Avoid logging model errors for invalid fields in value validation

Author: youssefm

src/System.Web.Http/Validation/DefaultBodyModelValidator.cs

@@ -173,6 +173,13 @@ private bool ShallowValidate(ModelMetadata metadata, ValidationContext validatio
                         {
                             key = keyBuilder.AppendTo(key);
                         }
+
+                        // Avoid adding model errors if the model state already contains model errors for that key
+                        // We can't perform this check earlier because we compute the key string only when we detect an error
+                        if (!validationContext.ModelState.IsValidField(key))
+                        {
+                            return false;
+                        }
                     }
                     validationContext.ModelState.AddModelError(key, error.Message);
                     isValid = false;

test/System.Web.Http.Test/Validation/DefaultBodyModelValidatorTest.cs

@@ -143,6 +143,25 @@ public void MultipleValidationErrorsOnSameMemberReported()
             ModelState streetState = actionContext.ModelState["Street"];
             Assert.Equal(2, streetState.Errors.Count);
         }
+
+        [Fact]
+        public void ValidationErrorsNotAddedOnInvalidFields()
+        {
+            // Arrange
+            ModelMetadataProvider metadataProvider = new DataAnnotationsModelMetadataProvider();
+            HttpActionContext actionContext = ContextUtil.CreateActionContext();
+            object model = new Address() { Street = "Microsoft Way" };
+
+            actionContext.ModelState.AddModelError("Street", "error");
+
+            // Act
+            new DefaultBodyModelValidator().Validate(model, typeof(Address), metadataProvider, actionContext, string.Empty);
+
+            // Assert
+            Assert.Contains("Street", actionContext.ModelState.Keys);
+            ModelState streetState = actionContext.ModelState["Street"];
+            Assert.Equal(1, streetState.Errors.Count);
+        }
     }
 
     public class Person