Ensure connection open for OE queries and fix connection disposal (#359)

* Ensure connection open for OE queries and fix connection disposal
- Dispose connection in Metadata service, to ensure we cleanly dispose and don't rely on garbage colleciton
- Fixed issue where if the connection was closed, expanding databases in the Server would fail. This is because SMO doesn't always reopen the connection, certainly not for Server level queries. The solution is to always check if open and reopen.
- Added unit tests for this, which required mocking the relevant IsOpen / OpenConnection methods. Refactored SMO wrapper calls into a dedicated class file to handle this

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

@@ -7,9 +7,11 @@ using System;
 using System.Collections;
 using System.Collections.Generic;
 using System.Globalization;
+using Microsoft.SqlServer.Management.Common;
 using Microsoft.SqlServer.Management.Smo;
 using Microsoft.SqlTools.Extensibility;
 using Microsoft.SqlTools.ServiceLayer.ObjectExplorer.Nodes;
+using Microsoft.SqlTools.Utility;
 
 namespace Microsoft.SqlTools.ServiceLayer.ObjectExplorer.SmoModel
 {
@@ -18,14 +20,25 @@ namespace Microsoft.SqlTools.ServiceLayer.ObjectExplorer.SmoModel
     /// </summary>
     public class SmoQueryContext
     {
+        private Server server;
+        private Database database;
+        private SmoObjectBase parent;
+        private SmoWrapper smoWrapper;
+
         /// <summary>
         /// Creates a context object with a server to use as the basis for any queries
         /// </summary>
         /// <param name="server"></param>
         public SmoQueryContext(Server server, IMultiServiceProvider serviceProvider)
+            : this(server, serviceProvider, null)
         {
-            Server = server;
+        }
+
+        internal SmoQueryContext(Server server, IMultiServiceProvider serviceProvider, SmoWrapper serverManager)
+        {
+            this.server = server;
             ServiceProvider = serviceProvider;
+            this.smoWrapper = serverManager ?? new SmoWrapper();
         }
 
         /// <summary>
@@ -36,17 +49,40 @@ namespace Microsoft.SqlTools.ServiceLayer.ObjectExplorer.SmoModel
         /// <summary>
         /// The server SMO will query against
         /// </summary>
-        public Server Server { get; private set; }
+        public Server Server { 
+            get
+            {
+                return GetObjectWithOpenedConnection(server);
+            } 
+        }
 
         /// <summary>
         /// Optional Database context object to query against
         /// </summary>
-        public Database Database { get; set; }
+        public Database Database { 
+            get
+            {
+                return GetObjectWithOpenedConnection(database);
+            }
+            set
+            {
+                database = value;
+            }
+        }
 
         /// <summary>
         /// Parent of a give node to use for queries
         /// </summary>
-        public SmoObjectBase Parent { get; set; }
+        public SmoObjectBase Parent { 
+            get
+            {
+                return GetObjectWithOpenedConnection(parent);
+            }
+            set
+            {
+                parent = value;
+            }
+        }
 
         /// <summary>
         /// A query loader that can be used to find <see cref="SmoQuerier"/> objects
@@ -89,6 +125,7 @@ namespace Microsoft.SqlTools.ServiceLayer.ObjectExplorer.SmoModel
 
             return service;
         }
+
         /// <summary>
         /// Copies the context for use by another node
         /// </summary>
@@ -96,13 +133,39 @@ namespace Microsoft.SqlTools.ServiceLayer.ObjectExplorer.SmoModel
         /// <returns>new <see cref="SmoQueryContext"/> with all fields except <see cref="Parent"/> the same</returns>
         public SmoQueryContext CopyWithParent(SmoObjectBase parent)
         {
-            SmoQueryContext context = new SmoQueryContext(this.Server, this.ServiceProvider)
+            SmoQueryContext context = new SmoQueryContext(this.Server, this.ServiceProvider, this.smoWrapper)
             {
-                Database = this.Database,
+                database = this.Database,
                 Parent = parent,
                 SqlServerType = this.SqlServerType
             };
             return context;
         }
+
+        private T GetObjectWithOpenedConnection<T>(T smoObj)
+            where T : SmoObjectBase
+        {
+            if (smoObj != null)
+            {
+                EnsureConnectionOpen(smoObj);
+            }
+            return smoObj;
+        }
+
+        /// <summary>
+        /// Ensures the server objects connection context is open. This is used by all child objects, and 
+        /// the only way to easily access is via the server object. This should be called during access of
+        /// any of the object properties
+        /// </summary>
+        private void EnsureConnectionOpen(SmoObjectBase smoObj)
+        {
+            if (!smoWrapper.IsConnectionOpen(smoObj))
+            {
+                // We have a closed server connection. Reopen this
+                // Note: not currently catching connection exceptions. Expect this to bubble
+                // up to calling methods and be logged there as this would be happening there in any case
+                smoWrapper.OpenConnection(smoObj);
+            }
+        }
     }
 }