Decoupled ParseObject subclassing

Similar to the subclassing architecture used on iOS, this abstracts and cleans up all of the code relating to subclassing that currently resides inside of ParseObject.

Author: richardjrossiii

Parse/Compat/Tuple.cs

@@ -4,7 +4,11 @@
 using System.Text;
 
 namespace System {
-  internal static class Tuple {
+  internal static class Tuple {
+    // This is useful because it allows for type inference, which normally cannot be done with constructors, but can be done for static methods.
+    public static Tuple<T1, T2> Create<T1, T2>(T1 t1, T2 t2) {
+      return new Tuple<T1, T2>(t1, t2);
+    }
   }
 
   internal class Tuple<T1, T2> {

Parse/Compat/Type.cs

@@ -0,0 +1,18 @@
+using System;
+
+namespace System {
+  /// <summary>
+  /// Unity does not have an API for GetTypeInfo(), instead they expose most of the methods
+  /// on System.Reflection.TypeInfo on the type itself. This poses a problem for compatibility
+  /// with the rest of the C# world, as we expect the result of GetTypeInfo() to be an actual TypeInfo,
+  /// as well as be able to be converted back to a type using AsType().
+  ///
+  /// This class simply implements some of the simple missing methods on Type to make it as API-compatible
+  /// as possible to TypeInfo.
+  /// </summary>
+  internal static class TypeExtensions {
+    public static Type AsType(this Type type) {
+      return type;
+    }
+  }
+}

Parse/Internal/Object/Subclassing/IObjectSubclassingController.cs

@@ -0,0 +1,20 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Parse.Internal {
+  internal interface IObjectSubclassingController {
+    String GetClassName(Type type);
+    Type GetType(String className);
+
+    bool IsTypeValid(String className, Type type);
+
+    void RegisterSubclass(Type t);
+    void UnregisterSubclass(Type t);
+
+    ParseObject Instantiate(String className);
+    IDictionary<String, String> GetPropertyMappings(String className);
+  }
+}

Parse/Internal/Object/Subclassing/ObjectSubclassInfo.cs

@@ -0,0 +1,40 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
+using System.Reflection;
+
+#if UNITY
+using TypeInfo = System.Type;
+#endif
+
+namespace Parse.Internal {
+  internal class ObjectSubclassInfo {
+    public ObjectSubclassInfo(Type type, ConstructorInfo constructor) {
+      TypeInfo = type.GetTypeInfo();
+      ClassName = GetClassName(TypeInfo);
+      Constructor = constructor;
+      PropertyMappings = type.GetProperties()
+        .Select(prop => Tuple.Create(prop, prop.GetCustomAttribute<ParseFieldNameAttribute>(true)))
+        .Where(t => t.Item2 != null)
+        .Select(t => Tuple.Create(t.Item1, t.Item2.FieldName))
+        .ToDictionary(t => t.Item1.Name, t => t.Item2);
+    }
+
+    public TypeInfo TypeInfo { get; private set; }
+    public String ClassName { get; private set; }
+    public IDictionary<String, String> PropertyMappings { get; private set; }
+    private ConstructorInfo Constructor { get; set; }
+
+    public ParseObject Instantiate() {
+      return (ParseObject)Constructor.Invoke(null);
+    }
+
+    internal static String GetClassName(TypeInfo type) {
+      var attribute = type.GetCustomAttribute<ParseClassNameAttribute>();
+      return attribute != null ? attribute.ClassName : null;
+    }
+  }
+}

