How to exclude property from Json Serialization

Question

I have a DTO class which I Serialize

Json.Serialize(MyClass)

How can I exclude a public property of it?

(It has to be public, as I use it in my code somewhere else)

Answer 1

If you are using Json.Net attribute [JsonIgnore] will simply ignore the field/property while serializing or deserialising.

public class Car
{
  // included in JSON
  public string Model { get; set; }
  public DateTime Year { get; set; }
  public List<string> Features { get; set; }

  // ignored
  [JsonIgnore]
  public DateTime LastModified { get; set; }
}

Or you can use DataContract and DataMember attribute to selectively serialize/deserialize properties/fields.

[DataContract]
public class Computer
{
  // included in JSON
  [DataMember]
  public string Name { get; set; }
  [DataMember]
  public decimal SalePrice { get; set; }

  // ignored
  public string Manufacture { get; set; }
  public int StockCount { get; set; }
  public decimal WholeSalePrice { get; set; }
  public DateTime NextShipmentDate { get; set; }
}

Refer http://james.newtonking.com/archive/2009/10/23/efficient-json-with-json-net-reducing-serialized-json-size for more details

Answer 2

If you are using System.Web.Script.Serialization in the .NET framework you can put a ScriptIgnore attribute on the members that shouldn't be serialized. See the example taken from here:

Consider the following (simplified) case:

public class User {
    public int Id { get; set; }
    public string Name { get; set; }
    [ScriptIgnore]
    public bool IsComplete
    {
        get { return Id > 0 && !string.IsNullOrEmpty(Name); }
    } 
} 

In this case, only the Id and the Name properties will be serialized, thus the resulting JSON object would look like this:

{ Id: 3, Name: 'Test User' }

PS. Don't forget to add a reference to "System.Web.Extensions" for this to work

Answer 3

EDIT 2023-06-29: updated answer and added info about .NET core and System.Text.Json

---

If you don't want to decorate properties with some attributes, or if you have no access to the class, or if you want to decide what to serialize during runtime, here's how you do it:

1. In Newtonsoft.Json

Newtonsoft solution is pretty simple:

//short helper class to ignore some properties from serialization
public class IgnorePropertiesResolver : DefaultContractResolver
{
    private readonly HashSet<string> ignoreProps;
    public IgnorePropertiesResolver(IEnumerable<string> propNamesToIgnore)
    {
        this.ignoreProps = new HashSet<string>(propNamesToIgnore);
    }

    protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)
    {
        JsonProperty property = base.CreateProperty(member, memberSerialization);
        if (this.ignoreProps.Contains(property.PropertyName))
        {
            property.ShouldSerialize = _ => false;
        }
        return property;
    }
}

Usage

JsonConvert.SerializeObject(YourObject, new JsonSerializerSettings()
        { ContractResolver = new IgnorePropertiesResolver(new[] { "Prop1", "Prop2" }) });

Make sure you cache the ContractResolver object if you decide to use this answer, otherwise performance may suffer.

I've published the code here in case anyone wants to add anything: https://github.com/jitbit/JsonIgnoreProps

2. In System.Text.Json

.NET core uses System.Text.Json by default, it's faster, but you don't have all the flexibility of Newtonsoft. However here some solutions for excluding properties at runtime:

1. In .NET 7 and above you can control which properties get serialized like described here: https://devblogs.microsoft.com/dotnet/system-text-json-in-dotnet-7/#example-conditional-serialization

2. In .NET 6 (and below) - you can cast to an interface (which I personally find the cleanest) or use a mapper. Both options are descibed in this answer https://stackoverflow.com/a/61344654/56621

Answer 4

You can use [ScriptIgnore]:

public class User
{
    public int Id { get; set; }
    public string Name { get; set; }
    [ScriptIgnore]
    public bool IsComplete
    {
        get { return Id > 0 && !string.IsNullOrEmpty(Name); }
    }
}

In this case the Id and then name will only be serialized

Answer 5

If you are not so keen on having to decorate code with Attributes as I am, esp when you cant tell at compile time what will happen here is my solution.

