Support for Json Merge Patch - RFC7396

[adnan-kamili]

Hi,

Are their any plans to support the Json Merge Patch

https://tools.ietf.org/html/rfc7396

[vhe1]

Seconded.
Can we have support for it?
It's much easier on the frontend developers and the rfc 6902 patch has a gaping security hole in that any path expression can be added to the list, regardless of whether the property exists on the type given in the generic type parameter.

[gilmishal]

Third.
RFC 6902 is also not very client side friendly.

[Mardoxx]

This would be great. Seems a lot more appropriate for what I'd imagine the "average" user requires of JSON Patch.

[Mardoxx]

What does the 1 - Ready label mean?

Has an API for this already been decided? Or is it in discussion -- if so is this public?

I have been playing around a bit and I've got a working PoC which allows for uhhh.. this:

// Normal DTO/model
public class PersonDetailsUpdate
{
    public string GivenName { get; set; }
    public string Surname { get; set; }
    public int Age { get; set; }
    public int? GroupId { get; set; }
}

[HttpPatch("Users/{id:int}")]
public IActionResult Patch([FromRoute]int id, JsonMergeDocument<PersonDetailsUpdate> mergeDocument)
{
    JsonMergeDocumentMember<int?> groupIdMember = mergeDocument.Member(x => x.GroupId);
    if (groupIdMember.IsSet)
    {
        int? newGroupId = groupIdMember.Value;
        if (newGroupId.HasValue) {
            // Throw if group is not valid
            _groupsService.SetUserGroup(id, newGroupId);
        }
        
        _groupsService.UnSetUserGroup(id);
    }

    using (UsersDbContext usersContext = new UsersDbContext())
    {
        // Check if user exists
        UserEntity user = new UserEntity
        {
            Id = id
        };

        EntityEntry entity = dbContext.Users.Attach(dbUser);

        foreach(IEnumerable<JsonMergeDocumentMember> member in mergeDocument.Members.Where(x => x.IsSet))
        {
            PropertyEntry entityProp = entity.Member(member.Name) as PropertyEntry;
            if (entityProp != null)
            {
                 if (entityProp.MetaData.ClrType != member.Type)
                 {
                     // perhaps try convert type and set
                 }
                entityProp.CurrentValue = member.Value;
            }              
        }

        usersContext.SaveChanges();
    }

    return NoContent();
}

Assume the following data is persisted:

UserEntity {
  Id = 10,
  FirstName = "Mardoxx",
  Surname = "",
  Age = 99
}

UserGroup {
    UserId = 10,
    GroupId = 100
}

With group information being stored in a completely isolated service.

That is, a GET Users/10 would return:

{
    "UserId": 10,
    "FirstName": "Mardoxx",
    "Surname": "",
    "Age": 99,
    "GroupId" : 100
}

Sending PATCH Users/10 with a body of

{
    "Age": 20,
    "GroupId" : null
}

Will update the user's age to 20, and remove the user from its group, i.e. GroupId to null.

A GET Users/10 now returns:

{
    "UserId": 10,
    "FirstName": "Mardoxx",
    "Surname": "",
    "Age": 20,
    "GroupId" : null
}

JsonMergeDocumentMember and JsonMergeDocumentMember<T> are DataContractSerializable.

JsonMergePatch<T> is as well.

---

This is the sort of functionality I would like from an official impl of Json Merge Patch. Validation is a necessary addition to this, so is an T ApplyTo<T>(T to) function. Could also perhaps do with a object ToObject() which emits a new anonymous type with the fields defined -- probably out of scope of this though. Can definitely be improved upon. Also not sure how it copes with complex objects (e.g. Post with an Author field, although I think that is automatically handled by the deserialisation). From the spec it seems that only first-level properties can be patched. You can't do a partial update to a nested field (which works out quite nicely actually)

An official solution to something like this would be really desirable!

[peabnuts123]

Just pitching in from a front-end-dev perspective. Granted that JSON Patch is a nice standard but it's pretty widely accepted to do operations in a JSON-Merge kind of way. To a JS developer, it would be pretty weird if their backend developer told them they couldn't support this kind of operation, it would be generally seen as basically an incapable/not very useful technology.

[Mardoxx]

Ok so I've cleaned it up a bit, API is a little different now, Members is a Dictionary<string JsonMergePatchValue>
For the end user all they need to do is change their controller object types to be JsonMergePatchDocument<>, and then use T patchDoc.ApplyTo<TObj>(TObj object) or whatever to update an object for example, or do what I did above.
I've basically designed it in a way that I want it to work. I really want to get the ball rolling with this because I feel it would be very useful!

Shall I write a few tests and do a PR? Or has work on this already begun?

I want this to be DataContract serializable too as it would be great to be able to send this object around in Service Fabric using their remoting libs, for which this is a requirement. Not quite sure how to achieve this though.

[mhosman]

+1 For this. Please add support for Json Merge Patch!

[rynowak]

@Mardoxx - we'll discuss and get back to you next week. We're still planning the set of features we're going to do for 2.1, and this is under consideration. I'm putting a reminder on my calendar right now.

If you have an example of this somewhere in a repo that we can look at that would help.

[tinchoel10]

+1 Please add json merge patch, this is more client-friendly, easier to understand and to manage in a lot of situations. Is a very important feature.

[Mardoxx]

@rynowak Amazing thanks.

Done here - https://github.com/Mardoxx/RJBM.JsonMergePatch Cleaned it up a lot and simplified it... a lot. Hacked together a handful of tests that should give an idea of behaviour. Not happy about a few things, see here, but happy enough about general API for it (not necessarily the names of things though!). Gives a basic idea of what I want.

Can add end to end example if you like?

[mhosman]

Hey @Mardoxx, this is a working (non-official) example? I know there are several things to work in it (Mardoxx/RJBM.JsonMergePatch#1), but it works?

[Mardoxx]

@mhosman Yeah it works! Very very basic example here or slight modifications to above should work 😄