3. Linq操作符

条件操作符 where

映射操作符 select

LINQ query syntax must end with a Select or GroupBy clause

public class Student{
    public int StudentID { get; set; }
    public string StudentName { get; set; }
    public int Age { get; set; }
}


IList<Student> studentList = new List<Student>() {
    new Student() { StudentID = 1, StudentName = "John" },
    new Student() { StudentID = 2, StudentName = "Moin" },
    new Student() { StudentID = 3, StudentName = "Bill" },
    new Student() { StudentID = 4, StudentName = "Ram" },
    new Student() { StudentID = 5, StudentName = "Ron" }
};

//只是查询姓名
var selectResult = from s in studentList
                   select s.StudentName;

IList<Student> studentList = new List<Student>() {
    new Student() { StudentID = 1, StudentName = "John", Age = 13 } ,
    new Student() { StudentID = 2, StudentName = "Moin",  Age = 21 } ,
    new Student() { StudentID = 3, StudentName = "Bill",  Age = 18 } ,
    new Student() { StudentID = 4, StudentName = "Ram" , Age = 20 } ,
    new Student() { StudentID = 5, StudentName = "Ron" , Age = 15 }
};

//这里面可以针对不同条件对数据做不同处理
// returns collection of anonymous objects with Name and Age property
var selectResult = from s in studentList
                   select new { Name = "Mr. " + s.StudentName, Age =s.Age==15?1:s.Age };

// iterate selectResult
foreach (var item in selectResult)
    Console.WriteLine("Student Name: {0}, Age: {1}", item.Name, item.Age);

分割操作符 Partition operators

Take, Skip, TakeWhile and SkipWhile methods to partition the input sequence .You can get a slice of the input sequence as the output sequence.

排序操作符 Ordering operators

The orderby keyword, along with descending, and the OrderBy, ThenBy, OrderbyDescending and ThenByDescending LINQ queries are used to sort data output.

分组操作符 Grouping operators

The GroupBy and into operators organize a sequence into buckets.

集合操作符 Set Operators

这些操作符提供对多个集合的数据对比, 提供不同集合直接的交集,并集,不重复和差异的

转换操作符 Conversion operators

转化成Array List Dictionary 或指定的元素类型

元素操作符 Element operators

The methods First, FirstOrDefault, Last, LastOrDefault, and ElementAt retrieve elements based on the position of that element in the sequence.

• FirstOrDefault 返回第一个元素,当没有元素的时候,返回对应类型的默认值;

生成操作符 Generate sequences

量化操作符 Quantifying members

all any

聚合操作符 Aggregator operators

count

序列操作符 Sequence operations

懒查询 Eager and lazy query execution

Join 操作符 Join operations