مثال هایی از LINQ – آموزش LINQ

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تصویر sample-linq-queries_11139 مثال هایی از LINQ - آموزش LINQ

مثال هایی از LINQ

در این بخش از دو مجموعه Student و Standard که در زیر مشاهده می کنید، برای نوشتن کوئری LINQ استفاده خواهیم کرد:

IList<Student> studentList = new List<Student>() { 
    new Student() { StudentID = 1, StudentName = "John", Age = 18, StandardID = 1 } ,
    new Student() { StudentID = 2, StudentName = "Steve",  Age = 21, StandardID = 1 } ,
    new Student() { StudentID = 3, StudentName = "Bill",  Age = 18, StandardID = 2 } ,
    new Student() { StudentID = 4, StudentName = "Ram" , Age = 20, StandardID = 2 } ,
    new Student() { StudentID = 5, StudentName = "Ron" , Age = 21 } 
};
IList<Standard> standardList = new List<Standard>() { 
    new Standard(){ StandardID = 1, StandardName="Standard 1"},
    new Standard(){ StandardID = 2, StandardName="Standard 2"},
    new Standard(){ StandardID = 3, StandardName="Standard 3"}
};

IList<Student> studentList = new List<Student>() {

new Student() { StudentID = 1, StudentName = "John", Age = 18, StandardID = 1 } ,

new Student() { StudentID = 2, StudentName = "Steve", Age = 21, StandardID = 1 } ,

new Student() { StudentID = 3, StudentName = "Bill", Age = 18, StandardID = 2 } ,

new Student() { StudentID = 4, StudentName = "Ram" , Age = 20, StandardID = 2 } ,

new Student() { StudentID = 5, StudentName = "Ron" , Age = 21 }

};

IList<Standard> standardList = new List<Standard>() {

new Standard(){ StandardID = 1, StandardName="Standard 1"},

new Standard(){ StandardID = 2, StandardName="Standard 2"},

new Standard(){ StandardID = 3, StandardName="Standard 3"}

};

Select چندگانه و عملگر Where

var studentNames = studentList.Where(s => s.Age > 18)
                              .Select(s => s)
                              .Where(st => st.StandardID > 0)
                              .Select(s => s.StudentName);

var studentNames = studentList.Where(s => s.Age > 18)

.Select(s => s)

.Where(st => st.StandardID > 0)

.Select(s => s.StudentName);

خروجی:

Steve
Ram

Steve

Ram

در مثال زیر کوئری ما یک Enumerable از شیء anonymous باز میگرداند که فقط شامل خاصیت StudentName است:

var teenStudentsName = from s in studentList
                       where s.age > 12 && s.age < 20
                       select new { StudentName = s.StudentName };
teenStudentsName.ToList().ForEach(s => Console.WriteLine(s.StudentName));

var teenStudentsName = from s in studentList

where s.age > 12 && s.age < 20

select new { StudentName = s.StudentName };

teenStudentsName.ToList().ForEach(s => Console.WriteLine(s.StudentName));

خروجی:

John
Bill

John

Bill

گروه بندی

در مثال زیر لیست دانش آموزان را توسط خاصیت StandardID گروه بندی می کنیم:

var studentsGroupByStandard = from s in studentList
                              group s by s.StandardID into sg
                              orderby sg.Key 
                                    select new { sg.Key, sg };
foreach (var group in studentsGroupByStandard)
{
    Console.WriteLine("StandardID {0}:", group.Key);
    
    group.sg.ToList().ForEach(st => Console.WriteLine(st.StudentName ));
}

var studentsGroupByStandard = from s in studentList

group s by s.StandardID into sg

orderby sg.Key

select new { sg.Key, sg };

foreach (var group in studentsGroupByStandard)

{

Console.WriteLine("StandardID {0}:", group.Key);

group.sg.ToList().ForEach(st => Console.WriteLine(st.StudentName ));

}

خروجی:

StandardID 0:
Ron
StandardID 1:
John
Steve
StandardID 2:
Bill
Ram

StandardID 0:

Ron

StandardID 1:

John

Steve

StandardID 2:

