背景介绍：
数据库中的T_Line_Info表中存放着学生上机的记录，也就是我们需要查询上机记录的表，其中具体内容为：
界面设计如下：
右击DataGridView控件，选择编辑列，设计它的列名。
代码实现部分：
U层：
Public Class frmQueryOnRecord
Private Sub btn_Query_Click(sender As Object, e As EventArgs) Handles btn_Query.Click
Dim student As New Login.Model.LineInfo
Dim BUser As New Login.BLL.LoginManager
‘将输入的卡号传给实体
student.cardno = txtcardno.Text
DataGridView1.Visible = True
‘在数据库中查到该卡号的上机信息
Dim uTable = BUser.QueryOnRecord(student)
If uTable.Rows.Count > 0 Then
‘将数据显示在DataGridView中
DataGridView1.Item(1, DataGridView1.NewRowIndex).Value = uTable.Rows(0)("studentname")
DataGridView1.Item(2, DataGridView1.NewRowIndex).Value = uTable.Rows(0)("ondate")
DataGridView1.Item(3, DataGridView1.NewRowIndex).Value = uTable.Rows(0)("ontime")
DataGridView1.Item(4, DataGridView1.NewRowIndex).Value = uTable.Rows(0)("offdate")
DataGridView1.Item(5, DataGridView1.NewRowIndex).Value = uTable.Rows(0)("ontime")
DataGridView1.Item(6, DataGridView1.NewRowIndex).Value = uTable.Rows(0)("moeny")
DataGridView1.Item(7, DataGridView1.NewRowIndex).Value = uTable.Rows(0)("consumemoney")
Else
‘没有查到内容时
DataGridView1.Rows.Clear()
MsgBox("没有找到记录！")
End If
End Sub
End Class
B层：
Public Function QueryOnRecord(student As Login.Model.LineInfo) As DataTable
Dim f As New DFactory.DBFactory
Dim istudent As Login.Interface.ILineInfo
istudent = f.QueryOnlineInfo
‘接收DataTable
Table = istudent.Query_OnRecord(student)
‘把Table返回到U层
Return Table
End Function
接口：
Public Interface ILineInfo
‘返回的类型是DataTable
Function Query_OnRecord(student As Login.Model.LineInfo) As DataTable
End Interface
实体：
Public Class LineInfo
‘与上机记录表中的字段一一对应
Public cardno As String
Public studentname As String
Public ondate As String
Public ontime As String
Public offdate As String
Public offtime As String
Public money As String
Public consumemoeny As String
End Class
sqlHelper中的GetDataTable方法
Public Function GetDataTable(ByVal cmdTxt As String, ByVal cmdType As CommandType, ByVal paras As SqlParameter()) As DataTable
Dim strConnStr As String = System.Configuration.ConfigurationManager.AppSettings("ConnStr")
‘定义一个数据库连接对象
Dim conn As SqlConnection = New SqlConnection(strConnStr)
Dim cmd As New SqlCommand ‘定义一个命令对象
Dim adataset As DataSet
Dim adaptor As SqlDataAdapter ‘定义一个适配器对象
cmd = New SqlCommand(cmdTxt, conn)
adaptor = New SqlDataAdapter(cmd)
adataset = New DataSet
cmd.CommandType = cmdType
cmd.Parameters.AddRange(paras)
Try
‘打开数据库连接
If conn.State = ConnectionState.Closed Then
conn.Open()
End If
‘填充数据集
adaptor.Fill(adataset)
Return adataset.Tables(0)
Catch ex As Exception
MsgBox(ex.Message, , "数据库操作")
Finally
‘关闭数据库连接
If conn.State = ConnectionState.Open Then
conn.Close()
End If
End Try
End Function
D层：
Public Function QueryOnRecord(student As Login.Model.LineInfo) As DataTable Implements ILineInfo.Query_OnRecord
‘按卡号在上机记录表中查找
Dim sql As String = "select * from T_Line_Info where cardno=" & student.cardno
Dim cmd As SqlCommand = New SqlCommand(sql, conn)
Dim helper As New Login.DAL.sqlHelper
‘设置参数
Dim paras As SqlParameter() = {New SqlParameter("@cardno", student.cardno)}
Try
conn.Open()
‘调用sqlhelper中的GetDataTable方法
Return helper.GetDataTable(sql, CommandType.Text, paras)
Catch ex As Exception
MsgBox(ex.Message, "")
End Try
End Function
运行结果：