require 'win32ole'

class SqlServer
    # This class manages database connection and queries
    attr_accessor :connection, :data, :fields
    attr_writer :username, :password

    def initialize(host, username = 'sa', password='')
        @connection = nil
        @data = nil
    @host = host
    @username = username
    @password = password
    end

    def open(database)
        # Open ADO connection to the SQL Server database
        connection_string =  "Provider=SQLOLEDB.1;"
        connection_string << "Persist Security Info=False;"
        connection_string << "User ID=#{@username};"
        connection_string << "password=#{@password};"
        connection_string << "Initial Catalog=#{database};"
        connection_string << "Data Source=#{@host};"
        connection_string << "Network Library=dbmssocn"
        @connection = WIN32OLE.new('ADODB.Connection')
        @connection.Open(connection_string)
    end

    def query(sql)
        # Create an instance of an ADO Recordset
        recordset = WIN32OLE.new('ADODB.Recordset')
        # Open the recordset, using an SQL statement and the
        # existing ADO connection
        recordset.Open(sql, @connection)
        # Create and populate an array of field names
        @fields = []
        recordset.Fields.each do |field|
            @fields << field.Name
        end
        begin
            # Move to the first record/row, if any exist
            recordset.MoveFirst
            # Grab all records
            @data = recordset.GetRows
        rescue
            @data = []
        end
        recordset.Close
        # An ADO Recordset's GetRows method returns an array 
        # of columns, so we'll use the transpose method to 
        # convert it to an array of rows
        @data = @data.transpose
    end

    def add_person
        puts "Enter groupname:"
        groupname = gets.chomp
        puts "Enter username:"
        username = gets.chomp
        puts "Enter loginID:"
        loginID = gets.chomp
        puts "Enter password:"
        password = gets.chomp
        db.execute("INSERT INTO dbo.OtherUser (groupname,username,loginID,password)VALUES(?,?,?,?)",groupname,username,loginID,password)
    end




    def close
        @connection.Close
    end
end

db = SqlServer.new('ryp', 'sa', 'dallasryp123')
db.open('TowerBook')
db.add_person
db.query("select * from TowerBook;")
puts field_names = db.fields
cust = db.data
puts cust.size
puts cust[0].inspect
db.close

脚本如上，可是当使用 add_person 时却发生错误 (如下),请教是哪里的问题

D:/ruby/sql.rb:64:in add_person': undefined local variable or methoddb' for # SqlServer:0x2944e18 (NameError) from D:/ruby/sql.rb:77:in `