Fix for issue #31, extending the use cases for removing properties via JSON patch. (#32)

* Added GitHub .NET build workflow

* Fix for Issue #31 in the original repository.

* Test for fix to Issue #31 in the original repository.

Author: mfagadar

.github/workflows/dotnetcore.yml

@@ -0,0 +1,25 @@
+name: .NET Core
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Setup .NET Core
+      uses: actions/setup-dotnet@v1
+      with:
+        dotnet-version: 3.1.101
+    - name: Install dependencies
+      run: dotnet restore
+    - name: Build
+      run: dotnet build --configuration Release --no-restore
+    - name: Test
+      run: dotnet test --no-restore --verbosity normal

src/3.0-JsonMergePatch.NewtonsoftJson/Builders/PatchBuilder.cs

@@ -23,7 +23,11 @@ public static JsonMergePatchDocument<TModel> Build<TModel>(TModel original, TMod
 			=> Build<TModel>(DiffBuilder.Build(original, patched) ?? new JObject(), options);
 
 		public static JsonMergePatchDocument<TModel> Build<TModel>(string jsonObjectPatch, JsonSerializerSettings serializerSettings = null, JsonMergePatchOptions options = null) where TModel : class
-			=> Build<TModel>(JsonConvert.DeserializeObject<JObject>(jsonObjectPatch, serializerSettings), options);
+			=> CreatePatchDocument<TModel>(
+				JsonConvert.DeserializeObject<JObject>(jsonObjectPatch, serializerSettings),
+				serializerSettings != null ? JsonSerializer.Create(serializerSettings) : defaultSerializer,
+				options ?? new JsonMergePatchOptions()
+			);
 
 		public static JsonMergePatchDocument<TModel> Build<TModel>(object jsonObjectPatch, JsonMergePatchOptions options = null) where TModel : class
 			=> Build<TModel>(JObject.FromObject(jsonObjectPatch), options);

src/3.0-JsonMergePatch.Tests/NewtonsoftJson/Patching/PropertyRemovalTest.cs

@@ -0,0 +1,54 @@
+using System.Reflection;
+using Morcatko.AspNetCore.JsonMergePatch.NewtonsoftJson.Builders;
+using Newtonsoft.Json;
+using Newtonsoft.Json.Serialization;
+using Xunit;
+
+namespace Morcatko.AspNetCore.JsonMergePatch.Tests.NewtonsoftJson.Patching {
+    public class MyClass 
+    {
+        [JsonProperty("attributes", Required = Required.DisallowNull, NullValueHandling = NullValueHandling.Ignore)]
+        public virtual MyAttributes Attributes { get; set; }
+    }
+
+    public class MyAttributes 
+    {
+        [JsonProperty("name", Required = Required.DisallowNull, NullValueHandling = NullValueHandling.Ignore)]
+        public virtual string Name { get; set; }
+    }
+
+    // see https://github.com/RicoSuter/NSwag/issues/1991#issuecomment-518600843
+    class DisallowNullContractResolver : DefaultContractResolver
+    {
+        protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)
+        {
+            var jsonProp = base.CreateProperty(member, memberSerialization);
+            if (jsonProp.Required == Required.DisallowNull)
+                jsonProp.Required = Required.AllowNull;
+            return jsonProp;
+        }
+    }    
+
+    public class PropertyRemovalTest {
+        [Fact]
+        public void PropertyRemovalWorks() {
+            var myObj = new MyClass() {
+                Attributes = new MyAttributes() {
+                    Name = "Test"
+                }
+            };
+
+            var jsonPatch = @"{
+                ""attributes"": null
+            }";
+
+            var jsonMergePatch = PatchBuilder.Build<MyClass>(
+                jsonPatch,
+                new JsonSerializerSettings() { ContractResolver = new DisallowNullContractResolver() },
+                new JsonMergePatchOptions() { EnableDelete = true });
+            jsonMergePatch.ApplyTo(myObj);
+
+            Assert.Null(myObj.Attributes);            
+        }
+    }
+}