在我的程序中,用户可以将学生组合到一个班级中。在我的代码中,似乎有一些奇怪的逻辑错误;我的数据库通过StudentsGroups
表将一个组链接到学生。虽然输入应该是这样的:添加到数据库时出现逻辑错误
+---------------------+----------------------------------+
| studentsgroups | groups |
+---------+-----------+---------+-----------+------------+
| groupID | studentID | groupID | groupName | groupFocus |
+---------+-----------+---------+-----------+------------+
| 1 | 1 | 1 | TestGroup | Maths |
| 1 | 2 +---------+-----------+------------+
| 1 | 3 |
+---------+-----------+
我的输出,而不是像这样:
+---------+-----------+
| groupID | studentID |
+---------+-----------+
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
+---------+-----------+
随着groups
表是空的。我没有收到任何错误消息,所以据我所知,我的代码运行良好,但在某个地方出现问题。
Private Sub btnSubmit_Click(sender As Object, e As EventArgs) Handles btnSubmit.Click
' We create a new instance of a Groups object to store our entered values; the group's name
' the group's focus and the students in this group
Dim newGroup As New Groups
newGroup.strGroupName = txtGroupName.Text
newGroup.strGroupFocus = cmbGroupFocus.SelectedValue
' We add every student in this group list to the Groups object's student list.
For i As Integer = 0 To lstGroupList.Items.Count - 1
newGroup.addStudent(groupList.Item(i))
Next
' Firstly, we must insert a new group into the database. This will allow us to link every
' student in the group to this group in our StudentsGroups table.
Using conn As New MySqlConnection(connString)
conn.Open()
Using cmd As New MySqlCommand
cmd.Connection = conn
cmd.CommandText = "INSERT INTO groups(groupName, groupFocus) VALUES(@grpName, @grpFocus);"
cmd.Parameters.AddWithValue("@grpName", newGroup.strGroupName)
cmd.Parameters.AddWithValue("@grpFocus", newGroup.strGroupFocus)
End Using
conn.Close()
End Using
Try
' To get the ID of the group generated by the database, we make a temporary string to
' hold the ID value.
Dim groupID As String
Using conn As New MySqlConnection(connString)
conn.Open()
Using selComm As New MySqlCommand
' We create a SELECT query to find the new ID by using the entered group's name.
selComm.Connection = conn
selComm.CommandText = "SELECT groupID FROM groups WHERE groupName = @groupName;"
selComm.Parameters.AddWithValue("@groupName", newGroup.strGroupName)
selComm.Prepare()
' We use the ExecuteScalar method, which would return the very first entry on the
' first row. Since we only want one row and one result, this is better than using
' a DataTable and DataReader.
groupID = selComm.ExecuteScalar()
End Using
conn.Close()
End Using
' Now we begin to link the students to their group. We run through every student in the
' group list and add in their ID along with the group's ID to the table.
For i As Integer = 0 To groupList.Count - 1
Using conn As New MySqlConnection(connString)
conn.Open()
Using newCommand As New MySqlCommand
newCommand.Connection = conn
newCommand.CommandText = "INSERT INTO studentsgroups VALUES(@groupID, @studentID);"
newCommand.Parameters.AddWithValue("@groupID", CInt(groupID))
' To get the student's ID, we do the same process as above; make a new
' command to get the student's ID, using ExecuteScalar.
Dim studentID As String
' When processing a new command, we need a new connection item to
Using conn2 As New MySqlConnection(connString)
conn2.Open()
Using comm2 As New MySqlCommand
comm2.Connection = conn2
comm2.CommandText = "SELECT idNumber FROM students WHERE passCode = @passcode"
comm2.Parameters.AddWithValue("@passcode", groupList.Item(i).intIDNum)
comm2.Prepare()
studentID = comm2.ExecuteScalar()
End Using
conn2.Close()
End Using
newCommand.Parameters.AddWithValue("@studentID", CInt(studentID))
newCommand.Prepare()
newCommand.ExecuteNonQuery()
End Using
conn.Close()
End Using
Next
Catch ex As Exception
MsgBox("Error: " & ex.ToString())
Finally
MsgBox("New Group created!")
Me.Close()
End Try
End Sub
这里是提交部分的相关代码,有人会知道逻辑问题可能出现在哪里吗?
最初的困惑更多的是我自己,因为我在数据库之前制定了很多加入学生的代码。所以当程序引用'IDNum'时,这与'passCode'列相同。但是,是的,这就是我想从我的代码中,将组中的每个人添加到列表中。 –