LINQ to Entities 不识别方法 - 简单的删除语句

Question

我有一个 GridView，在被删除的行上触发 GridView1_RowDeleting 子项，但收到错误“LINQ to Entities 无法识别方法 'System.Web.UI.WebControls.TableCell get_Item(Int32)' 方法，并且此方法无法翻译成商店表达式。”代码是：

Private Sub GridView1_RowDeleting(sender As Object, e As System.Web.UI.WebControls.GridViewDeleteEventArgs) Handles GridView1.RowDeleting
    ' The deletion of the individual row is automatically handled by the GridView.
    Dim dbDelete As New pbu_housingEntities
    ' Remove individual from the bed.
    Dim remove_bed = From p In dbDelete.Beds _
                     Where p.occupant = GridView1.Rows(e.RowIndex).Cells(3).Text _
                     Where p.room = GridView1.Rows(e.RowIndex).Cells(6).Text _
                     Where p.building = GridView1.Rows(e.RowIndex).Cells(5).Text _
                     Order By p.id Descending _
                     Select p

    remove_bed.First.occupant = ""
    dbDelete.SaveChanges()

    ' Increase number of open spaces in room.
    Dim update_occupancy = From p In dbDelete.Rooms _
                           Where p.room1 = GridView1.Rows(e.RowIndex).Cells(6).Text
                           Where p.building = GridView1.Rows(e.RowIndex).Cells(5).Text _
                           Select p

    update_occupancy.First.current_occupancy = update_occupancy.First.current_occupancy - 1
    dbDelete.SaveChanges()

End Sub

出错的具体行是：

remove_bed.First.occupant = ""

Answer 1

这是因为 Linq 查询已转换为 SQL，并且无法将 GridView1.Rows(e.RowIndex).Cells(3).Text 转换为 SQL。您需要从 GridView 中提取值，然后在查询中使用它们

Dim occupant As String = GridView1.Rows(e.RowIndex).Cells(3).Text
Dim room As String = GridView1.Rows(e.RowIndex).Cells(6).Text
Dim building As String = GridView1.Rows(e.RowIndex).Cells(5).Text
Dim remove_bed = From p In dbDelete.Beds _
                 Where p.occupant = occupant _
                 Where p.room = room _
                 Where p.building = building _
                 Order By p.id Descending _
                 Select p

Answer 2

在执行查询之前，您必须将这些值放入变量中，否则实体提供程序将尝试将整个对象拉入查询中，并在尝试将其转换为 SQL 语句时访问其属性 - 由于没有 SQL，这会失败相等的。