Saturday, October 13, 2012
"Language Integrated Query (LINQ, pronounced "link") is a Microsoft .NET Framework component that adds native data querying capabilities to.NET languages, although ports exist for Java, PHP, JavaScript, and ActionScript". wikipedia
Linq provides some C# standard method that you can call them by method syntax instead of query syntax in C# development environment, very useful for retrieving information from databases by formulating queries, questions, expressed in the language. most used of those methods are Select, Join, Where, Group, Max, Min, …
Example one
create this class and its definition
public class Profile
{
public string Name { get; set; }
public string LastName { get; set; }
public int Age { get; set; }
}
And add this Service class :
public class ProfileService
{
public List<string> Operation()
{
var profiles = new List<Profile>
{
new Profile {Age = 23, Name = "Ehsan", LastName = "Ghanbari"},
new Profile {Age = 30, Name = "Tom", LastName = "Miles"}
};
var query = from f in profiles where f.Age == 23 select f.Name;
return query.ToList();
}
This query returns the Name of person with 23 years old, test below queries too and sees the result
var query2 = from f in profiles orderby f.Age ascending select f;
var query3 = from f in profiles where f.Name == "Tom" select f;
var query4 = from f in profiles where f.Age > 25 select f;
var query5 = from f in profiles where f.LastName.StartsWith("M") select f;
var query6 = profiles.Single(c => c.Age == 40);
var query7 = profiles.SingleOrDefault();
var query8 = profiles.Select(c => c.Name).ToList();
Example two
Book class :
public class Book
{
public int BookId { get; set; }
public string Name { get; set; }
public bool IsPublished { get; set; }
}
and Author class
public class Author
{
public int AuthorId { get; set; }
public string Name { get; set; }
public Book Book { get; set; }
}
(Notice that every author could have many books )
Create a Service class to initialize Book and Authors :
public class InitializerClass
{
public void Initialize()
{
var books = new List<Book>
{
new Book {BookId = 1, Name = "DDD", IsPublished = true,PulishDate=DateTime.Now},
new Book {BookId = 2, Name = "Design Pattern", IsPublished = false,PulishDate=DateTime.Now}
};
var authors = new List<Author>
{
new Author
{
AuthorId = 1,
Name = "Eric",
Book = new Book {BookId = 1, Name = "DDD", IsPublished = true}
},
new Author
{
AuthorId = 2,
Name = "Scott",
Book = new Book {BookId = 2, Name = "MVC4", IsPublished = true}
}
};
}
}
Now create a method and test all of these queries an see the result:
var query = from a in authors
orderby a.AuthorId
from b in books
orderby b.BookId
select new { a, b };
Note: selects from authors and sets by Id, select from books and order by Id and finally returns the selected Items from author and Book!
var query2 = from a in authors
join b in books on a.AuthorId equals b.BookId
select a;
var query3 = from a in authors
where a.Book.Name == "MVC4"
select new { x = a.Book, a };
var query4 = from b in books
join a in authors on b.BookId equals a.AuthorId
where b.Name == "Eric"
select b;
var query5 =
from b in books
where b.Name == "DDD"
select new {b.Name, b.IsPublished}
into x
orderby x.Name
select x;
var query6 =
from b in books
select new {b.Name, b.BookId}
into x
orderby x.Name
select x;
var query7 =
from b in books
orderby b.PulishDate descending
select b;
example three
Create two class named Product and Category with these definitions:
public class Category
{
public int CategoryId { get; set; }
public string CategoryName { get; set; }
}
public class Product
{
public int ProductId { get; set; }
public string ProductName { get; set; }
public Category Category { get; set; }
}
And then add a Data Generator class to Generate some Fake Date to work with!
public class ListGenerator
{
private List<Category> _categories;
private List<Product> _productList;
private void CategoryList()
{
_categories = new List<Category>()
{
new Category
{
CategoryId = 1,
CategoryName = "Yammi"
}
};
}
private void ProductList()
{
_productList = new List<Product>
{
new Product
{
Category = _categories.Single(c => c.CategoryName == "Yammi"),
ProductId = 1,
ProductName = "cholocalte"
}
};
}
}
Now Create a method to write some different queries :
var query =
from cat in _categories
join pro in _productList on cat equals pro.Category into p
from s in p
select new {s.ProductName};
var query2 =
(from pro in _productList
where pro.ProductId == 2
select pro).First();
var query3 =
from pro in _productList
group pro by pro.Category
into proGroup
select new {productNumber = proGroup.Count()};
And finally for more information about LINQ refer to this address :
http://msdn.microsoft.com/en-us/library/bb425822.aspx