Parse/Internal/Object/Subclassing/ObjectSubclassingController.cs

@@ -0,0 +1,127 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection;
+using System.Threading;
+
+#if UNITY
+using TypeInfo = System.Type;
+#endif
+
+namespace Parse.Internal {
+  internal class ObjectSubclassingController : IObjectSubclassingController {
+    private readonly ReaderWriterLockSlim mutex;
+    private readonly IDictionary<String, ObjectSubclassInfo> registeredSubclasses;
+    private IDictionary<String, Action> registerActions;
+
+    public ObjectSubclassingController(IDictionary<Type, Action> actions) {
+      mutex = new ReaderWriterLockSlim();
+      registeredSubclasses = new Dictionary<String, ObjectSubclassInfo>();
+      registerActions = actions.ToDictionary(p => GetClassName(p.Key), p => p.Value);
+    }
+
+    public String GetClassName(Type type) {
+      return ObjectSubclassInfo.GetClassName(type.GetTypeInfo());
+    }
+
+    public Type GetType(String className) {
+      ObjectSubclassInfo info = null;
+      mutex.EnterReadLock();
+      registeredSubclasses.TryGetValue(className, out info);
+      mutex.ExitReadLock();
+
+      return info != null
+        ? info.TypeInfo.AsType()
+        : null;
+    }
+
+    public bool IsTypeValid(String className, Type type) {
+      ObjectSubclassInfo subclassInfo = null;
+
+      mutex.EnterReadLock();
+      registeredSubclasses.TryGetValue(className, out subclassInfo);
+      mutex.ExitReadLock();
+
+      return subclassInfo == null
+        ? type == typeof(ParseObject)
+        : subclassInfo.TypeInfo == type.GetTypeInfo();
+    }
+
+    public void RegisterSubclass(Type type) {
+      TypeInfo typeInfo = type.GetTypeInfo();
+      if (!typeInfo.IsSubclassOf(typeof(ParseObject))) {
+        throw new ArgumentException("Cannot register a type that is not a subclass of ParseObject");
+      }
+
+      String className = ObjectSubclassInfo.GetClassName(typeInfo);
+
+      try {
+        // Perform this as a single independent transaction, so we can never get into an
+        // intermediate state where we *theoretically* register the wrong class due to a
+        // TOCTTOU bug.
+        mutex.EnterWriteLock();
+
+        ObjectSubclassInfo previousInfo = null;
+        if (registeredSubclasses.TryGetValue(className, out previousInfo)) {
+          if (typeInfo.IsAssignableFrom(previousInfo.TypeInfo)) {
+            // Previous subclass is more specific or equal to the current type, do nothing.
+            return;
+          } else if (previousInfo.TypeInfo.IsAssignableFrom(typeInfo)) {
+            // Previous subclass is parent of new child, fallthrough and actually register
+            // this class.
+            /* Do nothing */
+          } else {
+            throw new ArgumentException(
+              "Tried to register both " + previousInfo.TypeInfo.FullName + " and " + typeInfo.FullName +
+              " as the ParseObject subclass of " + className + ". Cannot determine the right class " +
+              "to use because neither inherits from the other."
+            );
+          }
+        }
+
+        ConstructorInfo constructor = type.FindConstructor();
+        if (constructor == null) {
+          throw new ArgumentException("Cannot register a type that does not implement the default constructor!");
+        }
+
+        registeredSubclasses[className] = new ObjectSubclassInfo(type, constructor);
+      } finally {
+        mutex.ExitWriteLock();
+      }
+
+      Action toPerform = null;
+      if (registerActions.TryGetValue(className, out toPerform)) {
+        toPerform();
+      }
+    }
+
+    public void UnregisterSubclass(Type type) {
+      mutex.EnterWriteLock();
+      registeredSubclasses.Remove(GetClassName(type));
+      mutex.ExitWriteLock();
+    }
+
+    public ParseObject Instantiate(String className) {
+      ObjectSubclassInfo info = null;
+
+      mutex.EnterReadLock();
+      registeredSubclasses.TryGetValue(className, out info);
+      mutex.ExitReadLock();
+
+      return info != null
+        ? info.Instantiate()
+        : new ParseObject(className);
+    }
+
+    public IDictionary<String, String> GetPropertyMappings(String className) {
+      ObjectSubclassInfo info = null;
+      mutex.EnterReadLock();
+      registeredSubclasses.TryGetValue(className, out info);
+      mutex.ExitReadLock();
+
+      return info != null
+        ? info.PropertyMappings
+        : null;
+    }
+  }
+}

Parse/Internal/ParseCorePlugins.cs

@@ -28,7 +28,8 @@ public static ParseCorePlugins Instance {
     private IParseSessionController sessionController;
     private IParseUserController userController;
     private IParsePushController pushController;
-    private IParsePushChannelsController pushChannelsController;
+    private IParsePushChannelsController pushChannelsController;
+    private IObjectSubclassingController subclassingController;
 
     #endregion
 
@@ -242,6 +243,25 @@ internal set {
           currentUserController = value;
         }
       }
+    }
+
+    public IObjectSubclassingController SubclassingController {
+      get {
+        lock (mutex) {
+          subclassingController = subclassingController ?? new ObjectSubclassingController(new Dictionary<Type, Action> {
+            // Do these as explicit closures instead of method references,
+            // as we should still lazy-load the controllers.
+            { typeof(ParseUser), () => CurrentUserController.ClearFromMemory() },
+            { typeof(ParseInstallation), () => CurrentInstallationController.ClearFromMemory() }
+          });
+          return subclassingController;
+        }
+      }
+      internal set {
+        lock (mutex) {
+          subclassingController = value;
+        }
+      }
     }
   }
 }

