1.查詢語法?

Query Syntax:

from <range variable> in <IEnumerable<T> or IQueryable<T> Collection><Standard Query Operators> <lambda expression><select or groupBy operator> <result formation>

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// string collection IList<string> stringList = new List<string>() { "C# Tutorials","VB.NET Tutorials","Learn C++","MVC Tutorials" ,"Java" };// LINQ Query Syntax var result = from s in stringListwhere s.Contains("Tutorials") select s;

查詢語法以From開頭，后面緊跟著Range veriable變量，From從句像這樣的結構"From?rangeVariableName?in?IEnumerablecollection"，意思是從集合的每個對象中獲取，它有點像foreach循環，

?foreach(Student s in studentList)

在From從句之后，我們可以使用不同的標準查詢運算符來過濾、分類和聯合集合里面的元素，大概有50個標準查詢操作

一般以Select 或Group從句結尾，Select從句用來構建數據，你可以查詢全部對象或者它的幾個屬性。

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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 } };// LINQ Query Syntax to find out teenager students var teenAgerStudent = from s in studentListwhere s.Age > 12 && s.Age < 20select s;

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LINQ Method Syntax

// string collection IList<string> stringList = new List<string>() { "C# Tutorials","VB.NET Tutorials","Learn C++","MVC Tutorials" ,"Java" };// LINQ Query Syntax var result = stringList.Where(s => s.Contains("Tutorials"));

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// Student collection 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 } };// LINQ Method Syntax to find out teenager students var teenAgerStudents = studentList.Where(s => s.Age > 12 && s.Age < 20).ToList<Student>();

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Standard Query Operators:

Standard Query Operators in Query Syntax:

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Standard Query Operators in Method Syntax:

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標準查詢操作根據功能分類?

ClassificationStandard Query Operators

Filtering（篩選）	Where, OfType
Sorting（排序）	OrderBy, OrderByDescending, ThenBy, ThenByDescending, Reverse
Grouping（分組）	GroupBy, ToLookup
Join（連接）	GroupJoin, Join
Projection（投影）	Select, SelectMany
Aggregation（聚集）	Aggregate, Average, Count, LongCount, Max, Min, Sum
Quantifiers（量詞）	All, Any, Contains
Elements（元素）	ElementAt, ElementAtOrDefault, First, FirstOrDefault, Last, LastOrDefault, Single, SingleOrDefault
Set（集合）	Distinct, Except, Intersect, Union
Partitioning（分割）	Skip, SkipWhile, Take, TakeWhile
Concatenation（連接）	Concat
Equality	SequenceEqual
Generation	DefaultEmpty, Empty, Range, Repeat
Conversion	AsEnumerable, AsQueryable, Cast, ToArray, ToDictionary, ToList

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轉載于:https://www.cnblogs.com/lanpingwang/p/6602024.html

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