如何编写此 LINQ 表达式？

Question

我正在创建一个 web 应用程序来管理飞行学校，我有以下数据库结构（不相关的 table 已被模糊处理，相关的已被翻译成英文以便清楚）：

我有一个 table Deadlines 存储与飞机相关的所有截止日期。此 table 链接到 Aircrafts table。然后我有一个 OwnedAircrafts table 存储飞机和人员的 ID（因为一个人可以拥有多架飞机或其中的一部分）。

我的问题是：

给定一个人的 ID，如何检索与 his/her 飞机相关的截止日期列表？（最好使用方法语法）

换句话说：

下面的代码现在returns所有飞机的截止日期，不管主人是谁。我如何引用 OwnedAircrafts table 以仅过滤与 personId?

相关的截止日期

    IEnumerable<DeadlineViewModel> GetDeadlinesOfAPerson(long personId)
    {
        return _context.Deadlines
            .Select(deadline => new DeadlineViewModel
            {
                Id = deadline.Id,
                Aircraft = deadline.Aircraft,
                Model = deadline.AircraftsNavigation.Model,
                IdDeadlineType = deadline.DeadlineType,
                DeadlineType = deadline.DeadlineTypesNavigation.Description
                // other fields...
            });

提前致谢！

Answer 1

尝试以下操作：

    IEnumerable<DeadlineViewModel> GetDeadlinesOfAPerson(long personId)
    {
        return _context.Deadlines
            .Where(x => x.deadline.ID == 12345)
            .Select(deadline => new DeadlineViewModel
            {
                Id = deadline.Id,
                Aircraft = deadline.Aircraft,
                Model = deadline.AircraftsNavigation.Model,
                IdDeadlineType = deadline.DeadlineType,
                DeadlineType = deadline.DeadlineTypesNavigation.Description
                // other fields...
            });

Answer 2

遵循这种方法：

 IEnumerable<DeadlineViewModel> GetDeadlinesOfAPerson(long personId)
{
    return _context
        .OwnedAircarfs
        .Where( s => s.Persona == YourPersonId)
        .Includes(s=> s.AirCrafts)
          .ThenIncludes(s=> s.Deadlines)
       
        .Select(deadline => new DeadlineViewModel
        {
             //use navigation properties to get value of related tables
            // other fields...
        }).ToList();

Answer 3

您可以向您的实体添加导航属性，然后尝试这样的操作：

var user = _context.Users
    .Include(user => user.OwnedAircrafts)
        .ThenInclude(ownedAircraft => ownedAircraft.Aircraft)
            .ThenInclude(aircraft => aircraft.Deadlines)
    .FirstOrDefault(user => user.Id == userId)

return user.OwnedAircrafts
    .SelectMany(ownedAircraft => ownedAircraft.Aircraft.Deadlines);

Answer 4

您不需要查询人员 table，因为人员 ID 在 OwendAircrafts

中可用

IEnumerable<DeadlineViewModel> GetDeadlinesOfAPerson(long personId)
{
    return _context.Deadlines
        .Where(deadline =>
            deadline.Aircraft.OwnedAircrafts.Any(oa => oa.persona == personId))
        .Select(deadline => new DeadlineViewModel
        {
            Id = deadline.Id,
            Aircraft = deadline.Aircraft,
            Model = deadline.AircraftsNavigation.Model,
            IdDeadlineType = deadline.DeadlineType,
            DeadlineType = deadline.DeadlineTypesNavigation.Description
            // other fields...
        });
}

这假设您在 Aircraft 中有一个导航属性 OwnedAircrafts。

如何编写此 LINQ 表达式？

How can I compose this LINQ expression?

c#

linq

database