Question

我修改了此代码（在灰色部分下方），原始代码位于https://www.youtube.com/watch?v=gwD9awr3NNo

有点复杂。

问题在于代码的这一部分（下面完整的代码）：

var groupJoin =
                    from owner in owners
                    orderby owner.OwnerID
                    join animal in animals on owner.OwnerID
                    equals animal.OwnerID into ownerGroup
                    select new
                    {
                        Owner = owner.Name,
                        Animals = from owner2 in ownerGroup
                              select owner2
                    };

ownerGroup不应同时包含所有者和动物信息（这是一个联接，联接意味着它应同时包含两者）。

因此，假设这是真的，是什么导致动物被限制为仅来自动物的信息（没有拥有者的信息）？我推论的方法是： Intellisense显示x（请参阅下面的完整代码）。只拥有动物类的信息

查看行：//Console.WriteLine("* {0}“，x.Name）; <-不起作用

namespace LinqTutorialByDerekBanas
{

    class Program
    {

        static void Main(string[] args)
        {

            bool RunMe;

            QueryAnimalData();
        }

        class Animal
        {
            public string AnimalName { get; set; }
            public double Weight { get; set; }
            public double Height { get; set; }
            public int OwnerID { get; set; }

            public Animal(string name = "No Name",
                double weight = 0,
                double height = 0)
            {
                AnimalName = name;
                Weight = weight;
                Height = height;
            }

            public override string ToString()
            {
                return string.Format("{0} weighs {1}lbs and is {2} inches tall",
                    AnimalName, Weight, Height);
            }
        }


        class Owner
        {
                public string Name { get; set; }
                public int OwnerID { get; set; }
        }

            static void QueryAnimalData()
            {
                Animal[] animals = new[]
                {
                    new Animal{AnimalName = "German Shepherd",
                    Height = 25,
                    Weight = 77,
                    OwnerID = 1},
                    new Animal{AnimalName = "Chihuahua",
                    Height = 7,
                    Weight = 4.4,
                    OwnerID = 2},
                    new Animal{AnimalName = "Saint Bernard",
                    Height = 30,
                    Weight = 200,
                    OwnerID = 3},
                    new Animal{AnimalName = "Pug",
                    Height = 12,
                    Weight = 16,
                    OwnerID = 1},
                    new Animal{AnimalName = "Beagle",
                    Height = 15,
                    Weight = 23,
                    OwnerID = 2}
                };

                Owner[] owners = new[]
                {
                    new Owner{Name = "Doug Parks",
                    OwnerID = 1},
                    new Owner{Name = "Sally Smith",
                    OwnerID = 2},
                    new Owner{Name = "Paul Brooks",
                    OwnerID = 3}
                };



                // Create a group inner join
                // Get all animals and put them in a
                // newly created owner group if their
                // IDs match the owners ID 
                var groupJoin =
                    from owner in owners
                    orderby owner.OwnerID
                    join animal in animals on owner.OwnerID
                    equals animal.OwnerID into ownerGroup
                    select new
                    {
                        Owner = owner.Name,
                        Animals = from owner2 in ownerGroup
                                  select owner2
                    };

                int totalAnimals = 0;

                foreach (var ownerGroup in groupJoin)
                {
                    Console.WriteLine(ownerGroup.Owner);
                    foreach (var x in ownerGroup.Animals)
                    {
                        totalAnimals++;
                        Console.WriteLine("* {0}", x.AnimalName);
                        //Console.WriteLine("* {0}", x.Name);  <-- DOES NOT WORK

                    }
                }
            }

     }
}

Answer 1

join ... into是GroupJoin的查询语法。组联接是一种LINQ构造，它使一个项目与一组相关项目相关（例如，使用1到许多外键）。

因此在查询中，ownerGroup（我将其命名为animaljoin或aj）是{{1}与单个所有者相关的animals的集合}。

行

OwnerID

对我来说毫无意义-为什么您要重命名Animals = from owner2 in ownerGroup select owner2 owner2？由于Animals是用词不当，实际上是一组ownerGroup，因此，我不确定您打算在这里做什么。

考虑实际实现组联接的扩展方法（这是animal版本，但Enumerable与此类似）：

Queryable

这结合了两个序列（public static IEnumerable<TResult> GroupJoin<TOuter,TInner,TKey,TResult> ( this IEnumerable<TOuter> outer, IEnumerable<TInner> inner, Func<TOuter,TKey> outerKeySelector, Func<TInner,TKey> innerKeySelector, Func<TOuter,IEnumerable<TInner>,TResult> resultSelector);和outer），使用两个lambda提取匹配的键，然后为每个inner发送outer和所有匹配的{{ 1}}）outer到结果lambda。

Linq Join似乎没有完整联接的数据

1 个答案: