Web API 2 – Implementing a PATCH

Question

I hope this helps using Microsoft JsonPatchDocument:

.Net Core 2.1 Patch Action into a Controller:

[HttpPatch("{id}")]
public IActionResult Patch(int id, [FromBody]JsonPatchDocument<Node> value)
{
    try
    {
        //nodes collection is an in memory list of nodes for this example
        var result = nodes.FirstOrDefault(n => n.Id == id);
        if (result == null)
        {
            return BadRequest();
        }    
        value.ApplyTo(result, ModelState);//result gets the values from the patch request
        return NoContent();
    }
    catch (Exception ex)
    {
        return StatusCode(StatusCodes.Status500InternalServerError, ex);
    }
}

Node Model class:

[DataContract(Name ="Node")]
public class Node
{
    [DataMember(Name = "id")]
    public int Id { get; set; }

    [DataMember(Name = "node_id")]
    public int Node_id { get; set; }

    [DataMember(Name = "name")]
    public string Name { get; set; }

    [DataMember(Name = "full_name")]
    public string Full_name { get; set; }
}

A valid Patch JSon to update just the “full_name” and the “node_id” properties will be an array of operations like:

[
  { "op": "replace", "path": "full_name", "value": "NewNameWithPatch"},
  { "op": "replace", "path": "node_id", "value": 10}
]

As you can see “op” is the operation you would like to perform, the most common one is “replace” which will just set the existing value of that property for the new one, but there are others:

[
  { "op": "test", "path": "property_name", "value": "value" },
  { "op": "remove", "path": "property_name" },
  { "op": "add", "path": "property_name", "value": [ "value1", "value2" ] },
  { "op": "replace", "path": "property_name", "value": 12 },
  { "op": "move", "from": "property_name", "path": "other_property_name" },
  { "op": "copy", "from": "property_name", "path": "other_property_name" }
]

Here is an extensions method I built based on the Patch (“replace”) specification in C# using reflection that you can use to serialize any object to perform a Patch (“replace”) operation, you can also pass the desired Encoding and it will return the HttpContent (StringContent) ready to be sent to httpClient.PatchAsync(endPoint, httpContent):

public static StringContent ToPatchJsonContent(this object node, Encoding enc = null)
{
    List<PatchObject> patchObjectsCollection = new List<PatchObject>();

    foreach (var prop in node.GetType().GetProperties())
    {
        var patch = new PatchObject{ Op = "replace", Path = prop.Name , Value = prop.GetValue(node) };
        patchObjectsCollection.Add(patch);                
    }

    MemoryStream payloadStream = new MemoryStream();
    DataContractJsonSerializer serializer = new DataContractJsonSerializer(patchObjectsCollection.GetType());
    serializer.WriteObject(payloadStream, patchObjectsCollection);
    Encoding encoding = enc ?? Encoding.UTF8;
    var content = new StringContent(Encoding.UTF8.GetString(payloadStream.ToArray()), encoding, "application/json");

    return content;
}

}

Noticed that tt also uses this class I created to serialize the PatchObject using DataContractJsonSerializer:

[DataContract(Name = "PatchObject")]
class PatchObject
{
    [DataMember(Name = "op")]
    public string Op { get; set; }
    [DataMember(Name = "path")]
    public string Path { get; set; }
    [DataMember(Name = "value")]
    public object Value { get; set; }
}

A C# example of how to use the extension method and invoking the Patch request using HttpClient:

    var nodeToPatch = new { Name = "TestPatch", Private = true };//You can use anonymous type
    HttpContent content = nodeToPatch.ToPatchJsonContent();//Invoke the extension method to serialize the object

    HttpClient httpClient = new HttpClient();
    string endPoint = "https://localhost:44320/api/nodes/1";
    var response = httpClient.PatchAsync(endPoint, content).Result;

Thanks

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