How to sort properties alphabetically when serializing JSON using Netwonsoft library?

Question

When serializing objects using the Netwonsoft.JSON library, it's possible to specify the output order using JsonPropertyAttribute property Order. However, I would like to also sort alphabetically the properties by default on top of that.

Answer 1

You can create a custom contract resolver, by extending Newtonsoft.Json.Serialization.DefaultContractResolver. The CreateProperties method is the one responsible of the property order, so overriding it, and re-sorting the properties would change the behaviour in the way you want:

public class OrderedContractResolver : Newtonsoft.Json.Serialization.DefaultContractResolver
{
    protected override System.Collections.Generic.IList<Newtonsoft.Json.Serialization.JsonProperty> CreateProperties(System.Type type, Newtonsoft.Json.MemberSerialization memberSerialization)
    {
        var @base = base.CreateProperties(type, memberSerialization);
        var ordered = @base
            .OrderBy(p => p.Order ?? int.MaxValue)
            .ThenBy(p => p.PropertyName)
            .ToList();
        return ordered;
    }
}

In order to use a custom contract resolver you have to create a custom Newtonsoft.Json.JsonSerializerSettings and set its ContractResolver to an instance of it:

var jsonSerializerSettings = new Newtonsoft.Json.JsonSerializerSettings
{
    ContractResolver = new OrderedContractResolver(),
};

and then serialize using the above settings object's instance:

using (Newtonsoft.Json.JsonWriter writer = new Newtonsoft.Json.JsonTextWriter(sw))
{
    var serializer = Newtonsoft.Json.JsonSerializer.Create(jsonSerializerSettings);
    serializer.Serialize(writer, jsonObject);
}

where sw is a simple string writer:

var sb = new System.Text.StringBuilder();
var sw = new System.IO.StringWriter(sb);

and jsonObject is the object you wish to serialize.