fix(*): allow null data objects

Issue #21 - 2

Author: jaredcnance

src/JsonApiDotNetCore/Builders/DocumentBuilder.cs

@@ -132,7 +132,9 @@ private void _addRelationships(DocumentData data, ContextEntity contextEntity, I
                     var navigationEntity = _jsonApiContext.ContextGraph
                         .GetRelationship(entity, r.RelationshipName);
 
-                    if (navigationEntity is IEnumerable)
+                    if(navigationEntity == null)
+                        relationshipData.SingleData = null;
+                    else if (navigationEntity is IEnumerable)
                         relationshipData.ManyData = _getRelationships((IEnumerable<object>)navigationEntity, r.RelationshipName);
                     else
                         relationshipData.SingleData = _getRelationship(navigationEntity, r.RelationshipName);
@@ -164,6 +166,8 @@ private List<DocumentData> _getIncludedEntities(ContextEntity contextEntity, IId
 
         private DocumentData _getIncludedEntity(IIdentifiable entity)
         {
+            if(entity == null) return null;
+            
             var contextEntity = _jsonApiContext.ContextGraph.GetContextEntity(entity.GetType());
 
             var data = new DocumentData

src/JsonApiDotNetCore/Controllers/JsonApiController.cs

@@ -1,3 +1,4 @@
+using System.Collections;
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading.Tasks;
@@ -126,9 +127,6 @@ public virtual async Task<IActionResult> GetRelationshipAsync(TId id, string rel
             var relationship = _jsonApiContext.ContextGraph
                 .GetRelationship<T>(entity, relationshipName);
 
-            if (relationship == null)
-                return NotFound();
-
             return Ok(relationship);
         }
 

src/JsonApiDotNetCore/Formatters/JsonApiOutputFormatter.cs

@@ -2,6 +2,7 @@
 using System.Text;
 using System.Threading.Tasks;
 using JsonApiDotNetCore.Internal;
+using JsonApiDotNetCore.Models;
 using JsonApiDotNetCore.Serialization;
 using JsonApiDotNetCore.Services;
 using Microsoft.AspNetCore.Mvc.Formatters;
@@ -65,23 +66,35 @@ private T GetService<T>(OutputFormatterWriteContext context)
 
         private string GetResponseBody(object responseObject, IJsonApiContext jsonApiContext, ILogger logger)
         {
+            if (responseObject == null)
+                return GetNullDataResponse();
+
             if (responseObject.GetType() == typeof(Error) || jsonApiContext.RequestEntity == null)
+                return GetErrorJson(responseObject, logger);
+            
+            return JsonApiSerializer.Serialize(responseObject, jsonApiContext);
+        }
+
+        private string GetNullDataResponse()
+        {
+            return JsonConvert.SerializeObject(new Document
             {
-                if (responseObject.GetType() == typeof(Error))
-                {
-                    var errors = new ErrorCollection();
-                    errors.Add((Error)responseObject);
-                    return errors.GetJson();
-                }
-                else
-                {
-                    logger?.LogInformation("Response was not a JSONAPI entity. Serializing as plain JSON.");
-                    return JsonConvert.SerializeObject(responseObject);
-                }
+                Data = null
+            });
+        }
+
+        private string GetErrorJson(object responseObject, ILogger logger)
+        {
+            if (responseObject.GetType() == typeof(Error))
+            {
+                var errors = new ErrorCollection();
+                errors.Add((Error)responseObject);
+                return errors.GetJson();
             }
             else
             {
-                return JsonApiSerializer.Serialize(responseObject, jsonApiContext);
+                logger?.LogInformation("Response was not a JSONAPI entity. Serializing as plain JSON.");
+                return JsonConvert.SerializeObject(responseObject);
             }
         }
     }

src/JsonApiDotNetCore/Internal/ContextGraph.cs

@@ -33,7 +33,7 @@ public object GetRelationship<TParent>(TParent entity, string relationshipName)
                 .FirstOrDefault(p => p.Name.ToLower() == relationshipName.ToLower());
 
