LINQ-Cheat-Sheet-Extension-Methods

LINQ Cheat Sheet By: Monir Hossain

Restriction
context.Courses.Where(c	=>	c.Level	==	1);	
Ordering
context.Courses	
							.OrderBy(c	=>	c.Name)		//	or	OrderByDescending
							.ThenBy(c	=>	c.Level);	//	or	ThenByDescending

Projection
context.Courses.Select(c	=>	new		
							{		
												CourseName	=	c.Name,	
												AuthorName	=	c.Author.Name		//	no	join	required
							});	
              
//	flattens	hierarchical	lists	
var	tags	=	context.Courses.SelectMany(c	=>	c.Tags);	

Grouping
var	groups	=	context.Courses.GroupBy(c	=>	c.Level);	


Inner Join
Use when there is no relationship between your entities and you need to link them based on a
key.
var	authors	=	context.Authors.Join(context.Courses,	
					a	=>	a.Id,		//	key	on	the	left	side	
					c	=>	c.AuthorId,			//	key	on	the	right	side,
					(author,	course)	=>			//	what	to	do	once	matched
								new	
								{
												AuthorName	=	author.Name,
												CourseName	=	course.Name
								}
);	


Group Join
Useful when you need to group objects by a property and count the number of objects in each
group. In SQL we do this with LEFT JOIN, COUNT(*) and GROUP BY. In LINQ, we use group
join.
var	authors	=	context.Authors.GroupJoin(context.Courses,	
					a	=>	a.Id,		//	key	on	the	left	side	
					c	=>	c.AuthorId,			//	key	on	the	right	side,
					(author,	courses)	=>			//	what	to	do	once	matched
								new	
								{
												AuthorName	=	author.Name,
												Courses	=	courses
								}
);	


Cross Join
To get full combinations of all objects on the left and the ones on the right.
var	combos	=	context.Authors.SelectMany(a	=>	context.Courses,	
				(author,	course)	=>	new	{
								AuthorName	=	author.Name,
								CourseName	=	course.Name	
				});	
								
                
Partitioning
To get records in a given page.
context.Courses.Skip(10).Take(10);	


Element Operators

//	throws	an	exception	if	no	elements	found		
context.Courses.First();	
context.Courses.First(c	=>	c.Level	==	1);	

//	returns	null	if	no	elements	found		
context.Courses.FirstOrDefault();		

//	not	supported	by	SQL	Server	
context.Courses.Last();	
context.Courses.LastOrDefault();
context.Courses.Single(c	=>	c.Id	==	1);
context.Courses.SingleOrDefault(c	=>	c.Id	==	1);


Quantifying
bool	allInLevel1	=	context.Courses.All(c	=>	c.Level	==	1);	
bool	anyInLevel1	=	context.Courses.Any(c	=>	c.Level	==	1);	

Aggregating
int	count	=	context.Courses.Count();	
int	count	=	context.Courses.Count(c	=>	c.Level	==	1);	
var	max	=	context.Courses.Max(c	=>	c.Price);	
var	min	=	context.Courses.Min(c	=>	c.Price);	
var	avg	=	context.Courses.Average(c	=>	c.Price);	
var	sum	=	context.Courses.Sum(c	=>	c.Price);