如何过滤“包含"?实体框架中的实体?

How to filter quot;Includequot; entities in entity framework?(如何过滤“包含?实体框架中的实体?)

问题描述

实体:

    public class Room
    {
        public Room()
        {
            this.Reservations = new HashSet<Reservation>();
        }

        public int Id { get; set; }

        public decimal Rate { get; set; }

        public int HotelId { get; set; }

        public virtual Hotel Hotel { get; set; }

        public virtual ICollection<Reservation> Reservations { get; set; }
    }

    public class Hotel
    {
        public Hotel()
        {
            this.Rooms = new HashSet<Room>();
        }

        public int Id { get; set; }

        public string Name { get; set; }

        public virtual ICollection<Room> Rooms { get; set; }
    }

    public class Reservation
    {
        public int Id { get; set; }

        public DateTime StartDate { get; set; }

        public DateTime EndDate { get; set; }

        public string ContactName { get; set; }

        public int RoomId { get; set; }

        public virtual Room Room { get; set; }
    }

  public class ExecutiveSuite : Room
  {
  }

  public class DataContext : DbContext
    {
        public DbSet<Hotel> Hotels { get; set; }

        public DbSet<Reservation> Reservations { get; set; }

        public DbSet<Room> Rooms { get; set; }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Room>()
                .HasKey(r => r.Id)
                .HasRequired(r => r.Hotel)
                .WithMany(r => r.Rooms)
                .HasForeignKey(r => r.HotelId);

            modelBuilder.Entity<Hotel>()
                .HasKey(h => h.Id);

            modelBuilder.Entity<Room>()
                .HasMany(r => r.Reservations)
                .WithRequired(r => r.Room)
                .HasForeignKey(r => r.RoomId);

        }
    }

客户端代码(控制台应用):

The client code(console app):

static void Main(string[] args)
        {
            // initialize and seed the database
            using (var context = new DataContext())
            {
                var hotel = new Hotel { Name = "Grand Seasons Hotel" };
                var r101 = new Room { Rate = 79.95M, Hotel = hotel };
                var es201 = new ExecutiveSuite { Rate = 179.95M, Hotel = hotel };
                var es301 = new ExecutiveSuite { Rate = 299.95M, Hotel = hotel };

                var res1 = new Reservation
                {
                    StartDate = DateTime.Parse("3/12/2010"),
                    EndDate = DateTime.Parse("3/14/2010"),
                    ContactName = "Roberta Jones",
                    Room = es301
                };
                var res2 = new Reservation
                {
                    StartDate = DateTime.Parse("1/18/2010"),
                    EndDate = DateTime.Parse("1/28/2010"),
                    ContactName = "Bill Meyers",
                    Room = es301
                };
                var res3 = new Reservation
                {
                    StartDate = DateTime.Parse("2/5/2010"),
                    EndDate = DateTime.Parse("2/6/2010"),
                    ContactName = "Robin Rosen",
                    Room = r101
                };

                es301.Reservations.Add(res1);
                es301.Reservations.Add(res2);
                r101.Reservations.Add(res3);

                hotel.Rooms.Add(r101);
                hotel.Rooms.Add(es201);
                hotel.Rooms.Add(es301);

                context.Hotels.Add(hotel);
                context.SaveChanges();
            }

            using (var context = new DataContext())
            {
                context.Configuration.LazyLoadingEnabled = false;
                // Assume we have an instance of hotel
                var hotel = context.Hotels.First();

                // Explicit loading with Load() provides opportunity to filter related data 
                // obtained from the Include() method 
                context.Entry(hotel)
                       .Collection(x => x.Rooms)
                       .Query()
                       .Include(y => y.Reservations)
                       .Where(y => y is ExecutiveSuite && y.Reservations.Any())
                       .Load();

                Console.WriteLine("Executive Suites for {0} with reservations", hotel.Name);

                foreach (var room in hotel.Rooms)
                {
                    Console.WriteLine("
Executive Suite {0} is {1} per night", room.Id,
                                      room.Rate.ToString("C"));
                    Console.WriteLine("Current reservations are:");
                    foreach (var res in room.Reservations.OrderBy(r => r.StartDate))
                    {
                        Console.WriteLine("	{0} thru {1} ({2})", res.StartDate.ToShortDateString(),
                                          res.EndDate.ToShortDateString(), res.ContactName);
                    }
                }
            }

