Return values are extremely important, and I was reminded of this after banging my head against the wall trying to pass the last test of a Sinatra app lab. I mistakenly took the .find and .find_by methods at face value and assumed that the difference between them was insignificant. However, I learned that these two methods can produce very different results.
Both methods are “finder” methods available through the ActiveRecord gem. As the name suggests, they are used to find specific records in your database and return them as objects.
.find and .find_by have some differences in the arguments they can accept. .find accepts a record id or multiple record ids in the form of a list or an array (i.e. (1, 2, 3) or ( [1, 2, 3] )). .find_by accepts one or more conditions as arguments in the form of (attribute_name: value). The attribute name should correspond with a column name in your database. Both methods can find a record by its id, and I wrongfully assumed that you should always use .find to accomplish this.
The key difference between these methods is their return values when they cannot find a record that matches the given argument. If no record is found, .find returns RecordNotFound, whereas .find_by returns nil. The difference in return values becomes crucial when using these finder methods in RESTful controller actions.
In my case, I was using the .find method in a controller action designed to update a record. More specifically, I was using it in an if statement, which relies on boolean return values. I didn’t want a user to be able to edit a post that he/she did not author. If the requested post did not have a :user_id that matched the current user’s id, the program would redirect to a different page instead of rendering the edit form for that post. My program was breaking instead of redirecting to the specified route when it could not find a post with the given :id and :user_id. RecordNotFound is not truthy or falsey. On the contrary, .find_by returns nil, which is a falsey value, so my program is now able to redirect a user to the specified route in the conditional statement.
Using the .find_by method in RESTful controller actions can give you more power over which view is rendered and prevent your program from breaking when a record is not found.