Question

我有以下代码：

    Private Sub btnReserve_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnReserve.Click
    Using dbContext As pbu_housingEntities = New pbu_housingEntities
        ' Check that the room is still available.
        Dim hall As String = CStr(Session("hall"))
        Dim room As String = CStr(Session("room"))
        Dim checkOccupants = From p In dbContext.Rooms _
                             Let building_id = p.Building1.id _
                             Where p.building_name = hall _
                             Where p.room1 = room _
                             Select p.current_occupancy, p.max_occupancy, p.id, building_id

        If checkOccupants.First.current_occupancy >= checkOccupants.First.max_occupancy Then
            ' If it isn't available, let the student know.
            lblResult.Text = "Sorry, this room is now fully occupied. Please choose another room."
        Else
            ' Get the current year.
            Dim getYear = From p In dbContext.Configs _
                          Where p.Description = "year" _
                          Select p.textValue
            ' If it is available, add the student to the room.
            Dim Occupant As New Resident
            Dim gender As String = CStr(Session("gender"))
            Dim person_name As String = CStr(Session("person_name"))
            Dim class_level As String = CStr(Session("class_level"))
            Dim semester As String = CStr(Session("term"))
            Dim people_code_id As String = CStr(Session("people_code_id"))
            Dim first_name As String = CStr(Session("first_name"))
            Dim last_name As String = CStr(Session("last_name"))
            Dim building_id As String = checkOccupants.First.building_id
            Dim room_id As String = checkOccupants.First.id
            Occupant.building = building_id
            Occupant.room = room_id
            Occupant.gender = gender
            Occupant.person_name = person_name
            Occupant.class_level = class_level
            Occupant.semester = semester
            Occupant.people_code_id = people_code_id
            Occupant.create_date = Date.Now
            Occupant.first_name = first_name
            Occupant.last_name = last_name
            Occupant.year = getYear.First.ToString
            dbContext.Residents.AddObject(Occupant)

            ' Increment the number of occupants in the room.
            Dim UpdateOccupancy = (From p In dbContext.Rooms _
                   Where p.building_name = hall _
                   Where p.room1 = room _
                   Select p).First
            UpdateOccupancy.current_occupancy = UpdateOccupancy.current_occupancy + 1

            ' Add the student to a bed.
            Dim UpdateBed = From p In dbContext.Beds _
                            Where p.building = building_id _
                            Where p.room = room_id _
                            Where (p.occupant Is Nothing Or p.occupant = 0) _
                            Select p

            ' Get the student's ID from the residency table.
            Dim GetID = (From p In dbContext.Residents _
                        Where p.people_code_id = people_code_id _
                        Order By p.id Descending _
                        Select p.id).FirstOrDefault

            UpdateBed.First.occupant = GetID
            dbContext.SaveChanges()
            lblResult.Text = "Success! You have successfully requested residency in this room!"
            btnBack.Visible = False
            btnReserve.Visible = False
            btnHome.Visible = True
        End If
    End Using
End Sub

问题是，那时

UpdateBed.First.occupant = GetID

执行它总是得0，因为尚未在数据库中创建该行。我可以将最后一段代码移到它自己的Context中，但是有更好的方法吗？

Answer 1

只需在该行前调用SaveChanges即可。

Answer 2

你在UpdateBed.first上缺少一个导航属性，可以让你像这样设置占用者：

UpdateBed.First.Occupant = dbContext.GetPersonById(people_code_id);

有没有办法在不使用两个上下文的情况下使用Entity Framework实现此目的？

2 个答案: