如何编写这个 LINQ 表达式？

Question

I am creating a web application to manage a flight school and I have the following database structure (unrelevant tables have been blurred and relevant ones have been translated to English for clarity):

I have a table Deadlines that stores all deadlines related to an aircraft. This table is linked to the Aircrafts table. Then I have a OwnedAircrafts table that stores ids of aircrafts and persons (because a person can own several aircrafts or shares of them).

My question is:

Given the id of a person, how can I retrieve the list of deadlines related to his/her aircrafts? (preferrably using method syntax)

In other words:

The following code now returns all the aircraft deadlines, no matter who the owner is. How can I reference the OwnedAircrafts table to filter only the deadlines related to personId ?

    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...
            });

Thank you in advance!

Answer 1

Try following:

    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

Follow this approach:

 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

You can add navigation properties to your entities and then try something like this:

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

You do not need to query the Persons table, as the person Id is available in OwendAircrafts

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...
        });
}

This assumes that you have a navigation property OwnedAircrafts in Aircraft .