如果在数据库中循环 table，则为重复输入或输出发出错误消息
Making an error message for the repeating in or out if loops in the database table
美好的一天，为了清楚起见，我将介绍我正在进行的系统 "Gate attendance for student in our university"，该系统由 RFID reader RC522 和 Arduino 组成，学生应该点击 his/her RFID 标签和检索到的数据显示在监视器上。该系统是我们的顶峰项目，它已经完成，但面板需要我们解决另一个问题。
扫码、取资料、注册学生的功能都已经搞定了，这适用于大学生，可以随意出门，随时看时间安排，不像高中一进一出。
这两个RFID reader被放置在大学的入口和出口那里有一个系统用于out in exit和In for the entrance.The 从in和out检索的数据将保存到同一个系统中table。
如果他在没有先出去的情况下点击进入，我该如何向学生显示消息框警告？我对查询有所了解。但我不知道。我的 Capstone 需要一些帮助。提前感谢任何评论和建议。这是我的代码，用于根据文本框更改事件中显示的 RFID 标签编号检索数据。顺便说一下，我的 table studlogs 是处理出勤的人。
Private Sub studtag_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles studtag.TextChanged
Notenrolled.Close()
greet.Text = ""
PictureBox4.Visible = False
If studtag.Text = "44F2F38B" Then
Endday()
End If
If studtag.Text = recents.Text Then
Alreadylogin.Show()
ElseIf studtag.TextLength = 8 Then
DataGridView1.Sort(DataGridView1.Columns(6), System.ComponentModel.ListSortDirection.Descending)
con = New MySqlConnection
con.ConnectionString = "server=localhost;userid=root;password=1234;database=dat"
Dim query As String
query = "select * from dat.students"
cmd = New MySqlCommand(query, con)
Dim table As New DataTable
Try
con.Open()
'Gets or sets an SQL statement or stored procedure used to select records in the database.
With cmd
.Connection = con
.CommandText = "SELECT * from students where `studtags`='" & studtag.Text & "';"
End With
da.SelectCommand = cmd
da.Fill(table)
'it gets the data from specific column and fill it into Label
idno.Text = table.Rows(0).Item(1)
lastxt.Text = table.Rows(0).Item(2)
firstxt.Text = table.Rows(0).Item(3)
middletxt.Text = table.Rows(0).Item(4)
dob.Text = table.Rows(0).Item(6)
year.Text = table.Rows(0).Item(7)
crsetxt.Text = table.Rows(0).Item(10)
tagtxt.Text = studtag.Text
timein.Text = times.Text
dr = cmd.ExecuteReader()
dr.Read()
If dob.Text = bday.Text Then
greet.Text = firstxt.Text + " Today is your Birthday. Greetings :D."
PictureBox4.Visible = True
End If
Dim img() As Byte = CType(dr("studpic"), Byte())
Using ms As New IO.MemoryStream(img)
PictureBox1.Image = Image.FromStream(ms)
End Using
My.Computer.Audio.Play("C:\Users\BOR\Desktop\Parsu Gate\Parsu\audio\scanned.wav")
insert()
loadtable()
studdailyhistory()
Catch ex As Exception
Notenrolled.Show()
DataGridView1.Sort(DataGridView1.Columns(5), System.ComponentModel.ListSortDirection.Descending)
If studtag.Text = "44F2F38B" Then
Notenrolled.Close()
End If
Finally
con.Dispose()
con.Close()
End Try
End If
recents.Text = tagtxt.Text
End Sub
Public Sub insert()
con = New MySqlConnection
con.ConnectionString = "server=localhost;userid=root;password=1234;database=dat"
Dim reader As MySqlDataReader
Dim mstream As New System.IO.MemoryStream()
Dim arrImage() As Byte = mstream.GetBuffer()
mstream.Close()
Try
con.Open()
Dim query3 As String
