Question 290769 in Json Question posted in
Our archive of expertly curated questions and answers provides insights and solutions to common problems related to this popular data interchange format. From parsing and manipulating JSON data to integrating it with various programming languages and web services, our archive has got you covered. Start exploring today and take your JSON skills to the next level

How to ignore Property on JSON deserialization?

My Dto has Id property:

  public class ADto
  {
      public int Id { get; set; }
      public string Text { get; set; }
  }

The Id is set by EF Core not by Frontend request, so I want to ignore it on deserialization ( but do not ignore on serialization, so already set Id by EF Core will be returned to Frontend), how to achieve that with attributes? I am using using System.Text.Json.Serialization;.

Tags:

3

Answers


  1. 0

    You can use the JsonIgnore attribute from System.Text.Json.Serialization. This attribute allows you to specify that a property should be ignored during the deserialization process but included during serialization.

    public class ADto
{
    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
    public int Id { get; set; }

    public string Text { get; set; }
}
    Login or Signup to reply.
  2. 0

    There is no way to achieve exactly what you want with the attributes built in to System.Text.Json as of .NET 8 or earlier.

    As a workaround, in .NET 7 and later you could create a custom attribute, then check for it in a custom typeInfo modifier when generating contracts for your types.

    First define the following attribute:

    [System.AttributeUsage(AttributeTargets.Property | AttributeTargets.Field, Inherited = true)]
public sealed class JsonIgnoreOnDeserializationAttribute : System.Text.Json.Serialization.JsonAttribute
{
    public static void Apply(JsonTypeInfo typeInfo)
    {
        if (typeInfo.Kind != JsonTypeInfoKind.Object)
            return;
        foreach (var property in typeInfo.Properties)
        {
            if (property.AttributeProvider?.IsDefined(typeof(JsonIgnoreOnDeserializationAttribute), true) == true)
                property.Set = null;
        }
    }
}

    And modify your type as follows:

    public class ADto
{
    [JsonIgnoreOnDeserialization]
    public int Id { get; set; }
    public string Text { get; set; }
}

    Then, when setting up your serialization options, apply the modifier in .NET 8 by calling WithAddedModifier() like so:

    var options = new JsonSerializerOptions
{
    // If you are using source generation, use SourceGenerationContext.Default here instead.
    TypeInfoResolver = new DefaultJsonTypeInfoResolver() 
        .WithAddedModifier(JsonIgnoreOnDeserializationAttribute.Apply),
    // Add other options as required, e.g.:
    WriteIndented = true,
};

    Demo fiddle #1 here.

    Notes:

    • The extension method WithAddedModifier() is new in .NET 8 and allows for modification of contracts of arbitrary IJsonTypeInfoResolver instances, including both both DefaultJsonTypeInfoResolver and JsonSerializerContext.

      In .NET 7, use DefaultJsonTypeInfoResolver and set the modifier explicitly:

      var options = new JsonSerializerOptions
{
    TypeInfoResolver = new DefaultJsonTypeInfoResolver() 
    {
        Modifiers = { JsonIgnoreOnDeserializationAttribute.Apply },
    },
    // Add other options as required, e.g.:
    WriteIndented = true,
};

      Demo fiddle #2 here.

    • .NET 8 also has the ability to serialize properties that are entirely nonpublic, so you could consider modifying ADto by marking Id with [JsonIgnore] and adding a private get-only surrogate property like so:

      public class ADto
{
    public ADto() { }

    [JsonInclude, JsonPropertyName("Id")]
    private int DeserializedId => Id;

    [JsonIgnore]
    public int Id { get; set; }
    public string Text { get; set; }
}

      In .NET 7 and earlier the surrogate property would need to be public, which you probably would not want.

      Demo fiddle #3 here.

    Login or Signup to reply.
  3. 0

    How about this approach, without attributes, simple and clear:

    var id = myDto.Id;  // Save the Id
myDto = JsonSerializer.Deserialize<aDto>(json);
myDto.Id = id;      // Restore the Id
    Login or Signup to reply.
Please signup or login to give your own answer.

Back To Top
Search