Sometimes, the default settings in a framework and associated tools can lead to trouble. The boolean type in Rails is one such.

The boolean type specified in a database migration is represented differently in different database management systems.

Rails comes along and tries to do the right thing in each of these cases, but in almost all the above, we’re still left with the possibility of an undefined state, neither true nor false. In most cases, this can be accomodated with “truthiness” and “falsiness”, but not always, as in the cases where you think you can apply a meaning to nil and it whines at you.

In discussions various places, it seems there is no optimal solution that works in all cases, but a common practice is to set both a default value and disallow nulls in the field, like so:

add_column :widgets, :frangible, :boolean, default: false, null: false

Thus making it clear(er) that frangible on the Widget model will only be true or false, and if it isn’t explicitly set, will be false by default.

There are cases where tristate or multistate values are useful, but I feel these should be explicit, perhaps using an enum if that’s your choice.