query3 = "insert into dat.studlogs (studtags,idno,lastxt,firstxt,middletxt,dob,log,timein,crse,studpic) values ('" & tagtxt.Text & "','" & idno.Text & "','" & lastxt.Text & "','" & firstxt.Text & "','" & middletxt.Text & "','" & dob.Text & "','" & log.Text & "','" & timein.Text & "','" & crsetxt.Text & "',@studpic)"
cmd = New MySqlCommand(query3, con)
cmd.Parameters.AddWithValue("@studpic", arrImage)
reader = cmd.ExecuteReader
con.Close()
Catch ex As Exception
MessageBox.Show(ex.Message)
Finally
con.Dispose()
End Try
End Sub
Public Sub studdailyhistory()
con = New MySqlConnection
con.ConnectionString = "server=localhost;userid=root;password=1234;database=dat"
Dim reader As MySqlDataReader
Dim mstream As New System.IO.MemoryStream()
Dim arrImage() As Byte = mstream.GetBuffer()
mstream.Close()
Try
con.Open()
Dim query3 As String
query3 = "insert into dat.studdailyhistory (studtags,idno,lastxt,firstxt,middletxt,dob,log,timein,crse,dates,studpic) values ('" & tagtxt.Text & "','" & idno.Text & "','" & lastxt.Text & "','" & firstxt.Text & "','" & middletxt.Text & "','" & dob.Text & "','" & log.Text & "','" & timein.Text & "','" & crsetxt.Text & "','" & wholedate.Text & "',@studpic)"
cmd = New MySqlCommand(query3, con)
cmd.Parameters.AddWithValue("@studpic", arrImage)
reader = cmd.ExecuteReader
con.Close()
Catch ex As Exception
MessageBox.Show(ex.Message)
Finally
con.Dispose()
End Try
End Sub
Public Sub loadtable()
con = New MySqlConnection
con.ConnectionString = "server=localhost;userid=root;password=1234;database=dat"
Dim SDA As New MySqlDataAdapter
Dim dbDataset As New DataTable
Dim bSource As New BindingSource
Try
con.Open()
Dim query3 As String
query3 = "select idno as 'Student_ID',lastxt as 'LastName',firstxt as 'FirstName',middletxt as 'MiddleName',log as 'Status',timein as 'Timein',crse as 'Course' from dat.studlogs"
cmd = New MySqlCommand(query3, con)
SDA.SelectCommand = cmd
SDA.Fill(dbDataset)
bSource.DataSource = dbDataset
DataGridView1.DataSource = bSource
SDA.Update(dbDataset)
DataGridView1.Sort(DataGridView1.Columns(5), System.ComponentModel.ListSortDirection.Descending)
If dbDataset.Rows.Count > 0 Then
logins.Text = dbDataset.Rows.Count.ToString()
End If
con.Close()
Catch ex As Exception
MessageBox.Show(ex.Message)
Finally
con.Dispose()
End Try
End Sub
我不确定我是否理解正确，但我想你不希望学生能够在没有下班的情况下打卡两次。
你有多种选择。
最简单的，您可以在数据库中使用状态字段。当学生打卡时，然后保存 "status"=1（学生在场），并在打卡时 "status"=0（学生不在场）。在每次上下班打卡时，您都会检查学生的状态。如果 1 则不能再次打卡，因为 she/he 已经在现场了。
或者，当他们点击钥匙扣时，您保存在日志中，这是一个入口或离开，当您向学生查询 table 时，您按上次插入时间订购 table，这样最后一条记录就会出现在您的位置查看日志的最后状态。
编辑：
在数据库中为学生 table 添加一个额外的 bool 类型列，例如 "studOnsite" 并设置默认值 0。当学生扫描卡片时，您可以从 table 此处获取学生详细信息：
.CommandText = "SELECT * from students where `studtags`='" & studtag.Text & "';"
您还将取回 "studOnsite" 列。在您可以简单地检查值之后：
if (table.Rows(0).Item("studOnsite") then
'student already onsite so she/he is leaving
greet.Text = firstxt.Text & "Good bye!"
'update the student table and change "studOnsite" to false
'dim query as string=string.format("UPDATE students SET studOnsite=false WHERE studtags='{0}'",studtag.Text)
else
'student wasn't onsite so she/he is just arrived
greet.Text = firstxt.Text & "Welcome back!"
