Making a property deserialize but not serialize with json.net

We have some configuration files which were generated by serializing C# objects with Json.net.

We'd like to migrate one property of the serialised class away from being a simple enum property into a class property.

One easy way to do this, would be to leave the old enum property on the class, and arrange for Json.net to read this property when we load the config, but not to save it again when we next serialize the object. We'll deal with generating the new class from the old enum separately.

Is there any simple way to mark (e.g. with attributes) a property of a C# object, so that Json.net will ignore it ONLY when serializing, but attend to it when deserializing?

There are actually several fairly simple approaches you can use to achieve the result you want.

Let's assume, for example, that you have your classes currently defined like this:

class Config
{
    public Fizz ObsoleteSetting { get; set; }
    public Bang ReplacementSetting { get; set; }
}

enum Fizz { Alpha, Beta, Gamma }

class Bang
{
    public string Value { get; set; }
}

And you want to do this:

string json = @"{ ""ObsoleteSetting"" : ""Gamma"" }";

// deserialize
Config config = JsonConvert.DeserializeObject<Config>(json);

// migrate
config.ReplacementSetting = 
    new Bang { Value = config.ObsoleteSetting.ToString() };

// serialize
json = JsonConvert.SerializeObject(config);
Console.WriteLine(json);

To get this:

{"ReplacementSetting":{"Value":"Gamma"}}

Approach 1: Add a ShouldSerialize method

Json.NET has the ability to conditionally serialize properties by looking for corresponding ShouldSerialize methods in the class.

To use this feature, add a boolean ShouldSerializeBlah() method to your class where Blah is replaced with the name of the property that you do not want to serialize. Make the implementation of this method always return false.

class Config
{
    public Fizz ObsoleteSetting { get; set; }

    public Bang ReplacementSetting { get; set; }

    public bool ShouldSerializeObsoleteSetting()
    {
        return false;
    }
}

Note: if you like this approach but you don't want to muddy up the public interface of your class by introducing a ShouldSerialize method, you can use an IContractResolver to do the same thing programmatically. See Conditional Property Serialization in the documentation.

Approach 2: Manipulate the JSON with JObjects

Instead of using JsonConvert.SerializeObject to do the serialization, load the config object into a JObject, then simply remove the unwanted property from the JSON before writing it out. It's just a couple of extra lines of code.

JObject jo = JObject.FromObject(config);

// remove the "ObsoleteSetting" JProperty from its parent
jo["ObsoleteSetting"].Parent.Remove();

json = jo.ToString();

Approach 3: Clever (ab)use of attributes

1. Apply a [JsonIgnore] attribute to the property that you do not want to be serialized.
2. Add an alternate, private property setter to the class with the same type as the original property. Make the implementation of that property set the original property.
3. Apply a [JsonProperty] attribute to the alternate setter, giving it the same JSON name as the original property.

Here is the revised Config class:

class Config
{
    [JsonIgnore]
    public Fizz ObsoleteSetting { get; set; }

    [JsonProperty("ObsoleteSetting")]
    private Fizz ObsoleteSettingAlternateSetter
    {
        // get is intentionally omitted here
        set { ObsoleteSetting = value; }
    }

    public Bang ReplacementSetting { get; set; }
}

For any situation where it's acceptable to have your deserialization-only property be marked internal, there's a remarkably simple solution that doesn't depend on attributes at all. Simply mark the property as internal get, but public set:

public class JsonTest {

    public string SomeProperty { internal get; set; }

}

This results in correct deserialization using default settings/resolvers/etc., but the property is stripped from serialized output.

I like sticking with attributes on this one, here is the method I use when needing to deserialize a property but not serialize it or vice versa.

STEP 1 - Create the custom attribute

public class JsonIgnoreSerializationAttribute : Attribute { }

STEP 2 - Create a custom Contract Reslover

class JsonPropertiesResolver : DefaultContractResolver
{
    protected override List<MemberInfo> GetSerializableMembers(Type objectType)
    {
        //Return properties that do NOT have the JsonIgnoreSerializationAttribute
        return objectType.GetProperties()
                         .Where(pi => !Attribute.IsDefined(pi, typeof(JsonIgnoreSerializationAttribute)))
                         .ToList<MemberInfo>();
    }
}

STEP 3 - Add attribute where serialization is not needed but deserialization is

    [JsonIgnoreSerialization]
    public string Prop1 { get; set; } //Will be skipped when serialized

    [JsonIgnoreSerialization]
    public string Prop2 { get; set; } //Also will be skipped when serialized

    public string Prop3 { get; set; } //Will not be skipped when serialized

STEP 4 - Use it

var sweet = JsonConvert.SerializeObject(myObj, new JsonSerializerSettings { ContractResolver = new JsonPropertiesResolver() });

Hope this helps! Also it's worth noting that this will also ignore the properties when Deserialization happens, when I am derserializing I just use the converter in the conventional way.

