Introduced [MapToParent] functionality to TopicMappingService

The `[MapToParent]` capability was originally introduced as part of the `ReverseTopicMappingService`, to allow complex binding models to be mapped back to a single `Topic` entity. There's no reason the opposite shouldn't also be supported—nor is it all that difficult to add this feature. This commit introduces the initial versionof this.

Author: JeremyCaney

OnTopic.Tests/TestDoubles/FakeViewModelLookupService.cs

@@ -43,6 +43,7 @@ public FakeViewModelLookupService() : base(null, typeof(object)) {
       Add(typeof(FlattenChildrenTopicViewModel));
       Add(typeof(InheritedPropertyTopicViewModel));
       Add(typeof(KeyOnlyTopicViewModel));
+      Add(typeof(MapToParentTopicViewModel));
       Add(typeof(MethodBasedViewModel));
       Add(typeof(MinimumLengthPropertyTopicViewModel));
       Add(typeof(NestedTopicViewModel));

OnTopic.Tests/TopicMappingServiceTest.cs

@@ -397,6 +397,32 @@ public async Task Map_Children_ReturnsMappedModel() {
       ));
     }
 
+    /*==========================================================================================================================
+    | TEST: MAP: MAP TO PARENT: RETURNS MAPPED MODEL
+    \-------------------------------------------------------------------------------------------------------------------------*/
+    /// <summary>
+    ///   Establishes a <see cref="TopicMappingService"/> and tests whether the resulting object's nested complex objects are
+    ///   property mapped with attribute values from the parent, based on their <see cref="MapToParentAttribute"/>
+    ///   configuration.
+    /// </summary>
+    [TestMethod]
+    public async Task Map_MapToParent_ReturnsMappedModel() {
+
+      var topic                 = TopicFactory.Create("Test", "FlattenChildren");
+
+      topic.Attributes.SetValue("PrimaryKey", "Primary Key");
+      topic.Attributes.SetValue("AlternateKey", "Alternate Key");
+      topic.Attributes.SetValue("AncillaryKey", "Ancillary Key");
+      topic.Attributes.SetValue("AliasedKey", "Aliased Key");
+
+      var target = await _mappingService.MapAsync<MapToParentTopicViewModel>(topic).ConfigureAwait(false);
+
+      Assert.AreEqual<string>("Test", target.Primary.Key);
+      Assert.AreEqual<string>("Aliased Key", target.Alternate.Key);
+      Assert.AreEqual<string>("Ancillary Key", target.Ancillary.Key);
+
+    }
+
     /*==========================================================================================================================
     | TEST: MAP: TOPIC REFERENCES: RETURNS MAPPED MODEL
     \-------------------------------------------------------------------------------------------------------------------------*/

OnTopic.Tests/ViewModels/MapToParentTopicViewModel.cs

@@ -0,0 +1,31 @@
+/*==============================================================================================================================
+| Author        Ignia, LLC
+| Client        Ignia, LLC
+| Project       Topics Library
+\=============================================================================================================================*/
+using OnTopic.Mapping.Annotations;
+
+namespace OnTopic.Tests.ViewModels {
+
+  /*============================================================================================================================
+  | VIEW MODEL: MAP TO PARENT
+  \---------------------------------------------------------------------------------------------------------------------------*/
+  /// <summary>
+  ///   Provides a strongly-typed data transfer object for testing views with the <see cref="MapToParentAttribute"/>.
+  /// </summary>
+  /// <remarks>
+  ///   This is a sample class intended for test purposes only; it is not designed for use in a production environment.
+  /// </remarks>
+  public class MapToParentTopicViewModel {
+
+    [MapToParent(AttributePrefix = "")]
+    public KeyOnlyTopicViewModel? Primary { get; set; } = new KeyOnlyTopicViewModel();
+
+    [MapToParent(AttributePrefix = "Aliased")]
+    public KeyOnlyTopicViewModel? Alternate { get; set; } = new KeyOnlyTopicViewModel();
+
+    [MapToParent]
+    public KeyOnlyTopicViewModel? Ancillary { get; set; } = new KeyOnlyTopicViewModel();
+
+  } //Class
+} //Namespace

OnTopic/Mapping/README.md

@@ -103,10 +103,10 @@ To support the mapping, a variety of `Attribute` classes are provided for decora
 - **`[Relationship(key, type)]`**: For a collection, optionally specifies the name of the key to look for, instead of the property name, and the relationship type, in case the key name is ambiguous.
 - **`[Follow(relationships)]`**: Instructs the code to populate the specified relationships on any view models within a collection.
 - **`[Flatten]`**: Includes all descendants for every item in the collection. If the collection enforces uniqueness, duplicates will be removed.
+- **`[MapToParent]`**: Allows the attributes of a topic to be applied to a child complex object, optionally including a prefix.
 
 ### `ReverseTopicMappingService`
 - **`[DisableMapping]`**: Prevents the `ReverseTopicMappingService` from attempting to map the property back to the target `Topic`.
-- **`[MapToParent]`**: Allows the `ReverseTopicMappingService` to map a complex property type back to a `Topic`.
 
