关于VB连接数据库的问题
来源:百度知道 编辑:UC知道 时间:2024/05/24 08:44:17
在模块的代码::
Option Explicit
Public Conn As New ADODB.Connection
Public Rs As ADODB.Recordset
Public Sql As String
Public Function LandMDB(ByVal vFile As String) As String
On Error Resume Next
Sql = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" & vFile & ";Persist Security Info=False"
Conn.Open Sql
If Err <> 0 Then LandMDB = "连接数据库错误,请检查[ " & vFile & " ]是否存在。"
End Function
要窗体的代码:
Private Sub Form_Load()
Dim ErrInfo As String
ErrInfo = LandMDB(App.Path & "\db1.mdb")
If Len(ErrInfo) <> 0 Then MsgBox ErrInfo, vbOKOnly + vbCritical, "载入数据库错误"
Set Rs = New ADODB.Recordset
Sql = "select 数据.学号,数据.姓名,数据.sex,数据.mz,数据.jg,数据.ymd,数据.age,数据.zy,point.xh from 数据,point where 数据.姓名=point.name"
Rs.Open Sql, Conn, 1, 3
End Sub
我看不懂Len(Err
Option Explicit
Public Conn As New ADODB.Connection
Public Rs As ADODB.Recordset
Public Sql As String
Public Function LandMDB(ByVal vFile As String) As String
On Error Resume Next
Sql = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" & vFile & ";Persist Security Info=False"
Conn.Open Sql
If Err <> 0 Then LandMDB = "连接数据库错误,请检查[ " & vFile & " ]是否存在。"
End Function
要窗体的代码:
Private Sub Form_Load()
Dim ErrInfo As String
ErrInfo = LandMDB(App.Path & "\db1.mdb")
If Len(ErrInfo) <> 0 Then MsgBox ErrInfo, vbOKOnly + vbCritical, "载入数据库错误"
Set Rs = New ADODB.Recordset
Sql = "select 数据.学号,数据.姓名,数据.sex,数据.mz,数据.jg,数据.ymd,数据.age,数据.zy,point.xh from 数据,point where 数据.姓名=point.name"
Rs.Open Sql, Conn, 1, 3
End Sub
我看不懂Len(Err
LandMDB()是你自定义的函数,它的返回值是“LandMDB”
在数据库链接成功时,没有返回值,那么“LandMDB(App.Path & "\db1.mdb") ”是空值,这样“ErrInfo ="" ”,那么“Len(ErrInfo)”=0了,就不会发生数据库载入错误了;
相反,如果数据库链接不成功,函数就会产生错误,这时“LandMDB(App.Path & "\db1.mdb")”的返回值是“连接数据库错误,请检查[ App.Path & "\db1.mdb" ]是否存在”,那么“Len(ErrInfo)”<>0了,就会发生数据库载入错误,并且用提示框提示你:错误类型
Public Function LandMDB(ByVal vFile As String) As String
On Error Resume Next
Sql = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" & vFile & ";Persist Security Info=False"
Conn.Open Sql
If Err <> 0 Then LandMDB = "连接数据库错误,请检查[ " & vFile & " ]是否存在。"
End Function
如果连接发生错误,返回
"连接数据库错误,请检查[ " & vFile & " ]是否存在。"
正确返回空字符