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Web API 2 - Implementing a PATCH

I currently have a Web API that implements a RESTFul API. The model for my API looks like this:
public class Member
{
public string FirstName { get; set; }
public string LastName { get; set; }
public DateTime Created { get; set; }
public DateTime BirthDate { get; set; }
public bool IsDeleted { get; set; }
}
I've implemented a PUT method for updating a row similar to this (for brevity, I've omitted some non-relevant stuff):
[Route("{id}")]
[HttpPut]
public async System.Threading.Tasks.Task<HttpResponseMessage> UpdateRow(int id,
[FromBody]Models.Member model)
{
// Do some error checking
// ...
// ...
var myDatabaseEntity = new BusinessLayer.Member(id);
myDatabaseEntity.FirstName = model.FirstName;
myDatabaseEntity.LastName = model.LastName;
myDatabaseEntity.Created = model.Created;
myDatabaseEntity.BirthDate = model.BirthDate;
myDatabaseEntity.IsDeleted = model.IsDeleted;
await myDatabaseEntity.SaveAsync();
}
Using PostMan, I can send the following JSON and everything works fine:
{
firstName: "Sara",
lastName: "Smith",
created: "2018/05/10",
birthDate: "1977/09/12",
isDeleted: false
}
If I send this as my body to http://localhost:8311/api/v1/Member/12 as a PUT request, the record in my data with ID of 12 gets updated to what you see in the JSON.
What I would like to do though is implement a PATCH verb where I can do partial updates. If Sara gets married, I would like to be able to send this JSON:
{
lastName: "Jones"
}
I would like to be able to send just that JSON and update JUST the LastName field and leave all the other fields alone.
I tried this:
[Route("{id}")]
[HttpPatch]
public async System.Threading.Tasks.Task<HttpResponseMessage> UpdateRow(int id,
[FromBody]Models.Member model)
{
}
My problem is that this returns all the fields in the model object (all of them are nulls except the LastName field), which makes sense since I am saying I want a Models.Member object. What I would like to know is if there is a way to detect which properties have actually been sent in the JSON request so I can update just those fields?

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

PATCH operations aren't usually defined using the same model as the POST or PUT operations exactly for that reason: How do you differentiate between a null, and a don't change. From the IETF:
With PATCH, however, the enclosed entity contains a set of
instructions describing how a resource currently residing on the
origin server should be modified to produce a new version.
You can look here for their PATCH suggestion, but sumarilly is:
[
{ "op": "test", "path": "/a/b/c", "value": "foo" },
{ "op": "remove", "path": "/a/b/c" },
{ "op": "add", "path": "/a/b/c", "value": [ "foo", "bar" ] },
{ "op": "replace", "path": "/a/b/c", "value": 42 },
{ "op": "move", "from": "/a/b/c", "path": "/a/b/d" },
{ "op": "copy", "from": "/a/b/d", "path": "/a/b/e" }
]

#Tipx's answer re using PATCH is spot on, but as you've probably already found, actually achieving that in a statically typed language like C# is a non-trivial exercise.
In the case where you're using a PATCH to represent a set of partial updates for a single domain entity (e.g. to update the first name and last name only for a contact with many more properties) you need to do something along the lines of looping each instruction in the 'PATCH' request and then applying that instruction to an instance of your class.
Applying an individual instruction will then comprise of
Finding the property of the instance that matches the name in the
instruction, or handling property names you weren't expecting
For an update: Trying to parse the value submitted in the patch into the instance property and handling the error if e.g. the instance property is a bool but the patch instruction contains a date
Deciding what to do with Add instructions as you can't add new properties to a statically typed C# class. One approach is to say that Add means "set the value of the instance's property only if property's existing value is null"
For Web API 2 on the full .NET Framework the JSONPatch github project looks to make a stab at providing this code, although it doesn't look like there's been a lot of development on that repo recently and the readme does state:
This is still very much an early project, don't use it in production
yet unless you understand the source and don't mind fixing a few bugs
;)
Things are simpler on .NET Core as that has a set of functionality to support this in the Microsoft.AspNetCore.JsonPatch namespace.
The rather useful jsonpatch.com site also lists out a few more options for Patch in .NET:
Asp.Net Core JsonPatch (Microsoft official implementation)
Ramone (a framework for consuming REST services, includes a JSON Patch implementation)
JsonPatch (Adds JSON Patch support to ASP.NET Web API)
Starcounter (In-memory Application Engine, uses JSON Patch with OT for client-server sync)
Nancy.JsonPatch (Adds JSON Patch support to NancyFX)
Manatee.Json (JSON-everything, including JSON Patch)
I need to add this functionality to an existing Web API 2 project of ours, so I'll update this answer if I find anything else that's useful while doing that.

