chore: rename affected resource helpers, add comments

Author: maurei

src/JsonApiDotNetCore/Hooks/Execution/AffectedResourceDiff.cs

@@ -17,10 +17,10 @@ namespace JsonApiDotNetCore.Hooks
     public interface IAffectedResourcesDiff<TEntity> :  IAffectedResources<TEntity> where TEntity : class, IIdentifiable
     {
         HashSet<TEntity> DatabaseValues { get; }
-        IEnumerable<ResourceDiffPair<TEntity>> GetDiff();
+        IEnumerable<ResourceDiffPair<TEntity>> GetDiffs();
     }
 
-    public  class ResourceDiff<TEntity> : AffectedResources<TEntity>, IAffectedResourcesDiff<TEntity> where TEntity : class, IIdentifiable
+    public  class AffectedResourceDiff<TEntity> : AffectedResources<TEntity>, IAffectedResourcesDiff<TEntity> where TEntity : class, IIdentifiable
     {
 
         private readonly HashSet<TEntity> _databaseValues;
@@ -31,20 +31,22 @@ public  class ResourceDiff<TEntity> : AffectedResources<TEntity>, IAffectedResou
         /// </summary>
         public HashSet<TEntity> DatabaseValues { get => _databaseValues ?? ThrowNoDbValuesError(); }
 
-        public ResourceDiff(IEnumerable requestEntities,
+        public AffectedResourceDiff(IEnumerable requestEntities,
                           IEnumerable databaseEntities,
                           Dictionary<RelationshipAttribute, IEnumerable> relationships) : base(requestEntities, relationships)
         {
             _databaseValues = (HashSet<TEntity>)databaseEntities;
             _databaseValuesLoaded |= _databaseValues != null;
         }
 
-        public IEnumerable<ResourceDiffPair<TEntity>> GetDiff()
+        public IEnumerable<ResourceDiffPair<TEntity>> GetDiffs()
         {
+            if (!_databaseValuesLoaded) ThrowNoDbValuesError();
+
             foreach (var entity in Entities)
             {
                 TEntity currentValueInDatabase = null;
-                if (_databaseValuesLoaded) currentValueInDatabase = _databaseValues.Single(e => entity.StringId == e.StringId);
+                currentValueInDatabase = _databaseValues.Single(e => entity.StringId == e.StringId);
                 yield return new ResourceDiffPair<TEntity>(entity, currentValueInDatabase);
             }
         }

src/JsonApiDotNetCore/Hooks/ResourceHookExecutor.cs

@@ -49,7 +49,7 @@ public virtual IEnumerable<TEntity> BeforeUpdate<TEntity>(IEnumerable<TEntity> e
             {
                 var relationships = node.RelationshipsToNextLayer.Select(p => p.Attribute).ToArray();
                 var dbValues = LoadDbValues(typeof(TEntity), (IEnumerable<TEntity>)node.UniqueEntities, ResourceHook.BeforeUpdate, relationships);
-                var diff = new ResourceDiff<TEntity>(node.UniqueEntities, dbValues, node.PrincipalsToNextLayer());
+                var diff = new AffectedResourceDiff<TEntity>(node.UniqueEntities, dbValues, node.PrincipalsToNextLayer());
                 IEnumerable<TEntity> updated = container.BeforeUpdate(diff, pipeline);
                 node.UpdateUnique(updated);
                 node.Reassign(entities);

test/UnitTests/ResourceHooks/ResourceHookExecutor/Update/BeforeUpdate_WithDbValues_Tests.cs

@@ -210,7 +210,7 @@ public void BeforeUpdate_NoImplicit_Without_Child_Hook_Implemented()
 
         private bool TodoCheck(IAffectedResourcesDiff<TodoItem> diff, string checksum)
         {
-            var diffPair = diff.GetDiff().Single();
+            var diffPair = diff.GetDiffs().Single();
             var dbCheck = diffPair.DatabaseValue.Description == checksum;
             var reqCheck = diffPair.Entity.Description == null;
             return (dbCheck && reqCheck);

test/UnitTests/ResourceHooks/ResourceHooksTestsSetup.cs

@@ -262,7 +262,7 @@ void MockHooks<TModel>(Mock<IResourceHookContainer<TModel>> resourceDefinition)
             .Verifiable();
             resourceDefinition
             .Setup(rd => rd.BeforeUpdate(It.IsAny<IAffectedResourcesDiff<TModel>>(), It.IsAny<ResourcePipeline>()))
-            .Returns<ResourceDiff<TModel>, ResourcePipeline>((entityDiff, context) => entityDiff.Entities)
+            .Returns<AffectedResourceDiff<TModel>, ResourcePipeline>((entityDiff, context) => entityDiff.Entities)
             .Verifiable();
             resourceDefinition
             .Setup(rd => rd.BeforeDelete(It.IsAny<IAffectedResources<TModel>>(), It.IsAny<ResourcePipeline>()))