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(控制台应用程序):
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("\nExecutive 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("\t{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( "\nExecutive 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( "\t{0} thru {1} ({2})", res.StartDate.ToShortDateString(),
res.EndDate.ToShortDateString(), res.ContactName );
}
}
}
我尝试投影并将其放入匿名对象中:
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();
但我得到一个异常:“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。”
现在，如果你注意到了，我用两种不同的方式实现它，第一种是显式加载相关实体，第二种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通过数据库中的一次行程过滤我“包含”的实体？
最佳答案
有两种过滤包含实体的方法。
- 使用投影(参见@Eldho 的回答)
- 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。
context.Entry(hotel)
.Collection(x => x.Rooms)
.Query()
.IncludeFilter(y => y.Reservations
.Where(z => z is ExecutiveSuite && z.Reservations.Any())
.Load();
在幕后，图书馆做了一个精确的投影。
编辑:回答子问题
你几乎做到了。房间已包括在内并经过筛选，但您没有包括预订。
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();
编辑:回答评论
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
所以 qry.Include("Rooms.Hotel") 变成:
qry.IncludeFilter(x => x.Rooms)
.IncludeFilter(x => x.Rooms.Select(y => y.Hotel))
编辑:回答评论
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，您还应该查看直接在 EF Core 5 中内置的已过滤 include:https://www.learnentityframeworkcore5.com/whats-new-in-ef-core-5/filtered-included
关于c# - 如何在 Entity Framework 中过滤 "Include"实体？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/39636952/