I wanted to achieve exactly the same thing, but used a different method to others described here. I've created a working repo using this if you want to check it out:
https://github.com/emab/patch-example
If you have the following two models:
Database model
public class WeatherDBModel
{
[Key]
public int Id { get; set; }
public string City { get; set; }
public string Country { get; set; }
public double Temperature { get; set; }
public double WindSpeed { get; set; }
public double Rain { get; set; }
public Weather(int id, string city, string country, double temperature, double windSpeed, double rain)
{
Id = id;
City = city;
Country = country;
Temperature = temperature;
WindSpeed = windSpeed;
Rain = rain;
}
}
Update model
Containing exact names of database model properties. Includes properties which can be updated
public class WeatherUpdateModel
{
public string? City { get; set; }
public string? Country { get; set; }
public double Temperature { get; set; }
public double WindSpeed { get; set; }
public double Rain { get; set; }
}
This update model is sent to the service layer along with the id of the object you'd like to update.
You can then implement the following method in your repository layer which maps any non-null values from the updateModel into an existing entity if it has been found:
public Weather Update(int id, WeatherUpdate updateObject)
{
// find existing entity
var existingEntity = _context.Weather.Find(id);
// handle not found
if (existingEntity == null)
{
throw new EntityNotFoundException(id);
}
// iterate through all of the properties of the update object
// in this example it includes all properties apart from `id`
foreach (PropertyInfo prop in updateObject.GetType().GetProperties())
{
// check if the property has been set in the updateObject
// if it is null we ignore it. If you want to allow null values to be set, you could add a flag to the update object to allow specific nulls
if (prop.GetValue(updateObject) != null)
{
// if it has been set update the existing entity value
existingEntity.GetType().GetProperty(prop.Name)?.SetValue(existingEntity, prop.GetValue(updateObject));
}
}
_context.SaveChanges();
return existingEntity;
}
Using this method you can change your models without worrying about the update logic, as long as you ensure that the UpdateModel is kept up-to-date with the database model.

If a property of your object was omitted in your JSON, ASP.NET won't "set" that property on the object, the property will have its default value. In order to know which properties were sent with the JSON object you need to have a way to detect which properties of the object were set.
In order to detect which properties have "actually been sent" with the JSON object, you can modify your Member class to contain a collection of property names that were "set". Then, for all properties that you want to be able to know if they were sent in the JSON object make that when the property is set the name of the property should be added to the collection of set properties.
public class Member
{
private string _firstName;
private string _lastName;
...
private bool _isDeleted;
public string FirstName
{
get => _firstName;
set
{
_firstName = value;
_setProperties.Add(nameof(FirstName));
}
}
public string LastName
{
get => _lastName;
set
{
_lastName = value;
_setProperties.Add(nameof(LastName));
}
}
...
public bool IsDeleted
{
get => _isDeleted;
set
{
_isDeleted= value;
_setProperties.Add(nameof(IsDeleted));
}
}
private readonly HashSet<string> _setProperties = new HashSet<string>();
public HashSet<string> GetTheSetProperties()
{
return new HashSet<string>(_setProperties);
}
}
In the UpdateRow method you can now check whether a property was sent in the JSON by checking if it is in the _setProperties collection. So if you want to see if the LastName was sent in the JSON just do
bool lastNameWasInJson = model.Contains(nameof(model.LastName));

Following up to Avid Learners approach. I found this easy to add to an existing PUT method.
Alternatively to avoid loading twice you could apply update operations and then before saving apply the patch, but I'd rather load twice and have simple code.
public ResultModel Patch(UpdateModel model)
{
var record = LoadAsUpdateModel(model.Id);
if (record == null) return null;
foreach(var propertyName in model.SetProperties())
{
var property = model.GetType().GetProperty(propertyName);
property.SetValue(record, property.GetValue(model));
}
return Update(record);
}

Implementing JSON Merge Patch in ASP.NET Core WebAPI

I am interested in adding support for partial updates in my ASP.NET Core WebAPI where I only update the properties on a resource that the caller provided, leaving excluded properties unchanged.
For context, imagine I have a resource that can be described as follows:
GET /users/1
{
title: "Mister",
firstName: "Frederick",
middleName: "McFeely",
lastName: "Rodgers"
}
If I wanted to allow consumers to change the value stored in the firstName property from "Frederick" to "Fred" in isolation, I should be able to expose a PATCH endpoint that supports the JSON Merge Patch Content-Type, like so:
PATCH /users/1
Content-Type: application/merge-patch+json
{
firstName: "Fred"
}
However, I see no easy way for me to know that firstName is the only property being updated. For example, if I were to make a controller that accepted PATCH verbs, it could be scaffolded like this:
[Route("users")]
public class UsersController : Controller {
[HttpPatch("{userId:int}")]
public User Patch([FromRoute] int userId, [FromBody] User user) {
// How do I know which properties were set on User at this point?
}
}
public class User {
public String Title { get; set; }
public String FirstName { get; set; }
public String MiddleName { get; set; }
public String LastName { get; set; }
}
But I don't see how I can extract which properties' had keys defined on the JSON object before it was hydrated as a User and passed to my controller. I cannot assume a value of null to mean a property was excluded as the caller could be explicitly setting an optional property to null.
Edit
I am aware of the Microsoft.AspNetCore.JsonPatch library. This, unfortunately, expects the caller to use the "[description of changes]" to define a PATCH as described in RFC 5789, which I find unintuitive and verbose. I am referring to the "JSON Merge Patch" defined in RFC 7396.

