25. LINQ

· We can write LINQ (Language Integrated Query) as two ways: 1. Method Syntax & 2. Query Syntax (similar to database query)

· Some Name of LINQ: (To view 14 type LINQ code and example https://github.com/dotnet/try-samples/tree/main/101-linq-samples/src)

Namespace	Description
1. AggregateOperators	Contains operators for performing aggregate operations on collections, such as Sum(), Average(), and Count().
2. Conversions	Contains operators for converting between different types of collections, such as ToList(), ToArray(), and ToDictionary().
3. ElementOperations	Contains operators for performing operations on individual elements of a collection, such as First(), Last(), and Where().
4. Generators	Contains operators for generating new collections from existing collections, such as Range(), Repeat(), and Empty().
5. Groupings	Contains operators for grouping elements of a collection into groups, such as GroupBy() and ToLookup().
6. JoinOperations	Contains operators for joining two or more collections together, such as Join(), GroupJoin(), and LeftJoin().
7. Orderings	Contains operators for ordering elements of a collection, such as OrderBy() and OrderByDescending().
8. Partitions	Contains operators for partitioning a collection into smaller collections, such as Skip(), Take(), and Chunk().
9. Projections	Contains operators for projecting elements of a collection into new values, such as Select(), SelectMany(), and Cast().
10. Quantifiers	Contains operators for checking for the existence or absence of elements in a collection, such as Any(), All(), and Contains().
11. QueryExecution	Contains interfaces and classes for executing LINQ queries.
12. Restrictions	Contains operators for restricting the elements of a collection, such as Where() and SkipWhile().
13. SequenceOperations	Contains operators for performing operations on sequences of elements, such as Concat(), Union(), and Except().
14. SetOperations	Contains operators for performing set operations on collections, such as Intersect() and IsSubsetOf().

1. Aggregate Operators Example

// Method syntax
var sum = numbers.Sum();

// Query syntax
var sum = (from n in numbers select n).Sum();

Here’s the formatted code based on your provided examples:

2. Conversions Example

// Method syntax
var list = numbers.ToList();

// Query syntax
var list = (from n in numbers select n).ToList();

3. Element Operations Example

// Method syntax
var first = numbers.First();

// Query syntax
var first = (from n in numbers select n).First();

4. Generators Example

// Method syntax
var range = Enumerable.Range(1, 10);

// Query syntax
var range = from i in Enumerable.Range(1, 10) select i;

5. Grouping Example

// Method syntax
var groups = numbers.GroupBy(n => n % 2 == 0);

// Query syntax
var groups = from n in numbers group n by n % 2 == 0;

6. Join Operation Example

// Method syntax
var join = customers.Join(orders, c => c.Id, o => o.CustomerId, (c, o) => new { Customer = c, Order = o });

// Query syntax
var join = from c in customers join o in orders on c.Id equals o.CustomerId select new { Customer = c, Order = o };

7. Ordering Operations Example

// Method syntax
var ordered = numbers.OrderBy(n => n);

// Query syntax
var ordered = from n in numbers orderby n select n;

8. Partition Example

// Method syntax
var firstFive = numbers.Take(5);

// Query syntax
var firstFive = (from n in numbers select n).Take(5);

9. Projection Example

// Method syntax
var lengths = numbers.Select(n => n.ToString().Length);

// Query syntax
var lengths = from n in numbers select n.ToString().Length;

10. Quantifiers Example

// Method syntax
var hasNegative = numbers.Any(n => n < 0);

// Query syntax
var hasNegative = (from n in numbers where n < 0 select n).Any();

11. Query Executions Example

// Deferred execution
var query = from n in numbers where n <= 3 select n;
// Eager execution
var results = query.ToList();

12. Restrictions Example

// Method syntax
var filtered = numbers.Where(n => n <= 3);

// Query syntax
var filtered = from n in numbers where n <= 3 select n;

· Practice 3 Question:

Task 1: In this task, write a Linq query to print all students and their course name, like: “Jalaluddin, C#” “Hasan, Asp.net”

