Skipping pre- and post-object-creation callbacks when the target object is definitely already populated

Author: SteveWilkes

AgileMapper.UnitTests/WhenViewingMappingPlans.cs

@@ -266,6 +266,27 @@ public void ShouldNotRangeCheckNullableToNonNullableValues()
             plan.ShouldNotContain("Value.HasValue");
         }
 
+        [Fact]
+        public void ShouldNotAttemptUnnecessaryObjectCreationCallbacks()
+        {
+            using (var mapper = Mapper.CreateNew())
+            {
+                mapper.WhenMapping
+                    .Over<PublicField<string>>()
+                    .Before
+                    .CreatingInstances
+                    .Call(ctx => Console.WriteLine("Nope!"))
+                    .And
+                    .After
+                    .CreatingInstances
+                    .Call(ctx => Console.WriteLine("No way!"));
+
+                string plan = mapper.GetPlanFor<PublicField<string>>().Over<PublicField<string>>();
+
+                plan.ShouldNotContain("Invoke");
+            }
+        }
+
         [Fact]
         public void ShouldShowEnumMismatches()
         {

AgileMapper/Api/Configuration/IPreInstanceCreationCallbackSpecifier.cs

@@ -9,27 +9,40 @@
     /// </summary>
     /// <typeparam name="TSource">The source type to which the configuration should apply.</typeparam>
     /// <typeparam name="TTarget">The target type to which the configuration should apply.</typeparam>
-    public interface IPreInstanceCreationCallbackSpecifier<out TSource, out TTarget>
+    public interface IPreInstanceCreationCallbackSpecifier<TSource, TTarget>
     {
-        /// <summary>
-        /// Configure a callback to call in the configured conditions. The callback is passed a context 
-        /// object containing the current mapping's source and target objects.
-        /// </summary>
+        /// <summary>
+        /// Configure a callback to call in the configured conditions. The callback is passed a context 
+        /// object containing the current mapping's source and target objects.
+        /// </summary>
         /// <param name="callback">The callback to call.</param>
-        void Call(Action<IMappingData<TSource, TTarget>> callback);
+        /// <returns>
+        /// A MappingConfigContinuation to enable further configuration of mappings from and to the source and 
+        /// target type being configured.
+        /// </returns>
+        /// <returns></returns>
+        MappingConfigContinuation<TSource, TTarget> Call(Action<IMappingData<TSource, TTarget>> callback);
 
-        /// <summary>
-        /// Configure a callback to call in the configured conditions. The callback is passed the current 
-        /// mapping's source and target objects.
-        /// </summary>
+        /// <summary>
+        /// Configure a callback to call in the configured conditions. The callback is passed the current 
+        /// mapping's source and target objects.
+        /// </summary>
         /// <param name="callback">The callback to call.</param>
-        void Call(Action<TSource, TTarget> callback);
+        /// <returns>
+        /// A MappingConfigContinuation to enable further configuration of mappings from and to the source and 
+        /// target type being configured.
+        /// </returns>
+        MappingConfigContinuation<TSource, TTarget> Call(Action<TSource, TTarget> callback);
 
-        /// <summary>
-        /// Configure a callback to call in the configured conditions. The callback is passed the current 
-        /// mapping's source and target objects and the current enumerable index, if applicable.
-        /// </summary>
+        /// <summary>
+        /// Configure a callback to call in the configured conditions. The callback is passed the current 
+        /// mapping's source and target objects and the current enumerable index, if applicable.
+        /// </summary>
         /// <param name="callback">The callback to call.</param>
-        void Call(Action<TSource, TTarget, int?> callback);
+        /// <returns>
+        /// A MappingConfigContinuation to enable further configuration of mappings from and to the source and 
+        /// target type being configured.
+        /// </returns>
+        MappingConfigContinuation<TSource, TTarget> Call(Action<TSource, TTarget, int?> callback);
     }
 }

AgileMapper/Api/Configuration/InstanceCreationCallbackSpecifier.cs

@@ -45,17 +45,23 @@ private InstanceCreationCallbackSpecifier<TSource, TTarget, TObject> SetConditio
             return this;
         }
 
-        void IPreInstanceCreationCallbackSpecifier<TSource, TTarget>.Call(
+        MappingConfigContinuation<TSource, TTarget> IPreInstanceCreationCallbackSpecifier<TSource, TTarget>.Call(
             Action<IMappingData<TSource, TTarget>> callback)
-            => CreateCallbackFactory(callback);
+        {
+            return CreateCallbackFactory(callback);
+        }
 
-        void IPreInstanceCreationCallbackSpecifier<TSource, TTarget>.Call(
+        MappingConfigContinuation<TSource, TTarget> IPreInstanceCreationCallbackSpecifier<TSource, TTarget>.Call(
             Action<TSource, TTarget> callback)
-            => CreateCallbackFactory(callback);
+        {
+            return CreateCallbackFactory(callback);
+        }
 
-        void IPreInstanceCreationCallbackSpecifier<TSource, TTarget>.Call(
+        MappingConfigContinuation<TSource, TTarget> IPreInstanceCreationCallbackSpecifier<TSource, TTarget>.Call(
             Action<TSource, TTarget, int?> callback)
-            => CreateCallbackFactory(callback);
+        {
+            return CreateCallbackFactory(callback);
+        }
 
         #endregion
 

AgileMapper/ObjectPopulation/ComplexTypes/PopulationExpressionFactoryBase.cs

@@ -14,8 +14,9 @@ internal abstract class PopulationExpressionFactoryBase
         public IEnumerable<Expression> GetPopulation(IObjectMappingData mappingData)
         {
             var mapperData = mappingData.MapperData;
-            var preCreationCallback = GetCreationCallbackOrNull(Before, mapperData);
-            var postCreationCallback = GetCreationCallbackOrNull(After, mapperData);
+
+            GetCreationCallbacks(mapperData, out var preCreationCallback, out var postCreationCallback);
+
             var populationsAndCallbacks = GetPopulationsAndCallbacks(mappingData).ToList();
 
             yield return preCreationCallback;
@@ -39,6 +40,21 @@ public IEnumerable<Expression> GetPopulation(IObjectMappingData mappingData)
             mappingData.MapperKey.AddSourceMemberTypeTesterIfRequired(mappingData);
         }
 
+        private static void GetCreationCallbacks(
+            IMemberMapperData mapperData,
+            out Expression preCreationCallback,
+            out Expression postCreationCallback)
+        {
+            if (mapperData.TargetIsDefinitelyPopulated())
+            {
+                preCreationCallback = postCreationCallback = null;
+                return;
+            }
+
+            preCreationCallback = GetCreationCallbackOrNull(Before, mapperData);
+            postCreationCallback = GetCreationCallbackOrNull(After, mapperData);
+        }
+
         private static Expression GetCreationCallbackOrNull(CallbackPosition callbackPosition, IMemberMapperData mapperData)
             => mapperData.MapperContext.UserConfigurations.GetCreationCallbackOrNull(callbackPosition, mapperData);