From @Mardoxx on Sunday, August 27, 2017 6:02:01 PM

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!

Support for Json Merge Patch - RFC7396 #2436

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