Question
Can I dynamically ignore a property from a sealed class using System.Text.Json.JsonSerializer?
Example Code
Example class from another library:
public sealed class FrozenClass
{
// [JsonIgnore] <- cannot apply because I don't own this class
public int InternalId { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
}
Default Serialization:
var person = new FrozenClass() { InternalId = 3, FirstName = "Dorothy", LastName = "Vaughan" };
var jsonString = System.Text.Json.JsonSerializer.Serialize(person);
Actual Outcome:
{ "InternalId": 3, "FirstName": "Dorothy", "LastName": "Vaughan" }
Expected Outcome:
{ "FirstName": "Dorothy", "LastName": "Vaughan" }
Alternatives that don't work
There are two other questions on how to add JsonIgnore at RunTime & add dynamic property name for serialization, but both are targeted at Newtonsoft's Json.NET - and often reference this extension method
There are several ways to modify the way a class is serialized with the native JsonSerializer, but all seem to rely on modifying the underlying class:
- You can exclude properties from serialization by adding the
[JsonIgnore]attribute to the original class - You can register a JsonConverter on a property by adding the
[JsonConverter]attribute to the original class
However, in my case, the class is from another library and cannot be extended
Workarounds
A possible workaround is to create another exportable class and setup a mapper between them
public class MyFrozenClass
{
public MyFrozenClass(FrozenClass frozen)
{
this.FirstName = frozen.FirstName;
this.LastName = frozen.LastName;
}
public string FirstName { get; set; }
public string LastName { get; set; }
}
var jsonString = System.Text.Json.JsonSerializer.Serialize(new MyFrozenClass(person));
