求一个linq的写法(join)

2011-07-13 01:56:46 318 阅读 AI 写同款 · GEO 优化AI 选题数据监测一键分发 ›

bearben2010 墨衍会员 · AI 创作全网分发关注 + 加入社区

LINQ join into static void QueryAnimalData() { Animal[] animals = new[] { new Animal{Name = "German Shepherd", Height = 25, Weight = ... 阅读详情



    public class Student

    {

        public String ID { get; set; }

        public String StuName { get; set; }

    }

    public class Grade

    {

        public String ID { get; set; }

        public String GrideName { get; set; }

    }



            //测试数据

            List<Student> tempStuList = new List<Student>() { 

                new Student(){ ID="001001", StuName="a"},

                new Student(){ ID="002001", StuName="b"},

                new Student(){ ID="002001", StuName="c"},

                new Student(){ ID="003001", StuName="d"},

                new Student(){ ID="001001", StuName="e"},

            };



            List<Grade> tempGradeList = new List<Grade>() { 

                new Grade(){ ID="001", GrideName = "g1"},

                new Grade(){ ID="002", GrideName = "g2"},

                new Grade(){ ID="003", GrideName = "g3"},

            };

说明一下:这里仅仅是讨论语法如何写,而不是讨论设计合理与否.这里只是举个例子
Stu.ID的前3位是年级ID,所以可以用下面的代码获取学生表与年级表的关联.这是一个很庆幸的例子.但是如果grade.ID是不定长的情况就无能为力了(不要管需求和实现是否合理,我只是寻求linq的语法).
我的问题是在做join的时候,linq能否写成 stu.ID.IndexOf(grade.ID) ==0类似的写法



            var a = from stu in tempStuList

                    join grade in tempGradeList

                    on stu.ID.Substring(0, 3) equals grade.ID

                    into tempGradeTable

                    from tempItem in tempGradeTable

                    select new { StuID = stu.ID, StuName = stu.StuName, GradeName = tempItem == null ? "" : tempItem.GrideName };

...全文

C# linq join 1、inner join SELECT 1 AS `C1`, `Extent1`.`code`, `Extent1`.`name` FROM `sg` AS `Extent1` INNER JOIN `cg` AS `Extent2` ON `Extent1`.`code` = `Extent2`.`code` **INNER JOIN ** 2、left outer join SELECT `Project1`.`id`, `Project1`.`code`, `Project1` 阅读详情

bearben2010

LINQ 8,492 成员 4,736 内容

+ 关注 + 加入社区

切换为时间正序

threenewbee 2011-07-13

打赏
举报

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;



namespace ConsoleApplication1

{

    class Program

    {

        public class Student

        {

            public String ID { get; set; }

            public String StuName { get; set; }

        }

        public class Grade

        {

            public String ID { get; set; }

            public String GrideName { get; set; }

        }



        static void Main(string[] args)

        {

            List<Student> tempStuList = new List<Student>() { 

                new Student(){ ID="001001", StuName="a"},

                new Student(){ ID="002001", StuName="b"},

                new Student(){ ID="002001", StuName="c"},

                new Student(){ ID="003001", StuName="d"},

                new Student(){ ID="003001", StuName="e"},

            };



            List<Grade> tempGradeList = new List<Grade>() { 

                new Grade(){ ID="001", GrideName = "g1"},

                new Grade(){ ID="002", GrideName = "g2"},

                new Grade(){ ID="003", GrideName = "g3"},

            };



            var a = from stu in tempStuList

                    select new { StuID = stu.ID, StuName = stu.StuName, GradeName = (tempGradeList.Where(x => stu.ID.IndexOf(x.ID) == 0).Count() > 0 ? tempGradeList.Where(x => stu.ID.IndexOf(x.ID) == 0).First().GrideName : "") };



            a.ToList().ForEach(x => Console.WriteLine(x));



        }

    }

}

threenewbee 2011-07-13

打赏
举报

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;



namespace ConsoleApplication1

{

    class Program

    {

        public class Student

        {

            public String ID { get; set; }

            public String StuName { get; set; }

        }

        public class Grade

        {

            public String ID { get; set; }

            public String GrideName { get; set; }

        }



        static void Main(string[] args)

        {

            List<Student> tempStuList = new List<Student>() { 

                new Student(){ ID="001001", StuName="a"},

                new Student(){ ID="002001", StuName="b"},

                new Student(){ ID="002001", StuName="c"},

                new Student(){ ID="003001", StuName="d"},

                new Student(){ ID="001001", StuName="e"},

            };



