Sqlhelper.ExecuteReader关闭connection的方式

 刚下载了Microsoft.ApplicationBlocks.Data看了看，了解了Sqlhelper.ExecuteReader返回的datareader是如何关闭的。
首先在SqlHelper类中有个枚举类型的变量SqlConnectionOwnership，它有两个值Internal，External； 用来指示connection的关闭方式。当传给ExecuteReader的参数为External时（由外部调用者传入connection），connection由调用者关闭，否则cmd.ExecuteReader(CommandBehavior.CloseConnection),即在调用command的ExecuteReader时设置为关闭datareader的时候同时自动关闭connection.
相关代码如下：

       /**/ /// <summary>
        /// This enum is used to indicate whether the connection was provided by the caller, or created by SqlHelper, so that
        /// we can set the appropriate CommandBehavior when calling ExecuteReader()
        /// </summary>
         private   enum  SqlConnectionOwnership    
         {
            /**//// <summary>Connection is owned and managed by SqlHelper</summary>
            Internal, 
            /**//// <summary>Connection is owned and managed by the caller</summary>
            External
        }
/**/ //////////////////

         private   static  SqlDataReader ExecuteReader(SqlConnection connection, SqlTransaction transaction, CommandType commandType,  string  commandText, SqlParameter[] commandParameters, SqlConnectionOwnership connectionOwnership)
         {    
            if( connection == null ) throw new ArgumentNullException( "connection" );
            bool mustCloseConnection = false;
            // Create a command and prepare it for execution
            SqlCommand cmd = new SqlCommand();
            try
            {
                PrepareCommand(cmd, connection, transaction, commandType, commandText, commandParameters, out mustCloseConnection );
                  // Create a reader
                SqlDataReader dataReader;

                // Call ExecuteReader with the appropriate Command Behavior
                if (connectionOwnership == SqlConnectionOwnership.External)
                {
                    dataReader = cmd.ExecuteReader();
                }
                else
                {
                    dataReader = cmd.ExecuteReader(CommandBehavior.CloseConnection);
                }
                bool canClear = true;
                foreach(SqlParameter commandParameter in cmd.Parameters)
                {
                    if (commandParameter.Direction != ParameterDirection.Input)
                        canClear = false;
                }
            
                if (canClear)
                {
                    cmd.Parameters.Clear();
                }

                return dataReader;
            }
            catch
            {
                if( mustCloseConnection )
                    connection.Close();
                throw;
            }
        }