From 1e094dcfcabf81d9f668cbc6666945618b1e9023 Mon Sep 17 00:00:00 2001
From: Sylvain Prieur <sylvain.prieur@microsoft.com>
Date: Fri, 1 Nov 2019 13:40:17 -0700
Subject: [PATCH] Fixes for Csdl.GetNamespaceAlias extension method. (#1586)

* Fixes for Csdl.GetNamespaceAlias extension method.

- GetNamespace's documentation advertises returning null if the namespace doesn't have an alias.
However, it throws KeyNotFoundException instead, as it's calling VersioningDictionary.Get.
- GetNamespace crashes with NullReferenceException if the CSDL doesn't define any namespace alias.
A null check for GetAnnotationValue's return value is missing.

* Adjusted for older .NET versions.

* Unit tests

* Positive test case for GetNamespaceAlias
---
 .../Csdl/SerializationExtensionMethods.cs     |  9 ++++++++-
 .../ExtensionMethods/ExtensionMethodTests.cs  | 20 +++++++++++++++++++
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/src/Microsoft.OData.Edm/Csdl/SerializationExtensionMethods.cs b/src/Microsoft.OData.Edm/Csdl/SerializationExtensionMethods.cs
index 0c5ba2c453..ab7411361a 100644
--- a/src/Microsoft.OData.Edm/Csdl/SerializationExtensionMethods.cs
+++ b/src/Microsoft.OData.Edm/Csdl/SerializationExtensionMethods.cs
@@ -270,8 +270,15 @@ public static void SetNamespaceAlias(this IEdmModel model, string namespaceName,
         /// <returns>The alias of the given namespace, or null if one does not exist.</returns>
         public static string GetNamespaceAlias(this IEdmModel model, string namespaceName)
         {
+            EdmUtil.CheckArgumentNull(model, "model");
             VersioningDictionary<string, string> mappings = model.GetAnnotationValue<VersioningDictionary<string, string>>(model, EdmConstants.InternalUri, CsdlConstants.NamespaceAliasAnnotation);
-            return mappings.Get(namespaceName);
+            string namespaceAlias;
+            if (mappings != null && mappings.TryGetValue(namespaceName, out namespaceAlias))
+            {
+                return namespaceAlias;
+            }
+
+            return null;
         }
 
         // This internal method exists so we can get a consistent view of the mappings through the entire serialization process.
diff --git a/test/FunctionalTests/Microsoft.OData.Edm.Tests/ExtensionMethods/ExtensionMethodTests.cs b/test/FunctionalTests/Microsoft.OData.Edm.Tests/ExtensionMethods/ExtensionMethodTests.cs
index 2d2cd602fc..dd32c6c742 100644
--- a/test/FunctionalTests/Microsoft.OData.Edm.Tests/ExtensionMethods/ExtensionMethodTests.cs
+++ b/test/FunctionalTests/Microsoft.OData.Edm.Tests/ExtensionMethods/ExtensionMethodTests.cs
@@ -937,6 +937,26 @@ public void FindTypeForUndefinedTypeDoesnotGetIntoInfiniteSearchLoop()
             Assert.Null(unknownType);
         }
 
+        [Fact]
+        public void GetNamespaceAliasReturnsNullForNamespaceWithoutAlias()
+        {
+            Assert.Null(TestModel.Instance.Model.GetNamespaceAlias("SomeNamespace.NotIn.Model"));
+        }
+
+        [Fact]
+        public void GetNamespaceAliasReturnsNullForModelsWithoutAliases()
+        {
+            EdmModel model = new EdmModel(false);
+            Assert.Null(model.GetNamespaceAlias("SomeNamespace"));
+        }
+
+        [Fact]
+        public void GetNamespaceAliasForNamespaceWithAlias()
+        {
+            Assert.Equal(TestModel.TestModelAlias, TestModel.Instance.Model.GetNamespaceAlias(TestModel.TestModelNameSpace));
+            Assert.Equal(TestModel.TestModelAlias2, TestModel.Instance.Model.GetNamespaceAlias(TestModel.TestModelNameSpace2));
+        }
+        
         internal class TestModel
         {
             public static TestModel Instance = new TestModel();