// Question
List<(int id, string name, double price)> courses = new List<(int id, string name, double price)>();
courses.Add((1, "C#", 8000));
courses.Add((2, "Asp.net", 30000));
 
List<(int id, string name, string address, int courseId)> students = new List<(int id, string name, string address, int courseId)>();
students.Add((3, "Jalaluddin", "Mirpur", 2));
students.Add((4, "Hasan", "Moghbazar", 1));
 
 
 
// Answer
// Query Syntax
var resultQuery = from x in students
                join y in courses
                on x.courseId equals y.id
                // where x.price > 10000
                select $"{x.name}, {y.name}";
foreach(var z in resultQuery)
    Console.WriteLine(z);
 
// Method Syntax
var resultMethod = students.Join(courses, x => x.courseId, y => y.id, (x, y) => $"{x.name}, {y.name}");
foreach(var z in resultMethod)
    Console.WriteLine(z);
 
 
// We can convert it into mssql query
SELECT c.name AS CourseName, s.name AS StudentName
FROM courses c
JOIN students s ON c.id = s.courseId
WHERE c.price > 10000;
 
SELECT COUNT(*) AS ResultCount
FROM courses c
JOIN students s ON c.id = s.courseId
WHERE c.price > 10000;

Task 2: In this task, write a Linq query to print all person data sorted according to name first and then by age (in case name is same). Print both name and age.

// Question
List<(int id, string name, int age)> persons = new List<(int id, string name, int age)>();
persons.Add((1, "Jalaluddin", 42));
persons.Add((2, "Hasan", 32));
persons.Add((3, "Maruf", 23));
 
// Answer
// Method Syntax
var sortedMethod = persons.OrderBy(x => x.name).ThenBy(x => x.age);
foreach (var x in sortedMethod)
    Console.WriteLine(x);
    
// Query Syntax
var sortedQuery = from x in persons orderby x.name, x.age select x;
foreach (var x in sortedQuery)
    Console.WriteLine(x);
// Convert it into sql
SELECT *
FROM persons
ORDER BY name, age;

Task 3: In this task, you have to print the names of fruits grouped by their last letter. Print the last letter and the fruits that belong to that letter.

// Question
string[] fruits = { "apple", "banana", "mango", "goava", "strawberry", "pineapple" };
 
// Answer
// Method Syntax
var groupResultMethod = fruits.GroupBy(x => x.Last());
foreach (var x in groupResultMethod)
{
    Console.WriteLine("Last letter is: " + x.Key);
    foreach (var y in x)
        Console.WriteLine(y);
}
 
// Query Syntax
 
// Method Syntax
var groupResultMethod = fruits.GroupBy(x => x.Last());
foreach (var x in groupResultMethod)
{
    Console.WriteLine("Last letter is: " + x.Key);
    foreach (var y in x)
        Console.WriteLine(y);
}
 
// Query Syntax
var groupResultQuery =
    from x in fruits
    group x by x[x.Length - 1] into g
    select (LastLetter: g.Key, Words: g);
foreach (var x in groupResultQuery)
{
    Console.WriteLine("Last letter is: " + x.LastLetter);
    foreach (var y in x.Words)
        Console.WriteLine(y);
}

Interview Question: Findout count, name and age from list where age>=25 && age⇐ 26

 
List<(string name, int age)> bios = new List<(string name, int age)>();
 
bios.Add(("MSA", 23));
bios.Add(("Shoyeb", 24));
bios.Add(("MSA2", 25));
bios.Add(("MSA3", 26));
bios.Add(("MSA4", 27));
bios.Add(("MSA5", 28));
 
// Method Query
var biosResultMethod = bios.Where(x => x.age >= 25 && x.age <= 26);
foreach (var x in biosResultMethod)
    Console.WriteLine("Name: {0}, Age: {1}", x.name, x.age);
Console.WriteLine("Total count: " + biosResultMethod.Count());
 
// Syntax Query
var biosResultQuery = from x in bios where x.age >= 25 && x.age <= 26 select x;
foreach (var x in biosResultQuery)
    Console.WriteLine("Name: {0}, Age: {1}", x.name, x.age);
Console.WriteLine("Total count: " + biosResultQuery.Count());