             if(navigationProperty == null)
-                return null;
+                throw new JsonApiException("400", $"{parentEntityType} does not contain a relationship named {relationshipName}");
 
             return navigationProperty.GetValue(entity);
         }

src/JsonApiDotNetCore/Models/DocumentBase.cs

@@ -4,9 +4,22 @@
 namespace JsonApiDotNetCore.Models
 {
     public class DocumentBase
-    {        
+    {
         [JsonProperty("included")]
         public List<DocumentData> Included { get; set; }
+
+        [JsonProperty("meta")]
         public Dictionary<string, object> Meta { get; set; }
+
+        // http://www.newtonsoft.com/json/help/html/ConditionalProperties.htm
+        public bool ShouldSerializeIncluded()
+        {
+            return (Included != null);
+        }
+
+        public bool ShouldSerializeMeta()
+        {
+            return (Meta != null);
+        }
     }
 }

src/JsonApiDotNetCore/Serialization/JsonApiDeSerializer.cs

@@ -41,16 +41,16 @@ private static object DataToObject(DocumentData data, IJsonApiContext context)
 
             var contextEntity = context.ContextGraph.GetContextEntity(entityTypeName);
             context.RequestEntity = contextEntity;
-            
+
             var entity = Activator.CreateInstance(contextEntity.EntityType);
-            
+
             entity = _setEntityAttributes(entity, contextEntity, data.Attributes);
             entity = _setRelationships(entity, contextEntity, data.Relationships);
 
             var identifiableEntity = (IIdentifiable)entity;
 
-            if(data.Id != null)
-                identifiableEntity.Id = Convert.ChangeType(data.Id, identifiableEntity.Id.GetType());
+            if (data.Id != null)
+                identifiableEntity.Id = ChangeType(data.Id, identifiableEntity.Id.GetType());
 
             return identifiableEntity;
         }
@@ -70,7 +70,7 @@ private static object _setEntityAttributes(
                 object newValue;
                 if (attributeValues.TryGetValue(attr.PublicAttributeName.Dasherize(), out newValue))
                 {
-                    var convertedValue = Convert.ChangeType(newValue, entityProperty.PropertyType);
+                    var convertedValue = ChangeType(newValue, entityProperty.PropertyType);
                     entityProperty.SetValue(entity, convertedValue);
                 }
             }
@@ -92,22 +92,37 @@ private static object _setRelationships(
 
                 if (entityProperty == null)
                     throw new JsonApiException("400", $"{contextEntity.EntityType.Name} does not contain an relationsip named {attr.RelationshipName}");
-                
+
                 var relationshipName = attr.RelationshipName.Dasherize();
                 RelationshipData relationshipData;
                 if (relationships.TryGetValue(relationshipName, out relationshipData))
                 {
                     var data = (Dictionary<string, string>)relationshipData.ExposedData;
-                    
-                    if(data == null) continue;
-                    
+
+                    if (data == null) continue;
+
                     var newValue = data["id"];
-                    var convertedValue = Convert.ChangeType(newValue, entityProperty.PropertyType);
+                    var convertedValue = ChangeType(newValue, entityProperty.PropertyType);
                     entityProperty.SetValue(entity, convertedValue);
                 }
             }
 
             return entity;
         }
+
+        private static object ChangeType(object value, Type conversion)
+        {
+            var t = conversion;
+
+            if (t.GetTypeInfo().IsGenericType && t.GetGenericTypeDefinition().Equals(typeof(Nullable<>)))
+            {
+                if (value == null)
+                    return null;
+
+                t = Nullable.GetUnderlyingType(t);
+            }
+
+            return Convert.ChangeType(value, t);
+        }
     }
 }

src/JsonApiDotNetCoreExample/Models/TodoItem.cs

@@ -13,7 +13,7 @@ public class TodoItem : Identifiable<int>
         [Attr("ordinal")]
         public long Ordinal { get; set; }
 
-        public int OwnerId { get; set; }
+        public int? OwnerId { get; set; }
         public virtual Person Owner { get; set; }
     }
 }