I found a library that works: https://github.com/Morcatko/Morcatko.AspNetCore.JsonMergePatch
[HttpPatch]
[Consumes(JsonMergePatchDocument.ContentType)]
public void Patch([FromBody] JsonMergePatchDocument<Model> patch)
{
...
patch.ApplyTo(backendModel);
...
}
Or use patch.JsonPatchDocument.Operations to walk through patch request fields manually.

for simple types, I found a very simple solution using Newtonsoft.Json merge of JObjects:
public static T Patched<T>(T source, JObject patch) where T : class
{
var sourceObject = JObject.FromObject(source);
sourceObject.Merge(patch, new JsonMergeSettings() {MergeArrayHandling = MergeArrayHandling.Union});
return sourceObject.ToObject<T>();
}
public static T Patched<T>(T source, string patchCode) where T : class
{
return Patched<T>(source, JObject.Parse(patchCode));
}
Hope this helps someone searching for this topic and looking for a simple solution without external packages.

It appears like, for merge patch you will have to wait for odata support.
It is in beta at the moment and supports the merge semantics with the Delta<> class.
https://www.nuget.org/packages/Microsoft.AspNetCore.OData/

For doing a patch, you have to define PatchDocument.
More about it you can find PatchDocument
Example of method.
[HttpPatch("{userId:int}")]
public IActionResult UserPatch(int userId, [FromBody] JsonPatchDocument<User> patchDocument) {
var user = new User();
// Because it comes from url.
user.Id = userId;
patchDocument.ApplyTo(user);
// Here you call context or repository to save.
}
Example of document.
[
{ "op": "replace", "path": "/firstName", "value": "boo" },
]
That will update firstName field to 'boo' in user model.

What you might be looking for is ASP.Net Core JsonPatchDocument
https://github.com/aspnet/JsonPatch
https://learn.microsoft.com/en-us/aspnet/core/api/microsoft.aspnetcore.jsonpatch

ViewModel with dynamic elements

I need to receive the next JSON in .NET
"currentData":
{
"Name": {"system": "wfdss", "canWrite": true },
"DiscoveryDateTime": { "system": "wfdss", "canWrite": true },
"Code": { "system": "code", "canWrite": false },
...
}
This elements are dynamics, it doesn't have default elements, so, how can I define a class doing that following next model:
public class currentData
{
//TODO
//<Data Element Name>: {
//data element system: <STRING of system>,
//the last system to update data element canWrite: <Boolean>
//true if requesting system may edit data element (based on ADS), otherwise false. }, ...
public List<Property> property { get; set; }
}
public class Property
{
public string system { get; set; }
public string canWrite { get; set; }
}

If you need to post dynamic structured Json to controller i have a bad news for you - you can't map it automattically in MVC. MVC model binding mechanism work only with stronly typed collecions - you must know structure.
One of the options that i can suggest you if use FormCollection and manually get values from it:
[HttpPost]
public JsonResult JsonAction(FormCollection collection)
{
string CurrentDataNameSystem = collection["currentData.Name.system"];
// and so on...
return Json(null);
}
Another option is to pass you dynamic json as string and then manually desirialize it:
[HttpPost]
public JsonResult JsonAction(string json)
{
//You probably want to try desirialize it to many different types you can wrap it with try catch
Newtonsoft.Json.JsonConvert.DeserializeObject<YourObjectType>(jsonString);
return Json(null);
}
Anyway my point is - you shouldn't mess with dynamic json unless you really need it in MVC.
I suggest you to creage object type that contain all the passible fields but make it all nullable so you can pass your Json and it will be mapped with Model binding MVC mechanism but some fields will be null.

