Question

我需要创建一个LINQ语句，该语句使用用户从组合框中选择的国家/地区，并在列表框中显示数据库中的城市。附件就是我到目前为止所拥有的。有许多国家因此使用if语句将不起作用。

Private Sub ComboBox1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ComboBox1.SelectedIndexChanged
    Dim myQ1 = From X In CustomersDataset.Customers Where

    X.Country = ComboBox1.SelectedItem Select X.City 

    '(X.Country = "France" Select X.City)-only shows city options for France obviously.


    lstCity.DataSource = myQ1.ToList
End Sub

Answer 1

ComboBox SelectedItem属于Object类型，是它的界限。因此，您必须将DataRowView强制转换为String，以便可以在linq查询中进行比较：

Dim strSelectedItemValue As String = CType(ComboBox1.SelectedItem, DataRowView).Item("ReplaceWithTheColumnNameOfTheCountryField")

Dim myQ1 = From X In CustomersDataset.Customers 
Where X.Country = strSelectedItemValue
Select X.City

lstCity.DataSource = myQ1.ToList
lstCity.DataBind()

Combox和LINQ - Visual Basic

1 个答案: