from clause

Learn to start query syntax with from.

The from clause

Query syntax is a SQL-like way to write LINQ queries. Every query starts with from. It declares a range variable and the data source: from n in numbers.

Here n represents each element; numbers is the source. The range variable is in scope for the rest of the query, much like the iteration variable in foreach. Query syntax is preferred when method chains feel less readable.

The range variable

The range variable is a name in scope for the rest of the query. In from n in numbers, n is the range variable. You use it in the remaining clauses (where, select, orderby).

It is similar to the iteration variable in foreach, but the query is not executed yet — only defined. It runs when you loop over it with foreach or call ToList().

Exercise Write your first query syntax query

Write a query from n in numbers select n for the numbers array below. Iterate the result with foreach and print each element with Console.WriteLine(n).

Show example solution

Start the query with from n in numbers, end with select n;. Then loop with foreach (var n in query) { Console.WriteLine(n); }.
Example solution:
using System;
using System.Linq;

class Program
{
    static void Main()
    {
        int[] numbers = { 1, 2, 3, 4, 5 };
        var query = from n in numbers
                    select n;
        foreach (var n in query)
        {
            Console.WriteLine(n);
        }
    }
}

Test yourself

What does the from clause do?
- It ends the query
- It declares a range variable and specifies the source
- It applies a filter predicate
- It performs sorting
Show answer

It declares a range variable and specifies the source — Correct. from declares the range variable and the data source.

Complete the from clause

var query = ____ n in numbers select n;

Show answer

var query = from n in numbers select n;

Match each clause to its role

from

Starts the query
where

Filters
select

Projects
orderby

Sorts

Next lesson: where in query

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