Object Explorer Service (#311)

* moving OE service from an old branch

src/Microsoft.SqlTools.ServiceLayer/ObjectExplorer/SmoModel/SmoQuerier.cs

@@ -0,0 +1,42 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using System;
+using System.Collections.Generic;
+using Microsoft.SqlServer.Management.Smo;
+using Microsoft.SqlTools.Extensibility;
+
+namespace Microsoft.SqlTools.ServiceLayer.ObjectExplorer.SmoModel
+{
+    /// <summary>
+    /// A <see cref="SmoQuerier"/> handles SMO queries for one or more SMO object types.
+    /// The <see cref="SupportedObjectTypes"/> property defines which types can be queried.
+    /// 
+    /// To query multiple 
+    /// </summary>
+    public abstract class SmoQuerier : IComposableService
+    {
+        public abstract Type[] SupportedObjectTypes { get;  }
+        
+        /// <summary>
+        /// Queries SMO for a collection of objects using the <see cref="SmoQueryContext"/> 
+        /// </summary>
+        /// <param name="context"></param>
+        /// <returns></returns>
+        public abstract IEnumerable<SqlSmoObject> Query(SmoQueryContext context);
+
+        internal IMultiServiceProvider ServiceProvider
+        {
+            get;
+            private set;
+        }
+
+        public void SetServiceProvider(IMultiServiceProvider provider)
+        {
+            ServiceProvider = provider;
+        }
+    }
+    
+}