[API Proposal]: System.Text.Json serialization callback context

[IdkGoodName]

Background and motivation

Newtonsoft.Json allows you to pass context to its JSON serializer via serializer settings that can later be retrieved in the callbacks. This works well enough for objects that need a specific property (like parent clients, status, etc.) to be set as passed value and it works at any depth. Unfortunately, there isn't a way to do that with System.Text.Json apart from using custom converters, that can't have serializer settings to be passed down (and you can't pass the property value to child types that require same property set if settings aren't passed). This can make it harder to move certain projects over to System.Text.Json and if not make it worse in some instances.

API Proposal

namespace System.Text.Json.Serialization
{
    public interface IJsonOnDeserialized<T>
    {
        void OnDeserialized(SomeContextType<T> context);
    }
}

or with the breaking change:

namespace System.Text.Json.Serialization
{
    public interface IJsonOnDeserialized
    {
        void OnDeserialized(StreamingContext context);
    }
}

API Usage

JsonSerializerOptions options = new JsonSerializerOptions
{
    // ...
    Context = new SomeContextType<int>(10),
    // ... 
};

public class SomeObject : IJsonOnDeserialized<int>
{
    public int Status { get; set; }
 
    public void IJsonOnDeserialized.OnDeserialized(SomeContextType<int> context) => Status = context.Value;
    
    // ... Now we can set up methods or anything else with the received context ...
}

Risks

This could lead to breaking changes if callback interfaces wouldn't use generic types.

[ghost]

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Issue Details

---

Background and motivation

Newtonsoft.Json allows you to pass context to its JSON serializer via serializer settings that can later be retrieved in the callbacks. This works well enough for objects that need a specific property (like parent clients, status, etc.) to be set as passed value and it works at any depth. Unfortunately, there isn't a way to do that with System.Text.Json apart from using custom converters, that can't have serializer settings to be passed down (and you can't pass the property value to child types that require same property set if settings aren't passed). This can make it harder to move certain projects over to System.Text.Json and if not make it worse in some instances.

API Proposal

namespace System.Text.Json.Serialization
{
    public interface IJsonOnDeserialized<T>
    {
        void OnDeserialized(SomeContextType<T> context);
    }
}

or with the breaking change:

namespace System.Text.Json.Serialization
{
    public interface IJsonOnDeserialized
    {
        void OnDeserialized(StreamingContext context);
    }
}

API Usage

JsonSerializerOptions options = new JsonSerializerOptions
{
    // ...
    Context = new SomeContextType<int>(10),
    // ... 
};

public class SomeObject : IJsonOnDeserialized<int>
{
    public int Status { get; set; }
 
    public void IJsonOnDeserialized.OnDeserialized(SomeContextType<int> context) => Status = context.Value;
    
    // ... Now we can set up methods or anything else with the received context ...
}

Risks

This could lead to breaking changes if callback interfaces wouldn't use generic types.

Author:	IdkGoodName
Assignees:	-
Labels:	api-suggestion, area-System.Text.Json, untriaged
Milestone:	-

[eiriktsarpalis]

This was discussed in the serialization callback API proposal, see #54528 (comment). I understand passing contexts was cut since it would be difficult to support in the current iteration of source generation.

cc @steveharter

[ghost]

This issue has been marked with the api-needs-work label. This may suggest that the proposal requires further refinement before it can be considered for API review. Please refer to our API review guidelines for a detailed description of the process.

When ready to submit an amended proposal, please ensure that the original post in this issue has been updated, following the API proposal template and examples as provided in the guidelines.

[eiriktsarpalis]

This would likely need to be considered in combination with #36785.

[eiriktsarpalis]

JsonSerializer doesn't support passing user state for the moment. This is something we might consider in #71718 and will be implemented in tandem with #63795. Closing as duplicate of #71718.