高级搜索 vb.net

Question

我有高级搜索包含 combobox1,combobox2,combobox3 我搜索了一种在数据库中进行搜索的方法。 如果我选择 combobox1 而没有选择 combobox2 和 combobox3 并且如果我选择 combobox2 而不是选择 combobox1 和 combobox3 在 combobox3 和选择所有组合框中我没有找到解决方案，我是否需要为每种情况制作超过 SqlCommand ？或者有一种简单的方法可以做到这一点我尝试制作 SqlCommand

 Public Sub Load_Main(ByVal projectid As Integer, ByVal pdocid As Integer, ByVal depid As Integer)
    main_Datatable.Clear()
    Dim cmd As New SqlCommand("select * from main where projectid=@projectid and pdocid=@pdocid and depid=@depid", DBConnection)

    cmd.Parameters.Add("projectid", SqlDbType.Int).Value = projectid
    cmd.Parameters.Add("pdocid", SqlDbType.Int).Value = pdocid
    cmd.Parameters.Add("depid", SqlDbType.Int).Value = depid
    DBConnection.Open()
    main_Datatable.Load(cmd.ExecuteReader)
    DBConnection.Close()
    cmd = Nothing

End Sub

Load_Main(project_combo.SelectedValue, doc_combo.SelectedValue, Depart_combo.SelectedValue)

但是如果我没有选择另一个组合框，它就不起作用

Answer 1

这是一种方法，无需更改太多代码，假设 0 值表示组合框中没有选择任何内容：

Public Sub Load_Main(ByVal projectid As Integer, ByVal pdocid As Integer, ByVal depid As Integer)
    main_Datatable.Clear()
    Dim query as string
    query = "select * " & _
            "from main " & _
            "where projectid = ISNULL(NULLIF(@projectid, 0), projectid) " & _
            "and pdocid = ISNULL(NULLIF(@pdocid, 0), pdocid) " & _
            "and depid = ISNULL(NULLIF(@depid, 0), depid) "
    Dim cmd As New SqlCommand(query, DBConnection)

    cmd.Parameters.Add("projectid", SqlDbType.Int).Value = projectid
    cmd.Parameters.Add("pdocid", SqlDbType.Int).Value = pdocid
    cmd.Parameters.Add("depid", SqlDbType.Int).Value = depid
    DBConnection.Open()
    main_Datatable.Load(cmd.ExecuteReader)
    DBConnection.Close()
    cmd = Nothing

End Sub

Answer 2

Public Sub Load_Main(ByVal projectid As Integer, ByVal pdocid As Integer, ByVal depid As Integer)
    main_Datatable.Clear()
    Dim cmd As New SqlCommand("select * from main where (@projectid IS NULL OR projectid=@projectid) and (@pdocid IS NULL OR pdocid=@pdocid) and (@depid IS NULL OR depid=@depid)", DBConnection)

    cmd.Parameters.Add("projectid", SqlDbType.Int).Value = If(projectid = 0, CObj(DBNull.Value), projectid)
    cmd.Parameters.Add("pdocid", SqlDbType.Int).Value = If(pdocid = 0, CObj(DBNull.Value), pdocid)
    cmd.Parameters.Add("depid", SqlDbType.Int).Value = If(depid = 0, CObj(DBNull.Value), depid)
    DBConnection.Open()
    main_Datatable.Load(cmd.ExecuteReader)
    DBConnection.Close()
    cmd = Nothing

End Sub

如果您将参数设置为 null，那么它实际上会被忽略，因为它匹配每条记录。由于您的值是作为整数传入的，因此如果您希望在 SQL 子句中忽略它，请将其设置为 0（或其他永远不会使用的整数值，如 -1）。

你应该改用 Using 语句。