Async: messages and doc tags (#379)

Author: AlekseyMartynov

net/DevExtreme.AspNet.Data/Async/ReflectionAsyncAdapter.cs

@@ -34,7 +34,7 @@ MethodInfo GetCountAsyncMethod() {
                 if(IsXPO)
                     return XpoMethods.CountAsyncMethod;
 
-                throw NotSupported();
+                throw ProviderNotSupported(provider);
             }
 
             return InvokeCountAsync(GetCountAsyncMethod(), provider, expr, cancellationToken);
@@ -53,12 +53,18 @@ public Task<IEnumerable<T>> ToEnumerableAsync<T>(IQueryProvider provider, Expres
             if(IsXPO)
                 return InvokeToArrayAsync<T>(XpoMethods.ToArrayAsyncMethod, provider, expr, cancellationToken);
 
-            throw NotSupported();
+            throw ProviderNotSupported(provider);
         }
 
-        static Exception NotSupported() {
-#warning TODO message
-            throw new NotSupportedException();
+        static Exception ProviderNotSupported(IQueryProvider provider) {
+            var providerType = provider.GetType();
+            if(providerType.IsGenericType)
+                providerType = providerType.GetGenericTypeDefinition();
+
+            var message = $"Async operations for the LINQ provider '{providerType.FullName}' are not supported."
+                + $" You can implement a custom async adapter ({typeof(IAsyncAdapter).FullName}) and register it via '{typeof(CustomAsyncAdapters).FullName}.{nameof(CustomAsyncAdapters.RegisterAdapter)}'.";
+
+            return new NotSupportedException(message);
         }
 
         static class EF6Methods {

net/DevExtreme.AspNet.Data/DataSourceLoader.cs

@@ -8,32 +8,44 @@
 namespace DevExtreme.AspNet.Data {
 
     /// <summary>
-    /// Provides static methods for loading data from collections that implement the IEnumerable&lt;T&gt; or IQueryable&lt;T&gt; interface.
+    /// Provides static methods for loading data from collections that implement the
+    /// <see cref="System.Collections.Generic.IEnumerable{T}"/> or <see cref="System.Linq.IQueryable{T}"/> interface.
     /// </summary>
     public class DataSourceLoader {
 
         /// <summary>
-        /// Loads data from a collection that implements the IEnumerable&lt;T&gt; interface.
+        /// Loads data from a collection that implements the <see cref="System.Collections.Generic.IEnumerable{T}"/> interface.
         /// </summary>
         /// <typeparam name="T">The type of objects in the collection.</typeparam>
-        /// <param name="source">A collection that implements the IEnumerable&lt;T&gt; interface.</param>
+        /// <param name="source">A collection that implements the <see cref="System.Collections.Generic.IEnumerable{T}"/> interface.</param>
         /// <param name="options">Data processing settings when loading data.</param>
         /// <returns>The load result.</returns>
         public static LoadResult Load<T>(IEnumerable<T> source, DataSourceLoadOptionsBase options) {
             return Load(source.AsQueryable(), options);
         }
 
         /// <summary>
-        /// Loads data from a collection that implements the IQueryable&lt;T&gt; interface.
+        /// Loads data from a collection that implements the <see cref="System.Linq.IQueryable{T}"/> interface.
         /// </summary>
         /// <typeparam name="T">The type of objects in the collection.</typeparam>
-        /// <param name="source">A collection that implements the IQueryable&lt;T&gt; interface.</param>
+        /// <param name="source">A collection that implements the <see cref="System.Linq.IQueryable{T}"/> interface.</param>
         /// <param name="options">Data processing settings when loading data.</param>
         /// <returns>The load result.</returns>
         public static LoadResult Load<T>(IQueryable<T> source, DataSourceLoadOptionsBase options) {
             return LoadAsync(source, options, CancellationToken.None, true).GetAwaiter().GetResult();
         }
 
+        /// <summary>
+        /// Asynchronously loads data from a collection that implements the <see cref="System.Linq.IQueryable{T}"/> interface.
+        /// </summary>
+        /// <typeparam name="T">The type of objects in the collection.</typeparam>
+        /// <param name="source">A collection that implements the <see cref="System.Linq.IQueryable{T}"/> interface.</param>
+        /// <param name="options">Data processing settings when loading data.</param>
+        /// <param name="cancellationToken">A <see cref="System.Threading.CancellationToken"/> object that delivers a cancellation notice to the running operation.</param>
+        /// <returns>
+        /// A <see cref="System.Threading.Tasks.Task{TResult}"/> object that represents the asynchronous operation.
+        /// The task result contains the load result.
+        /// </returns>
         public static Task<LoadResult> LoadAsync<T>(IQueryable<T> source, DataSourceLoadOptionsBase options, CancellationToken cancellationToken = default(CancellationToken)) {
             return LoadAsync(source, options, cancellationToken, false);
         }