Metadata: Disallow backing field on indexer property

- Don't discover backing field for indexer property by convention - Throw if trying to set a backing field for indexer property Resolves #19448
dotnet · Jan 1, 2020 · a8072e9 · a8072e9
1 parent ddf496f
commit a8072e9
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Showing 5 changed files with 54 additions and 1 deletion.
diff --git a/src/EFCore/Metadata/Conventions/BackingFieldConvention.cs b/src/EFCore/Metadata/Conventions/BackingFieldConvention.cs
@@ -84,7 +84,8 @@ public virtual void ProcessNavigationAdded(
         private FieldInfo GetFieldToSet(IConventionPropertyBase propertyBase)
         {
             if (propertyBase == null
-                || !ConfigurationSource.Convention.Overrides(propertyBase.GetFieldInfoConfigurationSource()))
+                || !ConfigurationSource.Convention.Overrides(propertyBase.GetFieldInfoConfigurationSource())
+                || propertyBase.IsIndexerProperty())
             {
                 return null;
             }

diff --git a/src/EFCore/Metadata/Internal/PropertyBase.cs b/src/EFCore/Metadata/Internal/PropertyBase.cs
@@ -151,6 +151,13 @@ public virtual void SetField([CanBeNull] FieldInfo fieldInfo, ConfigurationSourc
             if (fieldInfo != null)
             {
                 IsCompatible(fieldInfo, ClrType, DeclaringType.ClrType, Name, shouldThrow: true);
+
+                if (PropertyInfo != null
+                    && PropertyInfo.IsIndexerProperty())
+                {
+                    throw new InvalidOperationException(
+                        CoreStrings.BackingFieldOnIndexer(fieldInfo.GetSimpleMemberName(), DeclaringType.DisplayName(), Name));
+                }
             }
 
             if (PropertyInfo == null

diff --git a/src/EFCore/Properties/CoreStrings.Designer.cs b/src/EFCore/Properties/CoreStrings.Designer.cs
diff --git a/src/EFCore/Properties/CoreStrings.resx b/src/EFCore/Properties/CoreStrings.resx
@@ -1248,4 +1248,7 @@
   <data name="NonIndexerEntityType" xml:space="preserve">
     <value>Cannot add property '{property}' on entity type '{entity}' since there is no indexer on '{entity}' taking a single argument of type '{type}'.</value>
   </data>
+  <data name="BackingFieldOnIndexer" xml:space="preserve">
+    <value>Cannot set backing field '{field}' for the indexer property '{entityType}.{property}'. Indexer properties are not allowed to use a backing field.</value>
+  </data>
 </root>
diff --git a/test/EFCore.Tests/Metadata/Conventions/BackingFieldConventionTest.cs b/test/EFCore.Tests/Metadata/Conventions/BackingFieldConventionTest.cs
@@ -241,6 +241,29 @@ public void FieldInfo_set_by_annotation_is_used()
             Assert.Equal("m_onTheRun", property.GetFieldName());
         }
 
+        [ConditionalFact]
+        public void Backing_field_is_not_discovered_for_indexer_property()
+        {
+            var entityType = CreateModel().AddEntityType(typeof(IndexedClass));
+            var property = entityType.AddIndexedProperty("Nation", typeof(string));
+
+            RunConvention(property);
+            Validate(property);
+
+            Assert.Null(property.GetFieldName());
+        }
+
+        [ConditionalFact]
+        public void Setting_field_on_indexer_property_throws()
+        {
+            var entityType = CreateModel().AddEntityType(typeof(IndexedClass));
+            var property = entityType.AddIndexedProperty("Nation", typeof(string));
+
+            Assert.Equal(
+                CoreStrings.BackingFieldOnIndexer("nation", entityType.DisplayName(), "Nation"),
+                Assert.Throws<InvalidOperationException>(() => property.SetField("nation")).Message);
+        }
+
         private void RunConvention(IMutableProperty property)
             => new BackingFieldConvention(CreateDependencies())
                 .ProcessPropertyAdded(
@@ -459,6 +482,17 @@ public object OnTheRun
             }
         }
 
+        private class IndexedClass
+        {
+            private string nation;
+            private string _nation;
+            private string _Nation;
+            private string m_nation;
+            private string m_Nation;
+
+            public object this[string name] => null;
+        }
+
 #pragma warning disable RCS1222 // Merge preprocessor directives.
 #pragma warning restore 649, 169
 #pragma warning restore IDE0027 // Use expression body for accessors