linq-to-sql - Linq to SQL - 如何在插入之前验证记录不存在

Question

我正在为一个客户开发一个小应用程序，他们向我提供了一个城市列表，我必须将它们插入数据库并将它们与他们的父记录相关联。

例子:

ID   |   PID   |   Region
1         0         California
2         1         Los Angeles
3         1         San Fransisco

现在我的代码是这样的

    Dim input As StreamReader
    Dim index As Integer
    Dim filename As String
    Dim RegionDC As New DAL.RegionsDataContext



    For Each TextFile As String In Directory.GetFiles(Server.MapPath("~/app_data/business-trader cities/"))
        input = File.OpenText(TextFile)
        filename = New FileInfo(TextFile).Name
        index = 0


        ''# this is where we want to select the ID for the filename'
        Dim _ID = (From R In RegionDC.bt_Regions _
                 Where R.Region = filename.Replace(".txt", "") _
                 Select R.ID).FirstOrDefault

        While Not input.EndOfStream

            Dim q = (From r In RegionDC.bt_Regions _
                     Where r.Region = input.ReadLine() _
                     Select r.ID).FirstOrDefault

            ''# ***********************************'
            ''#  HERE IS WHERE IM TRYING TO VERIFY'
            ''#  IF THE RECORD EXISTS OR NOT'
            ''# ***********************************'

            ''# now we loop through the txt file'
            ''# and insert the data into the database'
            Dim oRegion As New DAL.bt_Region
            oRegion.Region = input.ReadLine()
            oRegion.FSSearchCount = 0
            oRegion.WSearchCount = 0
            oRegion.PID = _ID

            RegionDC.bt_Regions.InsertOnSubmit(oRegion)
            RegionDC.SubmitChanges()

        End While

        ''# clean up the locked files'
        input.Close()
        input.Dispose()
    Next

所以基本上如果 Los Angeles 在 TXT 文件中，我不希望它重新输入数据库，因为它已经存在。

谁能帮我弄清楚如何在插入之前验证记录是否已经存在？

Answer 1

LINQ To SQL Samples - EXISTS/IN/ANY/ALL

Public Sub LinqToSqlExists01()
    Dim q = From c In db.Customers _
            Where Not c.Orders.Any()

    ObjectDumper.Write(q)
End Sub