[英]LINQ select items in a list that are all in a list of another type
我有使用實體框架創建的多對多關系。
public class Animal
{
[Key]
[DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
public int AnimalID { get; set; }
[MaxLength(50)]
public string AnimalName { get; set; }
public virtual ICollection<Food> FoodList { get; set; }
}
public class Den
{
[Key]
[DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
public int DenID { get; set; }
[MaxLength(50)]
public string DenName { get; set; }
public virtual ICollection<Food> FoodList { get; set; }
}
Animal和Den都包含類型食物的虛擬列表。
public class Food
{
[Key]
[DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
public int FoodID { get; set; }
[MaxLength(50)]
public string FoodName { get; set; }
public virtual ICollection<Animal> AnimalList { get; set; }
public virtual ICollection<Den> DenList { get; set; }
}
我有一個傳遞DenID的方法,我需要返回一個動物列表,其中所有動物的Animal.FoodList中都包含Den的Den.FoodList。
例如,如果Den.FoodList包含Meat和Veg,則我想要一個在foodList中包含Meat和Veg的動物的列表。
編輯
到目前為止,我已經嘗試了一些方法。
首先,我在ViewModel中有這個
denFoodList = new List<Food>();
//Check if myDen requires any Food.
denFoodList = MyDen.FoodList.ToList();
我嘗試遍歷DenFoodList的每個成員,並將Animals添加到Animal列表中,然后收集列表中的任何動物x次(其中x是FoodList.Count())是我需要的動物,但是此方法是緩慢而混亂。
我嘗試將All方法與動物列表和DenList一起使用,但無法正常工作。
animalList = context.Animals.Where(a => a.FoodList.All(f => f.DenList));
我一直在研究使用連接和相交,但在使用它們來解決此問題方面還沒有成功。
編輯結束
任何幫助表示贊賞。 謝謝。
未經測試:
class Test
{
private static IEnumerable<Den> Dens()
{
var dens = new List<Den>
{
new Den
{
DenID = 1,
DenName = "GamePark",
FoodList = new Collection<Food>()
{
new Food
{
FoodID = 1,
FoodName = "Veg",
AnimalList = new Collection<Animal>
{
new Animal
{
AnimalID = 234,
AnimalName = "Zebra",
FoodList = new Collection<Food>{new Food {FoodID = 1, FoodName = "Veg"} }
},
new Animal
{
AnimalID = 125,
AnimalName = "Buffalo",
FoodList = new Collection<Food>{new Food {FoodID = 1, FoodName = "Veg"} }
}
}
},
new Food
{
FoodID = 2,
FoodName = "Meat",
AnimalList = new Collection<Animal>
{
new Animal
{
AnimalID = 003,
AnimalName = "Leopard",
FoodList = new Collection<Food>{new Food {FoodID = 2, FoodName = "Meat"} }
},
new Animal
{
AnimalID = 001,
AnimalName = "Lion",
FoodList = new Collection<Food>{new Food {FoodID = 2, FoodName = "Meat"} }
}
}
}
}
}
};
return dens;
}
public static IEnumerable<Animal> GetAnimalsWithFoodsInDen(int denId)
{
var den = Dens().FirstOrDefault(x => x.DenID == denId);
var animals = new List<Animal>();
if (den != null)
{
var foods = den.FoodList;
if (foods != null)
{
animals = foods.ToList().Aggregate(animals, (current, food) => current.Union(food.AnimalList).ToList());
}
}
return animals;
}
static void Main(string[] args)
{
var result = GetAnimalsWithFoodsInDen(1);
foreach (var a in result)
{
Console.WriteLine(a.AnimalName);
}
Console.ReadLine();
}
}
讓我們嘗試一下
class MyContext : DbContext {}
// ...
using (MyContext context = new MyContext())
{
var den = context.Den.Find(DenId);
// Inner join Linq
var foodList = from a in context.Animals
from b in a.FoodList
join c in d.FoodList on c.FoodId equals b.FoodId
select c;
}
首先獲取食物清單,然后獲取動物:
Den d = SomeDen();
var food = d.FoodList;
var animals = new List<Animal>();
foreach(var f in food) foreach(var a in f.AnimalList) if(!animals.Contains(a)) animals.Add(a);
也許您希望使用字典而不是List來提高性能,具體取決於您的數據。
還是您正在尋找類似的東西?
Dan d = SomeDen();
var food = d.FoodList;
var animals = from a in DB.Animals
where a.FoodList.Any((f)=>food.Contains(f))
select a;
后者應該是您的直覺主意,但是會很慢。
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