访问主键用法/角色 [英] Access Primary Key usage/role

问题描述

我的问题是有关将VB.net项目连接到Access DB的. 我必须在表中有一个主键，还是可以更改我的代码以不寻找PK?

我弹出一个错误，告诉我我没有主键.现在，如果我将"AdminID"设为主键，则系统可以正常工作.我只是在问是否必须这样做?

当前，我的组合框显示"AdminID"，而我宁愿显示"AdminName"

谢谢.

Dim objConnection As New   OleDb.OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source= InfoSystem.accdb")
Dim objAdminDA As New OleDb.OleDbDataAdapter("Select *from tblAdmins", objConnection)
Dim objAdminCB As New OleDb.OleDbCommandBuilder(objAdminDA)
Dim objDataSet As New DataSet()

Public Sub Retrieve()

    'Clears DataSet of any existing data
    objDataSet.Clear()
    'Fills schema - adds table structure information to DataSet
    objAdminDA.FillSchema(objDataSet, SchemaType.Source, "tblAdmins")
    'Fills DataSet with info from the DataAdapter
    objAdminDA.Fill(objDataSet, "tblAdmins")

    'Fill the DataSet with info from the Admin table
    objAdminDA.FillSchema(objDataSet, SchemaType.Source, "tblAdmins")
    objAdminDA.Fill(objDataSet, "tblAdmins")

    'Empty combo box
    cboxAdmin.Items.Clear()

    'Loop through each row, adding the AdminName to the combo box
    Dim i As Integer, strAdminID As String
    For i = 1 To objDataSet.Tables("tblAdmins").Rows.Count
        strAdminID = objDataSet.Tables("tblAdmins").Rows(i - 1).Item("AdminID")
        cboxAdmin.Items.Add(strAdminID)
    Next
    'Select first item in the list
    cboxAdmin.SelectedIndex = 0

    FillAdminDetails()

End Sub

Public Sub FillAdminDetails()
    Dim objRow As DataRow
    objRow = objDataSet.Tables("tblAdmins").Rows.Find(cboxAdmin.SelectedItem.ToString)
    txtStaffDept.Text = objRow.Item("Department")
    txtStaffTitle.Text = objRow.Item("Title")
End Sub

Private Sub cboxAdmin_SelectedIndexChanged(sender As Object, e As EventArgs) Handles cboxAdmin.SelectedIndexChanged
    FillAdminDetails()
End Sub

End Sub

解决方案

您的CBO显示AdminID，因为这就是您要填充的内容.如果将表绑定到CBO，则可以使用DisplayMember显示一件事，并使用ValueMember将另一件事返回到您的代码:

Private ACEConnStr = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source= InfoSystem.accdb"
Private dtAdmin As DataTable
...
Private Sub SetupCBO
    Dim SQL = "SELECT AdminId, AdminName FROM tblAdmin"

    Using dbcon As New OleDbConnection(ACEConnStr)
        Using cmd As New OleDbCommand(SQL, dbcon)

            dbcon.Open()
            dtAdmin = New DataTable

            dtAdmin.Load(cmd.ExecuteReader())
        End Using
    End Using

    cboAdmin.DataSource = dtAdmin
    cboAdmin.DisplayMember = "AdminName"     ' what to show
    cboAdmin.ValueMember = "AdminId"         ' what field to report
End Sub

首先要注意的是，没有代码可以直接填充CBO.使用DataSource，cbo将从基础表中获取数据. DisplayMember告诉它...可以显示，显示哪一列，并且ValueMember允许您的代码能够获取该PrimaryKey/Id来肯定地知道哪个"Steve"或"Bob"正在登录. >

还请注意，您不必绝对只需要DataAdapter即可填写一张桌子.您也不需要 DataSet.如图所示，可以将Load方法与DataReader一起使用以直接填充表格. Using块关闭并处置那些释放资源的对象.

绑定后，通常会使用SelectedValueChanged事件并使用.SelectedValue.

在这种情况下，SelectedItem将是一个DataRowView对象，因为NET创建了一个DataView包装器.如果数据源是List(Of Employee)或List(of Widget)，则SelectedItem将成为所选的Employee或Widget.

My question is in relation to connecting a VB.net project to an Access DB. Must I have a primary key in my table, or have is there a way to alter my code to not look for a PK?

I have an error popping up telling me that I have no primary key. Now if i make "AdminID" my primary key, the system works. I was just questioning as to whether or not this is required?

Currently my combobox displays "AdminID" where as I would rather it display "AdminName"

Thanks.

Dim objConnection As New   OleDb.OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source= InfoSystem.accdb")
Dim objAdminDA As New OleDb.OleDbDataAdapter("Select *from tblAdmins", objConnection)
Dim objAdminCB As New OleDb.OleDbCommandBuilder(objAdminDA)
Dim objDataSet As New DataSet()

Public Sub Retrieve()

    'Clears DataSet of any existing data
    objDataSet.Clear()
    'Fills schema - adds table structure information to DataSet
    objAdminDA.FillSchema(objDataSet, SchemaType.Source, "tblAdmins")
    'Fills DataSet with info from the DataAdapter
    objAdminDA.Fill(objDataSet, "tblAdmins")

    'Fill the DataSet with info from the Admin table
    objAdminDA.FillSchema(objDataSet, SchemaType.Source, "tblAdmins")
    objAdminDA.Fill(objDataSet, "tblAdmins")

    'Empty combo box
    cboxAdmin.Items.Clear()

    'Loop through each row, adding the AdminName to the combo box
    Dim i As Integer, strAdminID As String
    For i = 1 To objDataSet.Tables("tblAdmins").Rows.Count
        strAdminID = objDataSet.Tables("tblAdmins").Rows(i - 1).Item("AdminID")
        cboxAdmin.Items.Add(strAdminID)
    Next
    'Select first item in the list
    cboxAdmin.SelectedIndex = 0

    FillAdminDetails()

End Sub

Public Sub FillAdminDetails()
    Dim objRow As DataRow
    objRow = objDataSet.Tables("tblAdmins").Rows.Find(cboxAdmin.SelectedItem.ToString)
    txtStaffDept.Text = objRow.Item("Department")
    txtStaffTitle.Text = objRow.Item("Title")
End Sub

Private Sub cboxAdmin_SelectedIndexChanged(sender As Object, e As EventArgs) Handles cboxAdmin.SelectedIndexChanged
    FillAdminDetails()
End Sub

End Sub

解决方案

Your CBO shows AdminID because that is what you fill it with. If you bind the table to the CBO, you can use DisplayMember to show one thing, and ValueMember to return another to your code:

Private ACEConnStr = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source= InfoSystem.accdb"
Private dtAdmin As DataTable
...
Private Sub SetupCBO
    Dim SQL = "SELECT AdminId, AdminName FROM tblAdmin"

    Using dbcon As New OleDbConnection(ACEConnStr)
        Using cmd As New OleDbCommand(SQL, dbcon)

            dbcon.Open()
            dtAdmin = New DataTable

            dtAdmin.Load(cmd.ExecuteReader())
        End Using
    End Using

    cboAdmin.DataSource = dtAdmin
    cboAdmin.DisplayMember = "AdminName"     ' what to show
    cboAdmin.ValueMember = "AdminId"         ' what field to report
End Sub

The first thing to note is that there is no code to populate the CBO directly. Using a DataSource, the cbo will get the data from the underlying table. The DisplayMember tells it which column to...well, display, and the ValueMember allows your code to be able to fetch that PrimaryKey/Id to positively know which "Steve" or "Bob" is logging in.

Also note that you don't absolutely need a DataAdapter just to fill one table. Nor do you need DataSet. As shown, you can use the Load method with a DataReader to directly fill a table. The Using blocks close and dispose of those objects freeing resources.

When bound, you would generally use the SelectedValueChanged event and use the .SelectedValue.

In this case, the SelectedItem will be a DataRowView object because NET creates a DataView wrapper. If the data source was a List(Of Employee) or a List(of Widget), the SelectedItem will be the selected Employee or Widget.

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