可能平时我们在用vb写程序的过程中，会忽视一些面向对象的思想。希望通过一个例子能够对大家起到抛砖引玉的作用，我们举一个vb访问数据库的例子。这是本人第一次写技术方面的文章，请大家支持！！qq：16644686

1。经常出现的写法

在vb中实现对数据库的访问，我们可能会通过一个全局函数来实现，例如以下的代码：

public function dbsqlopen(strname as string, strpwd as string, _
                            strip as string, strdatabase as string) as adodb.connection
    purpose:   连接sql数据库
    accepts:
               strname-------登陆服务器用户名
               strpwd--------登陆服务器密码
               strip---------服务器地址
               strdatabase---数据库名
    return:    连接对象
    dim madocon as adodb.connection       ///////////////////////////////
    set madocon = new adodb.connection
    madocon.connectionstring = "provider=sqloledb.1;persist security info=false;user id=" _
    & strname & ";pwd=" & strpwd & ";initial catalog=" & strdatabase & ";data source=" & strip & ""
    madocon.open
    set dbsqlopen = madocon
end function

然后在其它地方要用到ado连接的时候就通过该函数来返回。比如:
private sub form_load()
    set rs = new adodb.recordset
    rs.cursortype = adopenkeyset
    rs.locktype = adlockpessimistic
    rs.activeconnection = dbsqlopen(strlocalname, strlocalpwd, "(local)", strlocaldb)
    ........
end sub

程序中如果采用这种方式来实现连接数据库，效率非常的低下。你每用到一次dbsqlopen这个全局函数，全局函数里面声明的adodb.connection就会open一次，假如你的程序频繁调用这个全局函数，可想而之程序的效率将会多么的低下。如何避免这种设计方式呢？我们采用下面的方式。

2.改进的写法

假如我们设计一个类来实现数据库访问就会避免这样的问题。具体代码如下：

private m_adoconn as new adodb.connection
private m_adorecordset as new adodb.recordset

public function dbinit()
    set m_adoconn = nothing
    set m_adorecordset = nothing
end function

public function dbend()
    m_adorecordset.close
    m_adoconn.close
    set m_adorecordset = nothing
    set m_conn = nothing
end function

public function dbsqlopen(strname as string, strpwd as string, _
                            strip as string, strdatabase as string)
    m_adoconn.connectionstring = "provider=sqloledb.1;persist security info=false;user id=" _
    & strname & ";pwd=" & strpwd & ";initial catalog=" & strdatabase & ";data source=" & strip & ""
    m_adoconn.connectiontimeout = 5
    m_adoconn.open
end function

public function dbgetconn() as adodb.connection
    dbgetconn = m_adoconn
end function

我们在模块里面可以声明一个public m_dbclass as dbclass来实现对数据库的访问。

private sub command1_click()
    dim rs1 as adodb.recordset
    rs1.activeconnection = m_dbclass.dbgetconn
end sub

private sub form_load()
    dim strname as string
    dim strpwd as string
    dim strip as string
    dim strdatabase as string
   
    strname = "sa"
    strpwd = ""
    strip = "192.168.0.37"
    strdatabase = ""
   
    m_dbclass.dbinit
    m_dbclass.dbsqlopen strname, strpwd, strip, strdatabase
end sub

private sub form_unload(cancel as integer)
    m_dbclass.dbend
end sub

每一次要用到数据库连接的时候我们就通过类里面的dbgetconn方法来返回一个adodb.connection。