Linq in GroupBy GroupJoin

还是上一份的代码例子：

  public class Person
    {
        public int ID { get; set; }

        public string Name { get; set; }

        public int Age { get; set; }       
    }
    public class Dog
    {
        public int ID { get; set; }
        public string Name { get; set; }
        public int PersonID { get; set; }
    }
    public class DogClothes
    {
        public int ID { get; set; }
        public string Name { get; set; }
        public int DogID { get; set; }
    }
    public class ActionPerson
    { 
        public List<Person> GetPersons()
        {
            List<Person> list = new List<Person>();
            for (var i = 0; i < 10; i++)
            {
                Person p = new Person {ID=i+1, Name = "hongda" + (i + 1), Age = 26 + i };
                list.Add(p);
            }
            return list;
        }
        public List<Dog> GetDogs()
        {
            List<Dog> dogs = new List<Dog>();
            for (var i = 1; i < 15; i++)
            {
                Dog dog = new Dog { ID = i, Name = "dogs" + i, PersonID = (i %5)+1 };
                dogs.Add(dog);
            }
            return dogs;
        }
        public List<DogClothes> GetDogClotheses()
        {
            List<DogClothes> DogClothes = new List<DogClothes>();
            for (var i = 1; i < 13; i++)
            {
                DogClothes clothes = new DogClothes() { ID = i, Name = "DogClothes" + i, DogID = (i % 4) + 2 };
                DogClothes.Add(clothes);
            }
            return DogClothes;
        }
        public void Show<T>(List<T> list)
        {
            foreach (var l in list)
            {
                ShowObj(l);
            }
        }
        public void ShowObj<T>(T data)
        {
            Type t = data.GetType();
            PropertyInfo[] infos = t.GetProperties();
            StringBuilder strBuilder = new StringBuilder();
            foreach (var p in infos)
            {
                object value = p.GetValue(data, null);
                string name = p.Name.ToString();
                strBuilder.Append(name + ":" + value + ",");
            }
            Console.WriteLine(strBuilder.ToString());
        }
        public void ShowArray<T>(T[] arr)
        {
            foreach (var t in arr)
            {
                Console.WriteLine(t.ToString());
            }
        }
    }

 操作：

 static void Main(string[] args)
        {
            ActionPerson ap = new ActionPerson();
            List<Person> list = ap.GetPersons();
            List<Dog> dogs = ap.GetDogs();
            List<DogClothes> dogClotheses = ap.GetDogClotheses();
            int[] arr = { 2, 3, 4, 5 };
            var result = list.Where(q => arr.Contains(q.ID));
            ap.Show(result.ToList ());
            Console.WriteLine("=============================");
            var result2 = list.Where(q => dogs.Select(o => o.PersonID).Contains(q.ID));
            ap.Show(result2.ToList());
            Console.ReadLine();
        }

 var result = list.Select(o => o.Name);
            ap.Show(result.ToList());

再看

var result = list.Select(o => o.Name);
            ap.ShowArray(result.ToArray());

可以看出Select(o=>o.Name) 返回的是数组

返回对象

   var result = list.Select(p => new { ID = p.ID, p.Name, p.Age });
            ap.Show(result.ToList ());

对象数组

 var result = list.Select(p => new { ID = p.ID, p.Name, p.Age });
            ap.ShowArray(result.ToArray());

Group Join

 var result = from a in list
                         join b in dogs on a.ID equals b.PersonID into c
                         select new { a, c };
            ap.Show(result.ToList());

  var result = from a in list
                         join b in dogs on a.ID equals b.PersonID into c
                         select new { a, c };
            foreach (var r in result)
            {
                ap.ShowObj(r.a);
                ap.Show(r.c.ToList());
                Console.WriteLine("========================================");
            }

            var result = list.GroupJoin(dogs, a => a.ID, b => b.PersonID, (a, c) => new {a,c });

结果同上

c还有一些其他的属性 

GroupBy

  var result = from b in dogs group b by b.PersonID into g select new { g.Key, Count = g.Count(), Member = g };
            foreach (var r in result)
            {
                Console.WriteLine(r.Key + "," + r.Count + ",");
                foreach (var m in r.Member)
                {
                    ap.ShowObj(m);
                }
                Console.WriteLine("=================================");
            }

             var result = (from b in dogs select b).GroupBy(q => q.PersonID).Select(q => new { q.Key, Count = q.Count(), Member = q });

结果同上