LINQ stands for Language
INtegrated Queries in the context of sql programming. These are like SQL queries used to manipulate collection
of objects through entity framework. LINQ are queries that can be directly written in c# programming language and will be
translated to SQL statements and executed against the database. It simplify the complex process of database developer to query in databases.
These type of queries are executed on collection of
IEnumerable<T> or IQueryable<T> and as results are returned new
collection of IEnumerable<T> objects. In this post I will explain some example that show how to use
LINQ on collection of objects in c# programming.
Let’s suppose we have a c# class Student having two properties i.e. Name and Age and of course a primary key Id. Now to get all records of students from database we have to write:
var
students = from student in dc.Student
select student;
In above code it will extract all columns from Student table like Id, Name and Age also. If we want only name and Age column then:
var students = from student in dc.Student
select new
{
student.Name,
student.Age
};
It will show only Name and
Age columns of all the records.
It’s very simple to get some records having where condition like in sql programming. In below code if we want to get all records
having age = "25" then the following code should be written:
var students = from student in dc.Student
where student.Age == 25
select student;
Now at the last if you want to get records
having age = "25" and name = "Rahul" then following line of code has to be written:
var students = from student in dc.Student
where student.Age == 25 &&
student.Name == "Rahul"
select student;So according to above examples, LINQ is very simple language to be queried with databases. Here dc is used for data context that is created through entity framework 5.