class PetOwner

{

public string Name { get; set; }

public List
     
       Pet { get; set; }
     

}

class Pet

{

public int Id { get; set; }

public string Name { get; set; }

public int Age { get; set; }

}

class Program

{

static void Main(string[] args)

{

PetOwner[] petOwners =

{ new PetOwner { Name="zzl",

Pet = new List
     
      {
   new Pet{Id=1,Name="小狗"},new Pet{Id=2,Name="小猫"},new Pet{Id=3,Name="小老虎"} } },
     

new PetOwner { Name="zql",

Pet = new List
     
      {
   new Pet{Id=1,Name="小狗"} } },
     

new PetOwner { Name="zhz",

Pet = new List
     
      {
   new Pet{Id=1,Name="小狗"},new Pet{Id=3,Name="小老虎"} } },
     

};

List
     
       PetList = new List
      
     

{

new Pet { Id = 1, Name = "小狗",Age=1 },

new Pet { Id = 2, Name = "小猫",Age=2 },

new Pet { Id = 3, Name = "小老虎",Age=1},

new Pet { Id = 4, Name = "小蛇",Age=3 },

new Pet { Id = 5, Name = "小蝎子",Age=2 },

new Pet { Id = 6, Name = "小兔子",Age=3},

};

#region 不知道SelectMany之前，选择LIST是多么的悲哀

List
     
       query2 = new List
      
       ();
      
     

petOwners.AsQueryable().Where(i => i.Name == "zzl").ToList().ForEach(i =>

{

query2.AddRange(i.Pet);

});

foreach (Pet pet in query2)

Console.WriteLine(pet.Name);

#endregion

#region 有了SelectMany，我们的代码的可读及执行效率上都有所提高

List<Pet> query1 = petOwners.AsQueryable().Where(i => i.Name == "zzl")

.SelectMany(i => i.Pet).ToList();

query1.ForEach(i => Console.WriteLine(i.Name));

#endregion

#region GroupBy 在集合中根据某个字段进行分组

var query = PetList.AsQueryable().GroupBy(pet => pet.Age);

foreach (var ageGroup in query)

{

Console.WriteLine("Pet s' Age group: {0} Number of pets: {1}",

ageGroup.Key, ageGroup.Count());

}

#endregion

#region 对age属性进行分组，并把name显示出来

IEnumerable
     
      
       > query3 =
      
     

PetList.AsQueryable().GroupBy(pet => pet.Age, pet => pet);

foreach (IGrouping
     
       petGroup in query3)
     

{

Console.WriteLine(petGroup.Key);

foreach (Pet pet in petGroup)

Console.WriteLine("  {0}", pet.Id+"..."+pet.Name);

}

#endregion

Console.ReadKey();

}

}