'update the student table and change "studOnsite" to true as student is onsite now
'dim query as string=string.format("UPDATE students SET studOnsite=true WHERE studtags='{0}'",studtag.Text)
end if
美好的一天，为了清楚起见，我将介绍我正在进行的系统 "Gate attendance for student in our university"，该系统由 RFID reader RC522 和 Arduino 组成，学生应该点击 his/her RFID 标签和检索到的数据显示在监视器上。该系统是我们的顶峰项目，它已经完成，但面板需要我们解决另一个问题。
扫码、取资料、注册学生的功能都已经搞定了，这适用于大学生，可以随意出门，随时看时间安排，不像高中一进一出。
这两个RFID reader被放置在大学的入口和出口那里有一个系统用于out in exit和In for the entrance.The 从in和out检索的数据将保存到同一个系统中table。 如果他在没有先出去的情况下点击进入，我该如何向学生显示消息框警告？我对查询有所了解。但我不知道。我的 Capstone 需要一些帮助。提前感谢任何评论和建议。这是我的代码，用于根据文本框更改事件中显示的 RFID 标签编号检索数据。顺便说一下，我的 table studlogs 是处理出勤的人。
Private Sub studtag_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles studtag.TextChanged
Notenrolled.Close()
greet.Text = ""
PictureBox4.Visible = False
If studtag.Text = "44F2F38B" Then
Endday()
End If
If studtag.Text = recents.Text Then
Alreadylogin.Show()
ElseIf studtag.TextLength = 8 Then
DataGridView1.Sort(DataGridView1.Columns(6), System.ComponentModel.ListSortDirection.Descending)
con = New MySqlConnection
con.ConnectionString = "server=localhost;userid=root;password=1234;database=dat"
Dim query As String
query = "select * from dat.students"
cmd = New MySqlCommand(query, con)
Dim table As New DataTable
Try
con.Open()
'Gets or sets an SQL statement or stored procedure used to select records in the database.
With cmd
.Connection = con
.CommandText = "SELECT * from students where `studtags`='" & studtag.Text & "';"
End With
da.SelectCommand = cmd
da.Fill(table)
'it gets the data from specific column and fill it into Label
idno.Text = table.Rows(0).Item(1)
lastxt.Text = table.Rows(0).Item(2)
firstxt.Text = table.Rows(0).Item(3)
middletxt.Text = table.Rows(0).Item(4)
dob.Text = table.Rows(0).Item(6)
year.Text = table.Rows(0).Item(7)
crsetxt.Text = table.Rows(0).Item(10)
tagtxt.Text = studtag.Text
timein.Text = times.Text
dr = cmd.ExecuteReader()
dr.Read()
If dob.Text = bday.Text Then
greet.Text = firstxt.Text + " Today is your Birthday. Greetings :D."
PictureBox4.Visible = True
End If
Dim img() As Byte = CType(dr("studpic"), Byte())
Using ms As New IO.MemoryStream(img)
PictureBox1.Image = Image.FromStream(ms)
End Using
My.Computer.Audio.Play("C:\Users\BOR\Desktop\Parsu Gate\Parsu\audio\scanned.wav")
insert()
loadtable()
studdailyhistory()
Catch ex As Exception
Notenrolled.Show()
DataGridView1.Sort(DataGridView1.Columns(5), System.ComponentModel.ListSortDirection.Descending)
If studtag.Text = "44F2F38B" Then
Notenrolled.Close()
End If
Finally
con.Dispose()
con.Close()
End Try
End If
recents.Text = tagtxt.Text
End Sub
Public Sub insert()
con = New MySqlConnection
con.ConnectionString = "server=localhost;userid=root;password=1234;database=dat"
Dim reader As MySqlDataReader
Dim mstream As New System.IO.MemoryStream()
Dim arrImage() As Byte = mstream.GetBuffer()
mstream.Close()
Try
con.Open()
Dim query3 As String
query3 = "insert into dat.studlogs (studtags,idno,lastxt,firstxt,middletxt,dob,log,timein,crse,studpic) values ('" & tagtxt.Text & "','" & idno.Text & "','" & lastxt.Text & "','" & firstxt.Text & "','" & middletxt.Text & "','" & dob.Text & "','" & log.Text & "','" & timein.Text & "','" & crsetxt.Text & "',@studpic)"
