有没有一种方法可以在不使用两个上下文的情况下使用实体框架来完成此任务？

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，

UpdateBed.First.occupant = GetID

执行时它总是得到 0，因为该行尚未在数据库中创建。我可以将最后一段代码移到它自己的上下文中，但是有更好的方法吗？

Answer 1

只需在该行之前调用 SaveChanges 即可。

Answer 2

您在 UpdateBed.first 上缺少占用者的导航属性，该属性允许您像这样设置占用者：

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