需要 LINQ 表达式根据外键值过滤表
我有一张世界事件表。每个世界事件都有一个在某个国家/地区发生的与该世界事件相关的演示列表
public class WorldEvent
{
public int ID { get; set; }
public string Name { get; set; }
public List<Presentation> PresentationList { get; set; }
}
public class Presentation
{
public int ID { get; set; }
public string Name { get; set; }
public string Country { get; set; }
}
public class WorldEventService
{
public List<WorldEvent> GetWorldEvents()
{
List<WorldEvent> worldEventList = new List<WorldEvent>();
List<Presentation> presentationList = new List<Presentation>();
// Create list of Presentations for WorldEvent_1
presentationList = new List<Presentation>()
{
new Presentation() { ID = 1, Name = "Presentation_1", Country = "Germany",},
new Presentation() { ID = 2, Name = "Presentation_2", Country = "UK",},
new Presentation() { ID = 3, Name = "Presentation_3", Country = "UK",},
};
// Add WorldEvent_1 to the list of WorldEvents
worldEventList.Add(new WorldEvent()
{
ID = 1,
Name = "WorldEvent_1",
PresentationList = presentationList,
});
// Create list of Presentations for WorldEvent_2
presentationList = new List<Presentation>()
{
new Presentation() { ID = 4, Name = "Presentation_4", Country = "USA",},
new Presentation() { ID = 5, Name = "Presentation_5", Country = "UK",},
new Presentation() { ID = 6, Name = "Presentation_6", Country = "Japan",},
};
现在 - 我怎样才能获得在英国进行演示的 WorldEvents 列表。而且 - 在我感兴趣的列表中，WorldEvents 应仅包含有关英国演示文稿的信息。换句话说，我需要这个结果：
世界事件_1（演示文稿_2、演示文稿_3）
世界事件_2（演示_5）
德玛西亚994回答
-
慕村9548890
如果我明白你想要什么。有很多方法可以做到这一点，但是您可以先进行过滤，然后WorldEvents使用过滤后的列表重新创建Presentationvar country = "UK";var result = worldEventList.Where(x => x.PresentationList.Any(y => y.Country == country)) .Select(x => new WorldEvent() { ID = x.ID, Name = x.Name, PresentationList = x.PresentationList .Where(y => y.Country == country) .ToList() }).ToList();或者正如Gert Arnold在评论中指出的那样，您可以在事后过滤var result = worldEventList.Select(x => new WorldEvent() { ID = x.ID, Name = x.Name, PresentationList = x.PresentationList .Where(y => y.Country == country).ToList() }).Where(x => x.PresentationList.Any()) .ToList();注意：因为这不是投影（选择）每个Presentation，所以您对 aPresentation中所做的任何更改都result将反映在原始数据中。如果您不希望这样，则需要重新创建每个Presentation -
吃鸡游戏
var worldEvent = new WorldEventService.GetWorldEvents();var filter = "";//userInputvar filteredResult = worldEvent.Select(r => new WorldEvent { PresentationList = r.PresentationList.Where(c => c.Country == filter).ToList(), ID = r.Id, Name = r.Name }).ToList(); -
慕容森
public static List<WorldEvent> Filter(string Country, List<WorldEvent> events) { var evs = from ev in events.Where(x => x.PresentationList.Any(y => y.Country == Country)) let targetPres = from pres in ev.PresentationList where pres.Country == Country select pres select new WorldEvent { ID = ev.ID, Name = ev.Name, PresentationList = targetPres.ToList() }; return evs.ToList(); } -
繁星coding
不确定我的理解是否正确，我猜您的 WorldEvent 和演示表之间存在一对多的关系。因此，如果您想通过使用 EntityFramework 获取在英国发生的所有 WorldEvents 及其相关演示，您可以尝试以下操作：worldEventContext .Include(PresentationContext) .Select( w => new { w.ID, w.Name, PresentationList = w.PresentationContext.Where(p => p.Country == "UK") })
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C#