LINQ Part 3 - Writing a query

Part 3 - Writing a query 

The quires operate on simple in-memory collections. A user can use any of the following three ways to create a query

1. Query Syntax
2.  Method syntax
3. Combination of query and method syntax

Query Syntax

Query syntax is based on the query keywords which are used to write a query expression. I explained some of the query keywords on my previous post. This helps user to write SQL style commands.

From MSDN, query syntax is the recommended way to write quires. One reason for this is readability factor. Along with that using query syntax we can make use of let and handle complex join operations.

var employeeSalaryQuery = from employee in employees where employee.Salary > 10000

Please note as described in the earlier post, query type is IEnumerable and they do not get executed until they are iterated over a foreach loop.

Method Syntax

Some of the query expressions are wrapped under a method call, i.e as a dot operation. So, if you put a ‘.’ After a list variable, you can find these methods.

Some of these methods returns that return singleton numeric values, such as Sum, Max, Min, Average..etc. Please note these methods will be called last in any query expressions.

List<int> numbers = new List<int>() { 1, 2, 3, 4, 5 };

double average = numbers.Average();

If the methods have parameters, parameters are supplied as lambda expressions. 

var employeeSalaryQuery = employees.Where(e => e.Salary>10000);

Mixed Query

As the name suggest, it contains both query syntax and method syntax. To create mixed queries, enclose query syntax in parenthesis and then call the methods (dot operators).

int employeeCount = (from employee in employees where employee.Salary > 10000).Count();

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