如何使用linq从数据库中删除记录？

我正在尝试使用LINQ从数据库中删除一条记录。我给了系统要删除的行键，它确实返回了一行

这是我的密码：

 Public Function DeleteHydrantByKey(ByVal objDeptGUID As String, ByVal objLogonToken As String, ByVal objSesionToken As String, ByVal objHydrantKey As Integer) As String
    'Check if Token is good
    If CheckToken(objSesionToken, objDeptGUID) = False Then
        Return "Session Error"
    End If
    'Check if login Token is good
    If CheckLoginToken(objDeptGUID, objLogonToken) = False Then
        Return "Logon Session Error"
    End If

    Try
        Dim lbHydrants As New linqAlarmDumpDataContext

        'Check for Hydrans in system
        Dim GetHydrants = From r In lbHydrants.tbHydrants _
                          Where r.key = objHydrantKey
                          Select r

        'Check For Hydrent Data
        If GetHydrants.Count = 0 Then
            Return "Not Found"
        End If


        'Deletes Hydrent Data After Check was ok
        lbHydrants.tbHydrants.DeleteOnSubmit(GetHydrants)
        lbHydrants.SubmitChanges()



        Return "OK"
    Catch ex As Exception
        Return "Error"
    End Try
End Function

    Public Function DeleteHydrantByKey(ByVal objDeptGUID As String, ByVal objLogonToken As String, ByVal objSesionToken As String, ByVal objHydrantKey As Integer) As String
    'Check if Token is good
    If CheckToken(objSesionToken, objDeptGUID) = False Then
        Return "Session Error"
    End If
    'Check if login Token is good
    If CheckLoginToken(objDeptGUID, objLogonToken) = False Then
        Return "Logon Session Error"
    End If

    Try
        Dim lqHydrants As New linqAlarmDumpDataContext

        'Check for Hydrans in system
        Dim GetHydrants = From r In lqHydrants.tbHydrants _
                          Where r.key = objHydrantKey
                          Select r

        'Check For Hydrent Data
        If GetHydrants.Count = 0 Then
            Return "Not Found"
        End If


        'Deletes Hydrent Data After Check was ok
        lqHydrants.tbHydrants.DeleteAllOnSubmit(GetHydrants)
        lqHydrants.SubmitChanges()



        Return "OK"
    Catch ex As Exception
        Return "Error"
    End Try
End Function