From 755a7ea44649cc1137e415632babccef0f1aec2f Mon Sep 17 00:00:00 2001
From: Red Forks <redforks@gmail.com>
Date: Tue, 26 Jul 2011 14:41:17 +0800
Subject: [PATCH] add dropTarget arg to RenameCollection()

if database has collection named with `newCollectionName', drop it
before rename in atomic way.
---
 Driver/Core/MongoDatabase.cs                 | 11 ++++++++---
 DriverOnlineTests/Core/MongoDatabaseTests.cs | 18 ++++++++++++++++++
 2 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/Driver/Core/MongoDatabase.cs b/Driver/Core/MongoDatabase.cs
index 87608f515b..c870722c9e 100644
--- a/Driver/Core/MongoDatabase.cs
+++ b/Driver/Core/MongoDatabase.cs
@@ -726,16 +726,21 @@ namespace MongoDB.Driver {
         /// Renames a collection on this database.
         /// </summary>
         /// <param name="oldCollectionName">The old name for the collection.</param>
-        /// <param name="newCollectionName">The new name for the collection.</param>
+        /// <param name="newCollectionName">The new name for the collection.</param>
+        /// <param name="dropTarget">drop target collection if exist in db</param>
         /// <returns>A CommandResult.</returns>
         public virtual CommandResult RenameCollection(
             string oldCollectionName,
-            string newCollectionName
+            string newCollectionName,
+            bool dropTarget = false
         ) {
             var command = new CommandDocument {
                 { "renameCollection", string.Format("{0}.{1}", name, oldCollectionName) },
                 { "to", string.Format("{0}.{1}", name, newCollectionName) }
-            };
+            };
+            if (dropTarget) {
+              command.Add("dropTarget", BsonBoolean.True);
+            }
             return server.RunAdminCommand(command);
         }
 
diff --git a/DriverOnlineTests/Core/MongoDatabaseTests.cs b/DriverOnlineTests/Core/MongoDatabaseTests.cs
index b1da39b293..1de3ca393b 100644
--- a/DriverOnlineTests/Core/MongoDatabaseTests.cs
+++ b/DriverOnlineTests/Core/MongoDatabaseTests.cs
@@ -162,6 +162,24 @@ namespace MongoDB.DriverOnlineTests {
             Assert.IsTrue(database.CollectionExists(collectionName2));
         }
 
+        [Test]
+        public void TestRenameCollectionDropTarget() {
+            const string collectionName1 = "testrenamecollection3";
+            const string collectionName2 = "testrenamecollection4";
+            Assert.IsFalse(database.CollectionExists(collectionName1));
+            Assert.IsFalse(database.CollectionExists(collectionName2));
+
+            database[collectionName1].Insert(new BsonDocument());
+            database[collectionName2].Insert(new BsonDocument());
+            Assert.IsTrue(database.CollectionExists(collectionName1));
+            Assert.True(database.CollectionExists(collectionName2));
+
+            Assert.Throws(typeof(MongoCommandException), () => database.RenameCollection(collectionName1, collectionName2));
+            database.RenameCollection(collectionName1, collectionName2, true);
+            Assert.IsFalse(database.CollectionExists(collectionName1));
+            Assert.IsTrue(database.CollectionExists(collectionName2));
+        }
+
         [Test]
         public void TestUserMethods() {
             var collection = database["system.users"];