find_by_exceptions.md

Exceptions Raised by find_by vs. find

I previously believed that the following were the same - the former being the more concise, and by extension making the latter overly verbose:

ObjectModel.find(3) # good
ObjectModel.find_by(id: 3) # bad?

Today, one of my teammates (@dleve123) pushed up a PR with the latter line. One of the finer points of find_by is that attempting to retrieve an id that doesn't exist will simply return nil. I now understand that the following is more accurate:

ObjectModel.find(3) # good
ObjectModel.find_by!(id: 3) # bad!

ObjectModel.find_by(id: 3) # good, when trying to avoid exceptions

find_by! will raise an exception and makes the first two essentially the same. It should be noted that the dynamic find_by_[attribute] methods follow the same convention, though they are mildly deprecated. This also extends to all other uses of the find_by methods with attributes other than id:

ObjectModel.find_by!(name: "foo") # use when exceptions should be raised
ObjectModel.find_by(name: "foo")  # use when exceptions should be surpressed