LINQ学习（四）：From子句

from 子句中引用的数据源的类型必须为 IEnumerable、IEnumerable<T> 或一种派生类型（如 IQueryable<T>）。

 

1.复合from子句

说明：如果一个数据源里面又包含了一个或多个集合列表，那么应该使用复合的from子句来进行查询。

查询分数小于60分学生的姓名和分数：

        class Student
        {
            public string Name { get; set; }
            public List<int> Scores { get; set; }
        }
        static void Main(string[] args)
        {
            List<Student> students = new List<Student>{
               new Student {Name="Terry", Scores=new List<int> {97, 72, 81, 60}},
               new Student {Name="AI", Scores=new List<int> {75, 84, 91, 39}},
               new Student {Name="Wade", Scores=new List<int> {88, 94, 65, 85}},
               new Student {Name="Tracy", Scores=new List<int>{97, 89, 85, 82}},
               new Student {Name="Kobe", Scores=new List<int> {35, 72, 91, 70}} 
            };
            var query = from student in students
                        from score in student.Scores
                        where score < 60
                        select new { name = student.Name, score };
            foreach (var student in query)
            {
                Console.WriteLine("{0},{1}", student.name, student.score);
                //AI,39
                //Kobe,35
            }
            Console.ReadKey();
        }

 

2.使用多个 from 子句执行联接

说明：from 子句。

交叉联接：

            char[] char1 = { 'A', 'B', 'C' };
            char[] char2 = { 'a', 'b', 'c' };
            var query =
                from c1 in char1
                from c2 in char2
                select new { c1, c2 };
            Console.WriteLine("交叉联接:");
            foreach (var result in query)
            {
                Console.WriteLine("{0}", result);
                //交叉联接:
                //{ c1 = A, c2 = a }
                //{ c1 = A, c2 = b }
                //{ c1 = A, c2 = c }
                //{ c1 = B, c2 = a }
                //{ c1 = B, c2 = b }
                //{ c1 = B, c2 = c }
                //{ c1 = C, c2 = a }
                //{ c1 = C, c2 = b }
                //{ c1 = C, c2 = c }
            }

 

  

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