Rails checking if a record exists in database

Question

What is the most efficient of way of checking if a database will return a record before processing it. Example: Truck.where("id = ?", id).select('truck_no').first.truck_no

This may or may not return a truck if the truck exists. What is the most efficient way for me to ensure the page will not crash when processing this request. How would I handle this both in the view and the controller if lets say I was using a loop to go through each truck and print out its number.

If the record does not exist I would like to be able to print out a message instead saying no records found.

Answer 1

If you want to check for the existence of an object why not use exists?

if Truck.exists?(10)   # your truck exists in the database else   # the truck doesn't exist end 

The exists? method has the advantage that is not selecting the record from the database (meaning is faster than selecting the record). The query looks like:

SELECT 1 FROM trucks where trucks.id = 10 

You can find more examples in the Rails documentation for #exists?.