LINQ

What is LINQ

Stands for: Language Integrated Query
Gives you the ability to query objects.
You can query:
- Objects in memory, eg collections (LINQ to Objects)
- Databases (LINQ to Entities)
- XML (LINQ to XML)
- ADO.NET Data Sets (LINQ to Data Sets) You can chain LINQ methods like with jQuery.

LINQ Extentions Methods (LINQ to objects)

var cheapBooks = books
    .Where(b => b.Price < 10)
    .OrderBy(b => b.Title)
    .Select(b => b.Title);

Average	var avg = books.Average(b => b.Price); Returns the average price.
Count	var count = books.Count();
First	.First(); Used to get the first object in a collection. .First(b => b.Title == "Book Name"); If you supply a predicate (filter), it will return the first object matching your predicate. (In this case the first book with Title 'Book Name')
FirstOrDefault	.FirstOrDefault(b => b.Title == "Book Name"); If no match is found this will return the default value (in this case null)
Last	.First(); Used to get the last object in a collection. .Last(b => b.Title == "Book Name"); If you supply a predicate (filter), it will return the last object matching your predicate. (In this case the last book with Title 'Book Name')
LastOrDefault	.LastOrDefault(b => b.Title == "Book Name"); If no match is found this will return the default value (in this case null)
Max	var priceHigh = books.Max(b => b.Price); Will return book with highest price.
Min	var priceMin = books.Min(b => b.Price); Will return book with lowest price.
OrderBy	books.OrderBy(b => b.Title) - Order books by Title
Single	Return only a single item in the list. .Single(b => b.Title == "ASP.NET MVC"); If there is no objects that matches this criteria, an exception error will occur.
SingleOrDefault	Return only a single item in the list, but if no matching condition then default will be returned. .SingleOrDefault(b => b.Title == "ASP.NET MVC");
Skip	Use for paging data. Used in conjunction with Take. .Skip(2) Skip 2 objects
Sum	var priceTotal = books.Sum(b => b.Price); Will return sum of prices for all books.
Take	Use for paging data. Used in conjunction with Skip. .Take(3); Take 3 objects
Where	books.Where(b => b.Price < 10) - Return all books with price lower than 10
Select	Use for projections or transformation. .Select(b => b.Title)

LINQ Query Operators

Always start with the 'from' and ends with the 'select'

var cheapBooks =
    from b in books
    where b.Price < 10
    orderby b.Title
    select b.Title;