 ### Example
 The following is an example of a data transfer object that implements the above attributes:

OnTopic/Mapping/TopicMappingService.cs

@@ -85,8 +85,14 @@ public TopicMappingService(ITopicRepository topicRepository, ITypeLookupService
     /// <param name="topic">The <see cref="Topic"/> entity to derive the data from.</param>
     /// <param name="relationships">Determines what relationships the mapping should follow, if any.</param>
     /// <param name="cache">A cache to keep track of already-mapped object instances.</param>
+    /// <param name="attributePrefix">The prefix to apply to the attributes.</param>
     /// <returns>An instance of the dynamically determined View Model with properties appropriately mapped.</returns>
-    private async Task<object?> MapAsync(Topic? topic, Relationships relationships, ConcurrentDictionary<int, object> cache) {
+    private async Task<object?> MapAsync(
+      Topic?                    topic,
+      Relationships             relationships,
+      ConcurrentDictionary<int, object> cache,
+      string?                   attributePrefix                 = null
+    ) {
 
       /*------------------------------------------------------------------------------------------------------------------------
       | Validate input
@@ -119,7 +125,7 @@ public TopicMappingService(ITopicRepository topicRepository, ITypeLookupService
       /*------------------------------------------------------------------------------------------------------------------------
       | Provide mapping
       \-----------------------------------------------------------------------------------------------------------------------*/
-      return await MapAsync(topic, target, relationships, cache).ConfigureAwait(false);
+      return await MapAsync(topic, target, relationships, cache, attributePrefix).ConfigureAwait(false);
 
     }
 
@@ -150,6 +156,7 @@ public TopicMappingService(ITopicRepository topicRepository, ITypeLookupService
     /// <param name="target">The target object to map the data to.</param>
     /// <param name="relationships">Determines what relationships the mapping should follow, if any.</param>
     /// <param name="cache">A cache to keep track of already-mapped object instances.</param>
+    /// <param name="attributePrefix">The prefix to apply to the attributes.</param>
     /// <remarks>
     ///   This internal version passes a private cache of mapped objects from this run. This helps prevent problems with
     ///   recursion in case <see cref="Topic"/> is referred to multiple times (e.g., a <c>Children</c> collection with
@@ -162,7 +169,8 @@ private async Task<object> MapAsync(
       Topic? topic,
       object target,
       Relationships relationships,
-      ConcurrentDictionary<int, object> cache
+      ConcurrentDictionary<int, object> cache,
+      string?                   attributePrefix                 = null
     ) {
 
       /*------------------------------------------------------------------------------------------------------------------------
@@ -194,7 +202,7 @@ ConcurrentDictionary<int, object> cache
       \-----------------------------------------------------------------------------------------------------------------------*/
       var taskQueue = new List<Task>();
       foreach (var property in _typeCache.GetMembers<PropertyInfo>(target.GetType())) {
-        taskQueue.Add(SetPropertyAsync(topic, target, relationships, property, cache));
+        taskQueue.Add(SetPropertyAsync(topic, target, relationships, property, cache, attributePrefix));
       }
       await Task.WhenAll(taskQueue.ToArray()).ConfigureAwait(false);
 
@@ -217,12 +225,14 @@ ConcurrentDictionary<int, object> cache
     /// <param name="relationships">Determines what relationships the mapping should follow, if any.</param>
     /// <param name="property">Information related to the current property.</param>
     /// <param name="cache">A cache to keep track of already-mapped object instances.</param>
+    /// <param name="attributePrefix">The prefix to apply to the attributes.</param>
     protected async Task SetPropertyAsync(
       Topic source,
       object target,
       Relationships relationships,
       PropertyInfo property,
-      ConcurrentDictionary<int, object> cache
+      ConcurrentDictionary<int, object> cache,
+      string?                   attributePrefix                 = null
     ) {
 
       /*------------------------------------------------------------------------------------------------------------------------
@@ -237,7 +247,7 @@ ConcurrentDictionary<int, object> cache
       /*------------------------------------------------------------------------------------------------------------------------
       | Establish per-property variables
       \-----------------------------------------------------------------------------------------------------------------------*/
-      var configuration         = new PropertyConfiguration(property);
+      var configuration         = new PropertyConfiguration(property, attributePrefix);
       var topicReferenceId      = source.Attributes.GetInteger($"{configuration.AttributeKey}Id", 0);
 
       if (topicReferenceId == 0 && configuration.AttributeKey.EndsWith("Id", StringComparison.InvariantCultureIgnoreCase)) {
@@ -274,6 +284,15 @@ ConcurrentDictionary<int, object> cache
           await SetTopicReferenceAsync(topicReference, target, configuration, cache).ConfigureAwait(false);
         }
       }
+      else if (configuration.MapToParent) {
+        await MapAsync(
+          source,
+          property.GetValue(target),
+          relationships,
+          cache,
+          configuration.AttributePrefix
+        ).ConfigureAwait(false);
+      }
 
       /*------------------------------------------------------------------------------------------------------------------------
       | Validate fields