; 

This way the anonymous object will not have Brand property created unless it has a value. Now if the Brand is null of empty string, the property won't be created on the anonymous object we have created.

See this DEMO FIDDLE as example.

CodePudding user response：

An empty string i.e. the literal "" is neither a null value nor the default for a string type. As such, both options from your JsonSerializerSettings will fail to do what you want. You can solve the problem by doing what you already tried, or by creating a custom JSONConverter to add in your specific serialization logic.

Sample code based off the Newtonsoft samples:

public class FridgeJsonConverter : JsonConverter
{
 private readonly Type[] _types;

 public FridgeJsonConverter(params Type[] types)
 {
    _types = types;
 }

 public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
 {
    JToken t = JToken.FromObject(value);

    if (t.Type != JTokenType.Object)
    {
        t.WriteTo(writer);
    }
    else
    {
        JObject o = (JObject)t;
        var brandProp = o.Properties().First(x => x.Name == "Brand");
        if(brandProp.Value.ToString() == string.Empty)
         o.Remove(brandProp.Name);

        o.WriteTo(writer);
    }
 }

 public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
 {
    throw new NotImplementedException("Unnecessary because CanRead is false. The type will skip the converter.");
 }

 public override bool CanRead
 {
    get { return false; }
 }

 public override bool CanConvert(Type objectType)
 {
    return _types.Any(t => t == objectType);
 }
}

Then, in your calling code, do this:

string json = JsonConvert.SerializeObject(fridge, Formatting.Indented, new FridgeJsonConverter(typeof(Fridge)));