Parse/Internal/ReflectionHelpers.cs

@@ -50,8 +50,9 @@ internal static bool IsConstructedGenericType(this Type type) {
     internal static IEnumerable<ConstructorInfo> GetConstructors(this Type type) {
 #if UNITY
       return type.GetConstructors();
-#else
-      return type.GetTypeInfo().DeclaredConstructors;
+#else
+      return type.GetTypeInfo().DeclaredConstructors
+        .Where(c => (c.Attributes & MethodAttributes.Static) == 0);
 #endif
     }
 
@@ -78,7 +79,7 @@ from constructor in self.GetConstructors()
         let types = from p in parameters select p.ParameterType
         where types.SequenceEqual(parameterTypes)
         select constructor;
-      return constructors.Single();
+      return constructors.SingleOrDefault();
     }
 
     internal static PropertyInfo GetProperty(this Type type, string name) {

Parse/Parse.Android.csproj

@@ -73,6 +73,9 @@
     <Compile Include="Internal\Object\Controller\ParseObjectController.cs" />
     <Compile Include="Internal\Object\State\IObjectState.cs" />
     <Compile Include="Internal\Object\State\MutableObjectState.cs" />
+    <Compile Include="Internal\Object\Subclassing\IObjectSubclassingController.cs" />
+    <Compile Include="Internal\Object\Subclassing\ObjectSubclassInfo.cs" />
+    <Compile Include="Internal\Object\Subclassing\ObjectSubclassingController.cs" />
     <Compile Include="Internal\ParseCorePlugins.cs" />
     <Compile Include="Internal\ParseDecoder.cs" />
     <Compile Include="Internal\ParseEncoder.cs" />

Parse/Parse.Unity.csproj

@@ -56,6 +56,7 @@
     <Compile Include="Compat\Progress.cs" />
     <Compile Include="Compat\ThreadLocal.cs" />
     <Compile Include="Compat\Tuple.cs" />
+    <Compile Include="Compat\Type.cs" />
     <Compile Include="Internal\Analytics\Controller\IParseAnalyticsController.cs" />
     <Compile Include="Internal\Analytics\Controller\ParseAnalyticsController.cs" />
     <Compile Include="Internal\Cloud\Controller\IParseCloudCodeController.cs" />
@@ -90,6 +91,9 @@
     <Compile Include="Internal\Object\Controller\ParseObjectController.cs" />
     <Compile Include="Internal\Object\State\IObjectState.cs" />
     <Compile Include="Internal\Object\State\MutableObjectState.cs" />
+    <Compile Include="Internal\Object\Subclassing\IObjectSubclassingController.cs" />
+    <Compile Include="Internal\Object\Subclassing\ObjectSubclassInfo.cs" />
+    <Compile Include="Internal\Object\Subclassing\ObjectSubclassingController.cs" />
     <Compile Include="Internal\ParseAddOperation.cs" />
     <Compile Include="Internal\ParseAddUniqueOperation.cs" />
     <Compile Include="Internal\ParseCorePlugins.cs" />

Parse/Parse.csproj

@@ -66,6 +66,9 @@
     <Compile Include="Internal\Object\Controller\ParseObjectController.cs" />
     <Compile Include="Internal\Object\State\IObjectState.cs" />
     <Compile Include="Internal\Object\State\MutableObjectState.cs" />
+    <Compile Include="Internal\Object\Subclassing\IObjectSubclassingController.cs" />
+    <Compile Include="Internal\Object\Subclassing\ObjectSubclassInfo.cs" />
+    <Compile Include="Internal\Object\Subclassing\ObjectSubclassingController.cs" />
     <Compile Include="Internal\ParseAddOperation.cs" />
     <Compile Include="Internal\ParseAddUniqueOperation.cs" />
     <Compile Include="Internal\Analytics\Controller\IParseAnalyticsController.cs" />

Parse/Parse.iOS.csproj

@@ -136,6 +136,9 @@
     <Compile Include="Internal\Object\Controller\ParseObjectController.cs" />
     <Compile Include="Internal\Object\State\IObjectState.cs" />
     <Compile Include="Internal\Object\State\MutableObjectState.cs" />
+    <Compile Include="Internal\Object\Subclassing\IObjectSubclassingController.cs" />
+    <Compile Include="Internal\Object\Subclassing\ObjectSubclassInfo.cs" />
+    <Compile Include="Internal\Object\Subclassing\ObjectSubclassingController.cs" />
     <Compile Include="Internal\ParseAddOperation.cs" />
     <Compile Include="Internal\ParseAddUniqueOperation.cs" />
     <Compile Include="Internal\ParseCorePlugins.cs" />