Finding User Objects

Active Record provides several options for finding objects. Let’s use them to find the first user we created while verifying that the third user (foo) has been destroyed. We’ll
start with the existing user:

Here we’ve passed the id of the user to User.find; Active Record returns the user with that id. 

               Let’s see if the user with an id of 3 still exists in the database:

  Since we destroyed our third user in Section 6.1.3, Active Record can’t find it in the database. Instead, find raises an exception, which is a way of indicating an exceptional event in the execution of a program—in this case, a nonexistent Active Record id, which causes find to raise an ActiveRecord::RecordNotFound exception.8 In addition to the

                generic find, Active Record also allows us to find users by specific attributes:

The find_by_email method is automatically created by Active Record based on the email attribute in the users table. (As you might guess, Active Record creates a find_by_name method as well.) Since we will be using email addresses as usernames, this sort of find will be useful when we learn how to let users sign in to our site (Chapter 7). If you’re worried that find_by_email will be inefficient if there are a large number of users, you’re ahead of the game; we’ll cover this issue, and its solution via database indices, in Section 6.2.5. 

            We’ll end with a couple of more general ways of finding users. First, there’s first:

Naturally, first just returns the first user in the database. There’s also all: 

No prizes for inferring that all returns an array (Section 4.3.1) of all users in the database.