            Console.WriteLine("Press <enter> to continue...");
            Console.ReadLine();
        }



using ( var context = new DataContext() )
{

        //context.Configuration.LazyLoadingEnabled = false;

        // Assume we have an instance of hotel
        var hotel = context.Hotels.First();
        var rooms = context.Rooms.Include( r => r.Reservations ).Where( r => r is ExecutiveSuite && r.Reservations.Any() ).Where( r => r.Hotel.Id == hotel.Id );
        Console.WriteLine( "Executive Suites for {0} with reservations", hotel.Name );

        foreach ( var room in hotel.Rooms )
        {
           Console.WriteLine( "
Executive Suite {0} is {1} per night", room.Id,
                             room.Rate.ToString( "C" ) );
           Console.WriteLine( "Current reservations are:" );
           foreach ( var res in room.Reservations.OrderBy( r => r.StartDate ) )
           {
              Console.WriteLine( "	{0} thru {1} ({2})", res.StartDate.ToShortDateString(),
                                res.EndDate.ToShortDateString(), res.ContactName );
           }
        }
     }

我尝试将其投影并放入匿名对象中:

I tried projecting and putting it in an anonymous object:

       var hotel = context.Hotels.Select(h =>
        new 
        {   
            Id = h.Id,
            Name = h.Name,
            Rooms = h.Rooms.Where(r => r.Reservations is ExecutiveSuite && r.Reservations.Any())
        }).First();

但我得到一个例外:DbIsOfExpression 需要一个表达式参数，该表达式参数具有与类型参数兼容的多态结果类型."

but I get an exception: "DbIsOfExpression requires an expression argument with a polymorphic result type that is compatible with the type argument."

现在，如果您注意到，我以两种不同的方式实现它，首先是通过显式加载相关实体，其次是通过两个不同的查询，我的问题是，有没有一种方法可以加载我的对象图并过滤我包含"的实体，只需一次从数据库中访问?

Now, if you would notice, I implemented it in two different ways, first was by explicitly loading the related entities, second was by having two different queries, my question would be, is there a way I can load my object graph and filter the entities I "Include" with just a single trip from the database?

推荐答案

过滤包含实体有两种方式.

There are two ways to filter include Entity.

• 使用投影(参见@Eldho 答案)
• 使用第三方库

免责声明:我是项目的所有者Entity Framework Plus

EF+ Query IncludeFilter 允许轻松过滤包含的实体.

The EF+ Query IncludeFilter allows to easily filter included entities.

context.Entry(hotel)
       .Collection(x => x.Rooms)
       .Query()
       .IncludeFilter(y => y.Reservations
                            .Where(z => z is ExecutiveSuite && z.Reservations.Any())
       .Load();

在引擎盖下，图书馆确实做了一个投影.

Under the hood, the library does exactly a projection.

Wiki:EF+ 查询包含过滤器

编辑:回答子问题

你几乎做到了.房间已包含并过滤，但您未包含预订.

You almost did it. The rooms were included and filtered, but you didn't include the reservations.

var hotel = context.Hotels
    // Include only executive suite with a reservation
    .IncludeFilter(x => x.Rooms.Where(y => y is ExecutiveSuite && y.Reservations.Any()))
    // Include only reservation from executive suite
    .IncludeFilter(x => x.Rooms.Where(y => y is ExecutiveSuite).Select(z => z.Reservations))
    .First();

---

回答评论

我们如何使用包含过滤器包含多级属性

How can we include multilevel properties with include filter

您可以通过指定每个路径(每个 IncludeFilter 一个)来包含多级

You can include multilevel by specifying each path (one per IncludeFilter)

所以 qry.Include("Rooms.Hotel") 变成:

qry.IncludeFilter(x => x.Rooms)
   .IncludeFilter(x => x.Rooms.Select(y => y.Hotel))

---

回答评论

EF+ 是否支持 dotnet 5.0?

does EF+ have dotnet 5.0 support?

是的，它支持 dotnet 5.0 和 EF Core 5.0.但是，对于 IncludeFilter，您还应该直接在 EF Core 5 中查看已过滤的 include:https://www.learnentityframeworkcore5.com/whats-new-in-ef-core-5/filtered-included

Yes, it supports dotnet 5.0 and EF Core 5.0. However, for IncludeFilter, you should also look at the filtered include built-in directly in EF Core 5: https://www.learnentityframeworkcore5.com/whats-new-in-ef-core-5/filtered-included

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