First, lets talk through some setup data. We are working with two
models: Journal and User. And their respective
A User has_many Journals
A Journal belongs_to a User
Your models currently look like the following:
Assuming the above already exists, now we want to ensure a reference between
the two models with a user_id column on the Journal. At this point you could use
the following command to build that migration
Test driving this in a console should work with the above associations
Who is the creator of the Journal?
The previous setup works as you would expect, but what if you wanted to better describe
who created a Journal without changing the classname for User?
You might want a column named creator that stores the user who created the journal.
This would allow for more readable association language for future developers.
Rails has some built in support to achieve just this using some additional arguments
within the belongs_to method. Note: this requires no changes to the User model.
Our model now responds to the column name creator the same way it would to a
standard user reference.
One step further
You can improve on this approach by adding an index and foreign key to the
creator_id column in the migration. This ensures referential integrity as well as
speeding up any queries based on creator_id.
Now you have a custom named column, that is constrained based on a foreign key
, and indexed for faster querying. There are plenty of other tricks with
associations that can also be found on Rails Guides.