Added tests for serialization callbacks

Author: Bart Koelman

src/JsonApiDotNetCore/Serialization/FieldsToSerialize.cs

@@ -19,6 +19,9 @@ public class FieldsToSerialize : IFieldsToSerialize
         private readonly IJsonApiRequest _request;
         private readonly SparseFieldSetCache _sparseFieldSetCache;
 
+        /// <inheritdoc />
+        public bool ShouldSerialize => _request.Kind != EndpointKind.Relationship;
+
         public FieldsToSerialize(IResourceContextProvider resourceContextProvider, IEnumerable<IQueryConstraintProvider> constraintProviders,
             IResourceDefinitionAccessor resourceDefinitionAccessor, IJsonApiRequest request)
         {
@@ -35,7 +38,7 @@ public IReadOnlyCollection<AttrAttribute> GetAttributes(Type resourceType)
         {
             ArgumentGuard.NotNull(resourceType, nameof(resourceType));
 
-            if (_request.Kind == EndpointKind.Relationship)
+            if (!ShouldSerialize)
             {
                 return Array.Empty<AttrAttribute>();
             }
@@ -56,7 +59,7 @@ public IReadOnlyCollection<RelationshipAttribute> GetRelationships(Type resource
         {
             ArgumentGuard.NotNull(resourceType, nameof(resourceType));
 
-            if (_request.Kind == EndpointKind.Relationship)
+            if (!ShouldSerialize)
             {
                 return Array.Empty<RelationshipAttribute>();
             }

src/JsonApiDotNetCore/Serialization/IFieldsToSerialize.cs

@@ -10,6 +10,11 @@ namespace JsonApiDotNetCore.Serialization
     /// </summary>
     public interface IFieldsToSerialize
     {
+        /// <summary>
+        /// Indicates whether attributes and relationships should be serialized, based on the current endpoint.
+        /// </summary>
+        bool ShouldSerialize { get; }
+
         /// <summary>
         /// Gets the collection of attributes that are to be serialized for resources of type <paramref name="resourceType" />.
         /// </summary>

src/JsonApiDotNetCore/Serialization/RequestDeserializer.cs

@@ -64,7 +64,7 @@ public object Deserialize(string body)
 
             object instance = DeserializeBody(body);
 
-            if (instance is IIdentifiable resource)
+            if (instance is IIdentifiable resource && _request.Kind != EndpointKind.Relationship)
             {
                 _resourceDefinitionAccessor.OnDeserialize(resource);
             }

src/JsonApiDotNetCore/Serialization/ResponseSerializer.cs

@@ -96,7 +96,7 @@ private string SerializeErrorDocument(ErrorDocument errorDocument)
         /// </remarks>
         internal string SerializeSingle(IIdentifiable resource)
         {
-            if (resource != null)
+            if (resource != null && _fieldsToSerialize.ShouldSerialize)
             {
                 _resourceDefinitionAccessor.OnSerialize(resource);
             }
@@ -128,9 +128,12 @@ internal string SerializeSingle(IIdentifiable resource)
         /// </remarks>
         internal string SerializeMany(IReadOnlyCollection<IIdentifiable> resources)
         {
-            foreach (IIdentifiable resource in resources)
+            if (_fieldsToSerialize.ShouldSerialize)
             {
-                _resourceDefinitionAccessor.OnSerialize(resource);
+                foreach (IIdentifiable resource in resources)
+                {
+                    _resourceDefinitionAccessor.OnSerialize(resource);
+                }
             }
 
             IReadOnlyCollection<AttrAttribute> attributes = _fieldsToSerialize.GetAttributes(_primaryResourceType);

test/JsonApiDotNetCoreExampleTests/IntegrationTests/AtomicOperations/ResourceDefinitions/Serialization/AtomicSerializationHitCounter.cs

@@ -0,0 +1,24 @@
+namespace JsonApiDotNetCoreExampleTests.IntegrationTests.AtomicOperations.ResourceDefinitions.Serialization
+{
+    public sealed class AtomicSerializationHitCounter
+    {
+        internal int DeserializeCount { get; private set; }
+        internal int SerializeCount { get; private set; }
+
+        internal void Reset()
+        {
+            DeserializeCount = 0;
+            SerializeCount = 0;
+        }
+
+        internal void IncrementDeserializeCount()
+        {
+            DeserializeCount++;
+        }
+
+        internal void IncrementSerializeCount()
+        {
+            SerializeCount++;
+        }
+    }
+}