Fix deserialization of nullable string IDs (#94)

* Fix deserialization of nullable stringIDs

* Fix snapshots

Author: andrewlock

src/StronglyTypedIds/Templates/String/String_NewtonsoftJsonConverter.cs

@@ -14,6 +14,13 @@ public override void WriteJson(Newtonsoft.Json.JsonWriter writer, object value,
 
             public override object ReadJson(Newtonsoft.Json.JsonReader reader, System.Type objectType, object existingValue, Newtonsoft.Json.JsonSerializer serializer)
             {
+                if (objectType == typeof(TESTID?))
+                {
+                    var value = serializer.Deserialize<string?>(reader);
+
+                    return value is null ? null : new TESTID(value);
+                }
+
                 return new TESTID(serializer.Deserialize<string>(reader));
             }
         }

test/StronglyTypedIds.IntegrationTests/NullableStringIdTests.cs

@@ -75,6 +75,20 @@ public void CanSerializeToString_WithNewtonsoftJsonProvider()
             Assert.Equal(serializedFoo, serializedString);
         }
 
+        [Fact]
+        public void CanSerializeToNullableId_WithNewtonsoftJsonProvider()
+        {
+            var entity = new EntityWithNullableId { Id = null };
+
+            var json = NewtonsoftJsonSerializer.SerializeObject(entity);
+            var deserialize = NewtonsoftJsonSerializer.DeserializeObject<EntityWithNullableId>(json);
+
+            Assert.NotNull(deserialize);
+            // Note the different behaviour from String ID - this will _always_ deserialize to an ID
+            Assert.NotNull(deserialize.Id);
+            Assert.Null(deserialize.Id.Value.Value);
+        }
+
         [Fact]
         public void CanSerializeToString_WithSystemTextJsonProvider()
         {
@@ -407,5 +421,11 @@ public class TestEntity
             public Guid Id { get; set; }
             public EfCoreNullableStringId Name { get; set; }
         }
+        
+        
+        public class EntityWithNullableId
+        {
+            public NewtonsoftJsonNullableStringId? Id { get; set; }
+        }
     }
 }

test/StronglyTypedIds.IntegrationTests/StringIdTests.cs

@@ -81,6 +81,18 @@ public void CanSerializeToString_WithNewtonsoftJsonProvider()
             Assert.Equal(serializedFoo, serializedString);
         }
 
+        [Fact]
+        public void CanSerializeToNullableId_WithNewtonsoftJsonProvider()
+        {
+            var entity = new EntityWithNullableId { Id = null };
+
+            var json = NewtonsoftJsonSerializer.SerializeObject(entity);
+            var deserialize = NewtonsoftJsonSerializer.DeserializeObject<EntityWithNullableId>(json);
+
+            Assert.NotNull(deserialize);
+            Assert.Null(deserialize.Id);
+        }
+
         [Fact]
         public void CanSerializeToString_WithSystemTextJsonProvider()
         {
@@ -343,5 +355,10 @@ public class TestEntity
             public Guid Id { get; set; }
             public EfCoreStringId Name { get; set; }
         }
+
+        public class EntityWithNullableId
+        {
+            public NewtonsoftJsonStringId? Id { get; set; }
+        }
     }
 }

test/StronglyTypedIds.Tests/Snapshots/SourceGenerationHelperSnapshotTests.GeneratesFullIdCorrectly_type=String.verified.txt

@@ -135,6 +135,13 @@
 
             public override object ReadJson(Newtonsoft.Json.JsonReader reader, System.Type objectType, object existingValue, Newtonsoft.Json.JsonSerializer serializer)
             {
+                if (objectType == typeof(MyTestId?))
+                {
+                    var value = serializer.Deserialize<string?>(reader);
+
+                    return value is null ? null : new MyTestId(value);
+                }
+
                 return new MyTestId(serializer.Deserialize<string>(reader));
             }
         }

test/StronglyTypedIds.Tests/Snapshots/SourceGenerationHelperSnapshotTests.GeneratesIdCorrectly_type=String_c=NewtonsoftJson_i=None.verified.txt

@@ -58,6 +58,13 @@
 
             public override object ReadJson(Newtonsoft.Json.JsonReader reader, System.Type objectType, object existingValue, Newtonsoft.Json.JsonSerializer serializer)
             {
+                if (objectType == typeof(MyTestId?))
+                {
+                    var value = serializer.Deserialize<string?>(reader);
+
+                    return value is null ? null : new MyTestId(value);
+                }
+
                 return new MyTestId(serializer.Deserialize<string>(reader));
             }
         }