JsonConvert.DeserializeObject<MyType>(myString);

Use setter property:

[JsonProperty(nameof(IgnoreOnSerializing))]
public string IgnoreOnSerializingSetter { set { _ignoreOnSerializing = value; } }

[JsonIgnore]
private string _ignoreOnSerializing;

[JsonIgnore]
public string IgnoreOnSerializing
{
    get { return this._ignoreOnSerializing; }
    set { this._ignoreOnSerializing = value; }
}

Hope this help.

After i spent a quite long time searching how to flag a class property to be De-Serializable and NOT Serializable i found that there's no such thing to do that at all; so i came up with a solution that combines two different libraries or serialization techniques (System.Runtime.Serialization.Json & Newtonsoft.Json) and it worked for me like the following:

• flag all your class and sub-classes as "DataContract".

• flag all the properties of your class and sub-classes as "DataMember".

• flag all the properties of your class and sub-classes as "JsonProperty" except those you want them not to be serialized.

• now flag the properties the you do NOT want it to be serialized as "JsonIgnore".

• then Serialize using "Newtonsoft.Json.JsonConvert.SerializeObject" and De-Serialize using "System.Runtime.Serialization.Json.DataContractJsonSerializer".

   using System;
   using System.Collections.Generic;
   using Newtonsoft.Json;
   using System.Runtime.Serialization;
   using System.IO;
   using System.Runtime.Serialization.Json;
   using System.Text;
  
   namespace LUM_Win.model
   {
       [DataContract]
       public class User
       {
           public User() { }
           public User(String JSONObject)
           {
               MemoryStream stream = new MemoryStream(Encoding.Unicode.GetBytes(JSONObject));
               DataContractJsonSerializer dataContractJsonSerializer = new DataContractJsonSerializer(typeof(User));
  
               User user = (User)dataContractJsonSerializer.ReadObject(stream);
               this.ID = user.ID;
               this.Country = user.Country;
               this.FirstName = user.FirstName;
               this.LastName = user.LastName;
               this.Nickname = user.Nickname;
               this.PhoneNumber = user.PhoneNumber;
               this.DisplayPicture = user.DisplayPicture;
               this.IsRegistred = user.IsRegistred;
               this.IsConfirmed = user.IsConfirmed;
               this.VerificationCode = user.VerificationCode;
               this.Meetings = user.Meetings;
           }
  
           [DataMember(Name = "_id")]
           [JsonProperty(PropertyName = "_id")]
           public String ID { get; set; }
  
           [DataMember(Name = "country")]
           [JsonProperty(PropertyName = "country")]
           public String Country { get; set; }
  
           [DataMember(Name = "firstname")]
           [JsonProperty(PropertyName = "firstname")]
           public String FirstName { get; set; }
  
           [DataMember(Name = "lastname")]
           [JsonProperty(PropertyName = "lastname")]
           public String LastName { get; set; }
  
           [DataMember(Name = "nickname")]
           [JsonProperty(PropertyName = "nickname")]
           public String Nickname { get; set; }
  
           [DataMember(Name = "number")]
           [JsonProperty(PropertyName = "number")]
           public String PhoneNumber { get; set; }
  
           [DataMember(Name = "thumbnail")]
           [JsonProperty(PropertyName = "thumbnail")]
           public String DisplayPicture { get; set; }
  
           [DataMember(Name = "registered")]
           [JsonProperty(PropertyName = "registered")]
           public bool IsRegistred { get; set; }
  
           [DataMember(Name = "confirmed")]
           [JsonProperty(PropertyName = "confirmed")]
           public bool IsConfirmed { get; set; }
  
           [JsonIgnore]
           [DataMember(Name = "verification_code")]
           public String VerificationCode { get; set; }
  
           [JsonIgnore]
           [DataMember(Name = "meeting_ids")]
           public List<Meeting> Meetings { get; set; }
  
           public String toJSONString()
           {
               return JsonConvert.SerializeObject(this, new JsonSerializerSettings() { NullValueHandling = NullValueHandling.Ignore });
           }
       }
   }
  

Hope that helps ...