            List<Grade> tempGradeList = new List<Grade>() { 

                new Grade(){ ID="001", GrideName = "g1"},

                new Grade(){ ID="002", GrideName = "g2"},

                new Grade(){ ID="003", GrideName = "g3"},

            };



            var a = from stu in tempStuList

                    select new { StuID = stu.ID, StuName = stu.StuName, GradeName = (tempGradeList.Where(x => stu.ID.IndexOf(x.ID) == 0).SingleOrDefault().GrideName) };



            a.ToList().ForEach(x => Console.WriteLine(x));



        }

    }

}

bearben2010 2011-07-13

打赏
举报

Tim老兄能给写一下么?我linq不熟,一时半会写不出来.呵呵,谢谢

宝_爸 2011-07-13

打赏
举报

这样是可以的



    class GradeComparer : IEqualityComparer<string>

    {

        public bool Equals(string b1, string b2)

        {

            string stuId = b1.Length < b2.Length ? b2 : b1;

            string gradeId = b1.Length < b2.Length ? b1 : b2;



            return stuId.StartsWith(gradeId);            

        }





        public int GetHashCode(string bx)

        {

            return 1;  //返回同样的值，在Equals中进行真正的比较。可能效率会稍差。如果GetHashCode返回不同的值，Equals不会被调用。

        }

    }





            GradeComparer gradeComparer = new GradeComparer();

            var query = tempStuList.Join(tempGradeList,

                                s => s.ID,                  

                                g => g.ID,

                                (s, g) => new { ID = s.ID, Name = s.StuName, GID = g.ID, GName = g.GrideName},

                                gradeComparer);



            foreach (var obj in query)

            {

                Console.WriteLine(obj.ID, obj.Name, obj.GID, obj.GName);

            }

q107770540 2011-07-13

打赏
举报

你既然使用了JOIN 就要遵守JOIN的语法使用 equals关键字

如果你一定要使用 stu.ID.IndexOf(grade.ID) ==0 类似这样的写法

你可以使用 WHERE关键字结合 ANY()方法来实现

宝_爸 2011-07-13

打赏
举报

下面是我的实验，目前不行，Equals不被调用。拿出来抛砖引玉。



    class GradeComparer : IEqualityComparer<string>

    {

        public bool Equals(string b1, string b2)

        {

            string stuId = b1.Length < b2.Length ? b2 : b1;

            string gradeId = b1.Length < b2.Length ? b1 : b2;



            return stuId.StartsWith(gradeId);            

        }





        public int GetHashCode(string bx)

        {

            return bx.GetHashCode();

        }

    }



            GradeComparer gradeComparer = new GradeComparer();

            var query = tempStuList.Join(tempGradeList,

                                s => s.ID,                  

                                g => g.ID,

                                (s, g) => new { ID = s.ID, Name = s.StuName, GID = g.ID, GName = g.GrideName},

                                gradeComparer);



            foreach (var obj in query)

            {

                Console.WriteLine(obj.ID, obj.Name, obj.GID, obj.GName);

            }

宝_爸 2011-07-13

打赏
举报

普通的join也不行
Enumerable.Join<TOuter, TInner, TKey, TResult> Method (IEnumerable<TOuter>, IEnumerable<TInner>, Func<TOuter, TKey>, Func<TInner, TKey>, Func<TOuter, TInner, TResult>)
Func<TOuter, TKey>制定Student的key，是访问不到Inner中的对象的。

可以试一试

Enumerable.Join<TOuter, TInner, TKey, TResult> Method (IEnumerable<TOuter>, IEnumerable<TInner>, Func<TOuter, TKey>, Func<TInner, TKey>, Func<TOuter, TInner, TResult>, IEqualityComparer<TKey>)

IEqualityComparer中进行比较

threenewbee 2011-07-13

打赏
举报

使用 Join() 方法，LINQ 表达式貌似不行。

HDNGO 2011-07-13

打赏
举报

你不是用Substring解决了？

bearben2010 2011-07-13

打赏
举报

我想要的是on stu.ID.IndexOf(grade.ID) == 0类似这样的写法,但是这在Linq中是语法错误

HDNGO 2011-07-13

打赏
举报

你现在写的有什么问题？

求一个linq的写法(join)

相关推荐