JsonPatch

JsonPatch is a simple library which adds JSON Patch support to .NET 6 - ASP.NET Core Minimal Web API (http://tools.ietf.org/html/rfc6902).

You can get it on NuGet here: https://www.nuget.org/packages/JsonPatch/

Usage

Step 1: Specify the Patch Document

endpoints.MapMethods("/some-resource/{id}", new[] { "PATCH" }, async (Guid id, JsonPatchDocument<SomeDto> model) =>
{
    //Remember to do some validation and all that fun stuff
    var objectToUpdate = repository.GetById(id);
    repository.Save(patchData.ApplyTo(objectToUpdate));
});

Yep - that's it. You can now use PATCH on your flash new Minimal API (https://docs.microsoft.com/en-us/aspnet/core/fundamentals/minimal-apis?view=aspnetcore-6.0)

Making a PATCH request

The main thing is to make sure the content type is "application/json-patch+json" otherwise Web API won't invoke the JsonPatch media formatter. Here's an example.

PATCH /my/data HTTP/1.1
Host: example.org
Content-Type: application/json-patch+json

[
    { "op": "add", "path": "/a/b/c", "value": "foo" }
]

Options

The path specified in the patch request can be resolved to a different property on the model using a resolver.

E.g. the ExactCasePropertyPathResolver will match a property based on an exact match

JsonPatch example:

var jsonPatchSettings = new JsonPatchSettings
{
    PathResolver = new ExactCasePropertyPathResolver(new JsonValueConverter())
};

JsonPatchCore example:

JsonPatchSettings.Options = new JsonPatchOptions
{
    PathResolver = new ExactCasePropertyPathResolver(new JsonValueConverter()),
    RequireJsonPatchContentType = false,
};

Now the request

PATCH /my/data HTTP/1.1
Host: example.org
Content-Type: application/json-patch+json

[
    { "op": "add", "path": "/sampleProperty", "value": "foo" }
]

Will be no longer be valid for the class

{
    [JsonProperty("sampleProperty")]
    public string SampeProperty {get;set;}
}

Available resolvers are

• ExactCasePropertyPathResolver
• CaseInsensitivePropertyPathResolver
• AttributePropertyPathResolver
• FlexiblePathResolver

You can add your own by extending BaseResolver and defining how to get the property from the type.

Notes

Because we are applying updates to C# objects rather than JSON objects we differ from the spec slightly, here are some points of difference.

JSON Pointer (rfc6901)

The JSON patch document uses JSON pointers to refer to properties, we don't accept paths in the following formats:

1. The path "" is invalid as it refers to the whole object, if you're replacing everything, just use PUT.
2. The path "/" is invalid as you cannot have an empty property.
3. The path "/5" is invalid as you can only update an entity, not an array of entities.

Available operations (rfc6902#section-4)

We only support a subset of available operations at this moment, add, remove, and replace.

Since C# is a typed language we have a few restrictions, hence the operations work a little differently than specified in the specification.

Here's our flavour:

1. Add will not add a property that does not exist, it can only be used to specify values on properties that are null.
2. Remove will not remove a property, it will set its value to null.
3. Replace will replace the value of a property even if it is null.