I think the type format you are getting is an Object with a Dictionary.
So i think you need to Deserialize your Data into this.
public class ContainerObject
{
public Dictionary<String,Property> currentData { get; set; }
}

WebAPI - Array of Objects not deserializing correctly on server side

In the client-side, I am using AngularJS and in the server-side I am using ASP.NET WebAPI.
I have two view models, ProductCriteriaViewModel and SimpleDisplayFieldViewModel:
public class ProductCriteriaViewModel
{
public int ID { get; set; }
public int? UserSearchID { get; set; }
public bool? Enabled { get; set; }
public SimpleDisplayFieldViewModel Property { get; set; }
public string Operator { get; set; }
public string CriteriaValue { get; set; }
}
public class SimpleDisplayFieldViewModel
{
public string Name { get; set; }
public string Value { get; set; }
public string PropertyType { get; set; }
}
In Angular, I submit a POST request to a WebAPI controller action with the following signature:
public IList<...> FindProducts(List<ProductCriteriaViewModel> criteriaVM, bool userFiltering)
{
...
}
In testing, I tried to send an array of Product Criterias, and checked Fiddler to see what the array looked like in the body of the POST request when it was being sent to the server. This is what the array looked like:
[
{"Enabled":true,
"Operator":"Less than",
"Property":
{"$id":"2",
"Name":"Copyright Year",
"Value":"Basic",
"PropertyType":null},
"CriteriaValue":"2013",
"IsNew":true},
{"Enabled":true,
"Operator":"Greater Than",
"Property":
{"$id":"2",
"Name":"Copyright Year",
"Value":"Basic",
"PropertyType":null},
"CriteriaValue":"1988",
"IsNew":true}
]
The above array has the correct values, however the result of deserialization on the server-side is incorrect. This is where it gets strange.
After the server deserializes the array and arrives in the controller action, the first element in criteriaVM is correct, all the values are set properly. However the second element is incorrect, CriteriaValue and Property are nulled out:
This issue only occurs whenever I choose the same search property for more than one criteria (i.e. Copyright < 2013 and Copyright > 1988). However, if I choose different properties (i.e. Copyright < 2013 and Price > 20), then all elements in the resulting criteriaVM are correctly initialized.
I do not understand what could be causing this issue. Why are only CriteriaValue and Property set to null in the second element of the List? Why does this issue only occur when I choose multiples of the same search properties?

Json.NET uses the keywords $id and $ref in order to preserve object references, so you are having troubles with your deserialization because your JSON has "$id" in the "Property" object. See this link for more information about object references.
In order to fix your deserialization issues, you can add the following line in the Register method of your WebApiConfig.cs class
config.Formatters.JsonFormatter.SerializerSettings.MetadataPropertyHandling = MetadataPropertyHandling.Ignore;
If your Web Api project does not include a WebApiConfig.cs class, simply add the configuration in your Global.asax:
GlobalConfiguration.Configuration.Formatters.JsonFormatter.SerializerSettings.MetadataPropertyHandling = MetadataPropertyHandling.Ignore;
Now your object in the web api method should look like this:

Restsharp: Deserialize json object with less/more fields than some class

I'm using Restsharp to deserialize some webservice responses, however, the problem is that sometimes this webservices sends back a json response with a few more fields. I've manage to come around this so far by adding all possible field to my matching model, but this web service will keep adding/removing fields from its response.
Eg:
Json response that works:
{
"name": "Daniel",
"age": 25
}
Matching model:
public class Person
{
public string name { get; set; }
public int age { get; set; }
}
This works fine: Person person = deserializer.Deserialize<Person>(response);
Now suppose the json response was:
{
"name": "Daniel",
"age": 25,
"birthdate": "11/10/1988"
}
See the new field bithdate? Now everything goes wrong. Is there a way to tell to restsharp to ignore those fields that are not in the model?

If there's that much variation in the fields you're getting back, perhaps the best approach is to skip the static DTOs and deserialize to a dynamic. This gist provides an example of how to do this with RestSharp by creating a custom deserializer:
// ReSharper disable CheckNamespace
namespace RestSharp.Deserializers
// ReSharper restore CheckNamespace
{
public class DynamicJsonDeserializer : IDeserializer
{
public string RootElement { get; set; }
public string Namespace { get; set; }
public string DateFormat { get; set; }
public T Deserialize<T>(RestResponse response) where T : new()
{
return JsonConvert.DeserializeObject<dynamic>(response.Content);
}
}
}
Usage:
// Override default RestSharp JSON deserializer
client = new RestClient();
client.AddHandler("application/json", new DynamicJsonDeserializer());
var response = client.Execute<dynamic>(new RestRequest("http://dummy/users/42"));
// Data returned as dynamic object!
dynamic user = response.Data.User;
A simpler alternative is to use Flurl.Http (disclaimer: I'm the author), an HTTP client lib that deserializes to dynamic by default when generic arguments are not provided:
dynamic d = await "http://api.foo.com".GetJsonAsync();
In both cases, the actual deserialization is performed by Json.NET. With RestSharp you'll need to add the package to your project (though there's a good chance you have it already); Flurl.Http has a dependency on it.