LINQ Lessons

In our recent project, we came across many situations where we had to write queries on our objects in the UI tier. Few of them are give below.

I am taking here the movie class to explain different Linq queries.

public class Movie
{

     public int ID {get; set;}
     public string Title {get; set;}
  public string Director {get; set;}
     public int Genre {get; set;}
     public int RunTime {get; set;}
     public DateTime ReleaseDate {get; set;}

     public decimal Budget{get; set;}

}

public List GetMovies()
{
return new List {
new Movie{Title="Rocky", Director="Alex", Genre=1, RunTime=180, ReleaseDate ="01/01/1990"},
new Movie{Title="Return of the Devil", Director="Michael", Genre=2, RunTime=80, ReleaseDate ="01/01/1998"},
new Movie{Title="Warriors", Director="Phil", Genre=3, RunTime=120, ReleaseDate ="01/01/1991"},
new Movie{Title="Love", Director="Kevin", Genre=4, RunTime=120, ReleaseDate ="01/01/1992"},
new Movie{Title="Live Forever", Director="Leonardo", Genre=5, RunTime=120, ReleaseDate ="01/01/1997"},
new Movie{Title="War", Director="Adams", Genre=6, RunTime=130, ReleaseDate ="01/01/2001"},
new Movie{Title="Crimes of the City", Director="Ricky", Genre=6, RunTime=130, ReleaseDate ="01/01/1995"},
new Movie{Title="Street Fighters", Director="Andrew", Genre=6, RunTime=130, ReleaseDate ="01/01/1995"},
new Movie{Title="Violence", Director="David", Genre=6, RunTime=130, ReleaseDate ="01/01/1998"},
new Movie{Title="College Days", Director="Clarke", Genre=4, RunTime=140, ReleaseDate ="01/01/1997"},

};
}

Query: Get all movies from generic movies collection.

var movies = GetMovies();
var query = from m in movies select m;

Query : Return a new projection containing Title and Genre.

var movies = GetMovies();
var query = from m in movies select new {m.Title, m.Genre};
or
var query = from m in movies select new {MovieTitle = m.Title, MovieGenre = m.Genre};

Query: Return all movies order by Title

var movies = GetMovies();
var query = from m in movies order by m.Title descending select m

Query: Adding a filter to a Linq query.

var movies = GetMovies();
var query = from m in movies where m.Genre=5 select m;

Query: Data Grouping

var movies = GetMovies();
var query = from m in movies group by m.Genre into g
            select new {Genre = g.key, Count = g.Count} 
            

Query : Linq Operators

var movies = GetMovies();
movies.Max(m=>m.RunTime)
movies.Min(m=>m.RunTim)
movies.Average(m=>m.RunTime)

Query: Linq Joins

var moveis = GetMovies();
var genres = GetGenres();

var query = from m in movies Join g in genres On m.Genre Equals g.ID
            select new {Title = m.Title, Genre = g.Name}

Query: Left Join
All movies from movies object irrespecitive of having a genre or not.

var m = from m in movies join g in generes on m.Genre equals g.ID into MovGen
              from MovGenJ in MovGen.DefaultIfEmpty()
             select new {Title = m.Title, Genre = g.Name}

Query: Paging using Linq

var query = (from m in movies Join g in generes On m.Genre Equals g.ID 
             select new {Title = m.Title, Genre = g.Name}).Skip(10).Take(10);

Query: For loop in Linq

var m = movies.ForEach(m =>m.Budget = GetMoviesBudget(m.ID))