Depending on where in the application this takes place and if it's just one property, one manual way you can do this is by setting the property value to null and then on the model you can specify that the property be ignored if the value is null:

[JsonProperty(NullValueHandling = NullValue.Ignore)]
public string MyProperty { get; set; }

If you are working on an ASP.NET Core web app, you can globally set this for all properties in all models by setting this in your Startup.cs file:

public void ConfigureServices(IServiceCollection services) {
    // other configuration here
    services.AddMvc()
        .AddJsonOptions(options => options.SerializerSettings.NullValueHandling = NullValueHandling.Ignore);
}

with reference to @ThoHo's solution, using the setter is actually all that is needed, with no additional tags.

For me I previously had a single reference Id, that I wanted to load and add to the new collection of reference Ids. By changing the definition of the reference Id to only contain a setter method, which added the value to the new collection. Json can't write the value back if the Property doesn't have a get; method.

// Old property that I want to read from Json, but never write again. No getter.
public Guid RefId { set { RefIds.Add(value); } }

// New property that will be in use from now on. Both setter and getter.
public ICollection<Guid> RefIds { get; set; }

This class is now backwards compatible with the previous version and only saves the RefIds for the new versions.

To build upon Tho Ho's answer, this can also be used for fields.

[JsonProperty(nameof(IgnoreOnSerializing))]
public string IgnoreOnSerializingSetter { set { IgnoreOnSerializing = value; } }

[JsonIgnore]
public string IgnoreOnSerializing;

If you use JsonConvert,IgnoreDataMemberAttribute is ok.My standard library not refrence Newton.Json,and I use [IgnoreDataMember] to control object serialize.

From Newton.net help document.

>Is there any simple way to mark (e.g. with attributes) a property of a C# object, so that Json.net will ignore it ONLY when serializing, but attend to it when deserializing?

The easiest way I've found as of this writing is to include this logic in your IContractResolver.

Sample code from above link copied here for posterity:

public class Employee
{
    public string Name { get; set; }
    public Employee Manager { get; set; }

    public bool ShouldSerializeManager()
    {
        // don't serialize the Manager property if an employee is their own manager
        return (Manager != this);
    }
}

public class ShouldSerializeContractResolver : DefaultContractResolver
{
    public new static readonly ShouldSerializeContractResolver Instance = new ShouldSerializeContractResolver();

    protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)
    {
        JsonProperty property = base.CreateProperty(member, memberSerialization);

        if (property.DeclaringType == typeof(Employee) && property.PropertyName == "Manager")
        {
            property.ShouldSerialize =
                instance =>
                {
                    Employee e = (Employee)instance;
                    return e.Manager != e;
                };
        }

        return property;
    }
}

All of the answers are good but this approach seemed like the cleanest way. I actually implemented this by looking for an attribute on the property for SkipSerialize and SkipDeserialize so you can just mark up any class you control. Great question!

Jraco11's answer is very neat. In case, if you want to use the same IContractResolver both for serialization and deserialization, then you can use the following:

public class JsonPropertiesResolver : DefaultContractResolver
{
    protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)
    {
        JsonProperty property = base.CreateProperty(member, memberSerialization);

        if (member.IsDefined(typeof(JsonIgnoreSerializationAttribute)))
        {
            property.ShouldSerialize = instance => false;
        }

        return property;
    }
}

thats will do the trick, create a property with set only

example 1: https://dotnetfiddle.net/IxMXcG

[JsonProperty("disabled-protections")]
public JArray DisabledProtections { set => IsPartialResult = (value != null && value.HasValues); }

public bool IsPartialResult { get; private set; }

example 2:

private JArray _disabledProtections;

[JsonProperty("disabled-protections")]
public JArray DisabledProtections { set => _disabledProtections = value; }

public bool IsPartialResult => _disabledProtections != null && _disabledProtections.HasValues;

Use [JsonIgnore] attribute in the public property of the model class.