cmd = New MySqlCommand(query3, con)
cmd.Parameters.AddWithValue("@studpic", arrImage)
reader = cmd.ExecuteReader
con.Close()
Catch ex As Exception
MessageBox.Show(ex.Message)
Finally
con.Dispose()
End Try
End Sub
Public Sub studdailyhistory()
con = New MySqlConnection
con.ConnectionString = "server=localhost;userid=root;password=1234;database=dat"
Dim reader As MySqlDataReader
Dim mstream As New System.IO.MemoryStream()
Dim arrImage() As Byte = mstream.GetBuffer()
mstream.Close()
Try
con.Open()
Dim query3 As String
query3 = "insert into dat.studdailyhistory (studtags,idno,lastxt,firstxt,middletxt,dob,log,timein,crse,dates,studpic) values ('" & tagtxt.Text & "','" & idno.Text & "','" & lastxt.Text & "','" & firstxt.Text & "','" & middletxt.Text & "','" & dob.Text & "','" & log.Text & "','" & timein.Text & "','" & crsetxt.Text & "','" & wholedate.Text & "',@studpic)"
cmd = New MySqlCommand(query3, con)
cmd.Parameters.AddWithValue("@studpic", arrImage)
reader = cmd.ExecuteReader
con.Close()
Catch ex As Exception
MessageBox.Show(ex.Message)
Finally
con.Dispose()
End Try
End Sub
Public Sub loadtable()
con = New MySqlConnection
con.ConnectionString = "server=localhost;userid=root;password=1234;database=dat"
Dim SDA As New MySqlDataAdapter
Dim dbDataset As New DataTable
Dim bSource As New BindingSource
Try
con.Open()
Dim query3 As String
query3 = "select idno as 'Student_ID',lastxt as 'LastName',firstxt as 'FirstName',middletxt as 'MiddleName',log as 'Status',timein as 'Timein',crse as 'Course' from dat.studlogs"
cmd = New MySqlCommand(query3, con)
SDA.SelectCommand = cmd
SDA.Fill(dbDataset)
bSource.DataSource = dbDataset
DataGridView1.DataSource = bSource
SDA.Update(dbDataset)
DataGridView1.Sort(DataGridView1.Columns(5), System.ComponentModel.ListSortDirection.Descending)
If dbDataset.Rows.Count > 0 Then
logins.Text = dbDataset.Rows.Count.ToString()
End If
con.Close()
Catch ex As Exception
MessageBox.Show(ex.Message)
Finally
con.Dispose()
End Try
End Sub
我不确定我是否理解正确，但我想你不希望学生能够在没有下班的情况下打卡两次。 你有多种选择。 最简单的，您可以在数据库中使用状态字段。当学生打卡时，然后保存 "status"=1（学生在场），并在打卡时 "status"=0（学生不在场）。在每次上下班打卡时，您都会检查学生的状态。如果 1 则不能再次打卡，因为 she/he 已经在现场了。 或者，当他们点击钥匙扣时，您保存在日志中，这是一个入口或离开，当您向学生查询 table 时，您按上次插入时间订购 table，这样最后一条记录就会出现在您的位置查看日志的最后状态。
编辑： 在数据库中为学生 table 添加一个额外的 bool 类型列，例如 "studOnsite" 并设置默认值 0。当学生扫描卡片时，您可以从 table 此处获取学生详细信息：
.CommandText = "SELECT * from students where `studtags`='" & studtag.Text & "';"
您还将取回 "studOnsite" 列。在您可以简单地检查值之后：
if (table.Rows(0).Item("studOnsite") then
'student already onsite so she/he is leaving
greet.Text = firstxt.Text & "Good bye!"
'update the student table and change "studOnsite" to false
'dim query as string=string.format("UPDATE students SET studOnsite=false WHERE studtags='{0}'",studtag.Text)
else
'student wasn't onsite so she/he is just arrived
greet.Text = firstxt.Text & "Welcome back!"
'update the student table and change "studOnsite" to true as student is onsite now
'dim query as string=string.format("UPDATE students SET studOnsite=true WHERE studtags='{0}'",studtag.Text)
end if