Zip, Join, GroupJoin

Zip

合并兩個序列，產生一個新的對象序列，但連接方式是一对一的（即序列1和第一项连接序列2的第一项），所以最终结果会在较短的序列处终止。

Zip在這裏不是壓縮的意思，而是拉鏈，意爲連接兩個序列

            Person magnus = new Person { Name = "Hedlund, Magnus" };
            Person terry = new Person { Name = "Adams, Terry" };
            Person charlotte = new Person { Name = "Weiss, Charlotte" };

            Pet barley = new Pet { Name = "Barley", Owner = terry };
            Pet boots = new Pet { Name = "Boots", Owner = terry };
            Pet whiskers = new Pet { Name = "Whiskers", Owner = charlotte };
            Pet daisy = new Pet { Name = "Daisy", Owner = magnus };

            List<Person> people = new List<Person> { magnus, terry, charlotte };
            List<Pet> pets = new List<Pet> { barley, boots, whiskers, daisy };

            var query = people.Zip(pets, (person, pet) => new { OwnerName = person.Name, Pet = pet.Name });

结果如下：

Hedlund, Magnus - Barley

Adams, Terry - Boots

Weiss, Charlotte - Whiskers

Join

合并兩個序列，產生一個新的對象序列，相當於内連接

            var query = people.Join(pets,
                            person => person,
                            pet => pet.Owner,
                            (person, pet) => new { OwnerName = person.Name, Pet = pet.Name });

            query = from person in people
                    join pet in pets on person equals pet.Owner
                    select new { OwnerName = person.Name, Pet = pet.Name };

結果如下：

Hedlund, Magnus - Daisy

Adams, Terry - Barley

Adams, Terry - Boots

Weiss, Charlotte - Whiskers

GroupJoin

合并兩個序列，產生一個分層的對象序列，序列中的每個元素都對應一個列表，這個方法在传统的关系数据库术语中没有直接的等效方法

            var query = people.GroupJoin(pets,
                            person => person,
                            pet => pet.Owner,
                            (person, petCollection) =>
                                new
                                {
                                    OwnerName = person.Name,
                                    Pets = petCollection.Select(pet => pet.Name)
                                });

            query = from person in people
                    join pet in pets on person equals pet.Owner into petCollection //其中petCollection是一個IEnumerable<Pet>
                    select new
                    {
                        OwnerName = person.Name,
                        Pets = petCollection.Select(pet => pet.Name)
                    };

結果如下：

> Hedlund, Magnus:

Daisy

> Adams, Terry:

Barley

Boots

> Weiss, Charlotte:

Whiskers