Bill

Ram

اگر به لیست تعریف شده در بالا توجه کنید متوجه می شوید که Ron هیچ StandardID ندارد به خاطر همین در گروه StandardID 0 قرار گرفته است (چون مقدار پیشفرض int صفر است). برای رفع این مورد می توانید از عملگر Where مانند نمونه زیر استفاده کنید:

var studentsGroupByStandard = from s in studentList
                              where s.StandardID > 0
                              group s by s.StandardID into sg
                              orderby sg.Key 
                                    select new { sg.Key, sg };

var studentsGroupByStandard = from s in studentList

where s.StandardID > 0

group s by s.StandardID into sg

orderby sg.Key

select new { sg.Key, sg };

خروجی:

StandardID 1:
John
Steve
StandardID 2:
Bill
Ram

StandardID 1:

John

Steve

StandardID 2:

Bill

Ram

Left Outer Join در LINQ

با استفاده از Left Outer Join می توانیم دانش آموزان را در هر استاندارد قرار دارند را نمایش دهیم:

var studentsGroup = from stad in standardList
                    join s in studentList
                    on stad.StandardID equals s.StandardID
                        into sg
                        select new { 
                                        StandardName = stad.StandardName, 
                                        Students = sg 
                                    };
foreach (var group in studentsGroup)
{
    Console.WriteLine(group.StandardName);
    group.Students.ToList().ForEach(st => Console.WriteLine(st.StudentName));
}

var studentsGroup = from stad in standardList

join s in studentList

on stad.StandardID equals s.StandardID

into sg

select new {

StandardName = stad.StandardName,

Students = sg

};

foreach (var group in studentsGroup)

{

Console.WriteLine(group.StandardName);

group.Students.ToList().ForEach(st => Console.WriteLine(st.StudentName));

}

خروجی:

Standard 1:
John
Steve
Standard 2:
Bill
Ram
Standard 3:

Standard 1:

John

Steve

Standard 2:

Bill

Ram

Standard 3:

مرتب‌سازی

در نمونه زیر لیست دانش آموزان به صورت صعودی و توسط خاصیت StandardID و Age مرتب می شود:

var sortedStudents = from s in studentList
                        orderby s.StandardID, s.age
                        select new { 
                                StudentName = s.StudentName, 
                                Age = s.age, 
                                StandardID = s.StandardID };
sortedStudents.ToList().ForEach(s => Console.WriteLine("Student Name: {0}, Age: {1}, StandardID: {2}", s.StudentName, s.Age , s.StandardID));

var sortedStudents = from s in studentList

orderby s.StandardID, s.age

select new {

StudentName = s.StudentName,

Age = s.age,

StandardID = s.StandardID };

sortedStudents.ToList().ForEach(s => Console.WriteLine("Student Name: {0}, Age: {1}, StandardID: {2}", s.StudentName, s.Age , s.StandardID));

خروجی:

Student Name: Ron, Age: 21, StandardID: 0
Student Name: John, Age: 18, StandardID: 1
Student Name: Steve, Age: 21, StandardID: 1
Student Name: Bill, Age: 18, StandardID: 2
Student Name: Ram, Age: 20, StandardID: 2

Student Name: Ron, Age: 21, StandardID: 0

Student Name: John, Age: 18, StandardID: 1

Student Name: Steve, Age: 21, StandardID: 1

Student Name: Bill, Age: 18, StandardID: 2

Student Name: Ram, Age: 20, StandardID: 2

Inner Join در LINQ

var studentWithStandard = from s in studentList
                          join stad in standardList
                          on s.StandardID equals stad.StandardID 
                          select new { 
                                  StudentName = s.StudentName, 
                                  StandardName = stad.StandardName 
                              };
studentWithStandard.ToList().ForEach(s => Console.WriteLine("{0} is in {1}", s.StudentName, s.StandardName  ));

var studentWithStandard = from s in studentList

join stad in standardList

on s.StandardID equals stad.StandardID

select new {

StudentName = s.StudentName,

StandardName = stad.StandardName

};

studentWithStandard.ToList().ForEach(s => Console.WriteLine("{0} is in {1}", s.StudentName, s.StandardName ));

خروجی:

John is in Standard 1
Steve is in Standard 1
Bill is in Standard 2
Ram is in Standard 2

John is in Standard 1

Steve is in Standard 1

Bill is in Standard 2

Ram is in Standard 2

کوئری تو در تو (Nested Query)

var nestedQueries = from s in studentList
                    where s.age > 18 && s.StandardID == 
                        (from std in standardList
                        where std.StandardName == "Standard 1"
                        select std.StandardID).FirstOrDefault()
                            select s;
nestedQueries.ToList().ForEach(s => Console.WriteLine(s.StudentName));