Using the Javascript Serializer

public static class JsonSerializerExtensions
{
    public static string ToJsonString(this object target,bool ignoreNulls = true)
    {
        var javaScriptSerializer = new JavaScriptSerializer();
        if(ignoreNulls)
        {
            javaScriptSerializer.RegisterConverters(new[] { new PropertyExclusionConverter(target.GetType(), true) });
        }

        return javaScriptSerializer.Serialize(target);
    }
        
    public static string ToJsonString(this object target, Dictionary<Type, List<string>> ignore, bool ignoreNulls = true)
    {
        var javaScriptSerializer = new JavaScriptSerializer();
        foreach (var key in ignore.Keys)
        {
            javaScriptSerializer.RegisterConverters(new[] { new PropertyExclusionConverter(key, ignore[key], ignoreNulls) });
        }
        return javaScriptSerializer.Serialize(target);
    }
 }
    
    
public class PropertyExclusionConverter : JavaScriptConverter
{
    private readonly List<string> propertiesToIgnore;
    private readonly Type type;
    private readonly bool ignoreNulls;
    
    public PropertyExclusionConverter(Type type, List<string> propertiesToIgnore, bool ignoreNulls)
    {
        this.ignoreNulls = ignoreNulls;
        this.type = type;
        this.propertiesToIgnore = propertiesToIgnore ?? new List<string>();
    }
    
    public PropertyExclusionConverter(Type type, bool ignoreNulls)
        : this(type, null, ignoreNulls){}
    
    public override IEnumerable<Type> SupportedTypes
    {
        get { return new ReadOnlyCollection<Type>(new List<Type>(new[] { this.type })); }
    }
    
    public override IDictionary<string, object> Serialize(object obj, JavaScriptSerializer serializer)
    {
       var result = new Dictionary<string, object>();
       if (obj == null)
       {
           return result;
       }
       var properties = obj.GetType().GetProperties();
       foreach (var propertyInfo in properties)
       {
           if (!this.propertiesToIgnore.Contains(propertyInfo.Name))
           {
               if(this.ignoreNulls && propertyInfo.GetValue(obj, null) == null)
               {
                     continue;
               }
               result.Add(propertyInfo.Name, propertyInfo.GetValue(obj, null));
           }
        }
        return result;
    }
    
    public override object Deserialize(IDictionary<string, object> dictionary, Type type, JavaScriptSerializer serializer)
    {
        throw new NotImplementedException(); //Converter is currently only used for ignoring properties on serialization
    }
}

Answer 6

If you are using System.Text.Json then you can use [JsonIgnore].
FQ: System.Text.Json.Serialization.JsonIgnoreAttribute

Official Microsoft Docs: JsonIgnoreAttribute

As stated here:

The library is built-in as part of the .NET Core 3.0 shared framework.
For other target frameworks, install the System.Text.Json NuGet package. The package supports:

• .NET Standard 2.0 and later versions
• .NET Framework 4.6.1 and later versions
• .NET Core 2.0, 2.1, and 2.2

Answer 7

For C# 9's records it's [property: JsonIgnore]

using System.Text.Json.Serialization;

public record R(
   string Text2
   [property: JsonIgnore] string Text2)

For the classic style it's still just [JsonIgnore].

using System.Text.Json.Serialization;

public record R
{
   public string Text {get; init; }

   [JsonIgnore] 
   public string Text2 { get; init; }
}

Answer 8

You can also use the [NonSerialized] attribute

[Serializable]
public struct MySerializableStruct
{
    [NonSerialized]
    public string hiddenField;
    public string normalField;
}

From the MS docs:

Indicates that a field of a serializable class should not be serialized. This class cannot be inherited.

---

If you're using Unity for example (this isn't only for Unity) then this works with UnityEngine.JsonUtility

using UnityEngine;

MySerializableStruct mss = new MySerializableStruct 
{ 
    hiddenField = "foo", 
    normalField = "bar" 
};
Debug.Log(JsonUtility.ToJson(mss)); // result: {"normalField":"bar"}

Answer 9

Add System.Text.Json Version for dotnet core

For compile time, add [JsonIgnore] as suggested in the above answer.

For run time, JsonConverter needs to be added into the options.

First, create a JsonConverter for the type you want to exclude, for example ICollection<LabMethod> below

public class LabMethodConverter : JsonConverter<ICollection<LabMethod>>
{
    public override ICollection<LabMethod> Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        //deserialize JSON into a ICollection<LabMethod>
        return null;
    }

    public override void Write(Utf8JsonWriter writer, ICollection<LabMethod> value, JsonSerializerOptions options)
    {
        //serialize a ICollection<LabMethod> object
        writer.WriteNullValue();
    }
}

Then add to options when you serialize Json

var options = new JsonSerializerOptions();
options.Converters.Add(new LabMethodConverter());
var new_obj = Json(new { rows = slice, total = count }, options);