Before the form attempted to read an email value from the Instructeur
model, and failed (because the empty Instructeur had no user yet).
We could let `Instructeur#email` return `nil` if there is no User –
but as a created Instructeur is always supposed to have a User, this
seems like a nice safeguard to keep.
So instead this commit rewrites the create form, which now doesn’t
depend on an Instructeur model. Seems easy enough for now.
It kind of worked until now, because the email field is disabled, and
thus never accessed.
But better make it clean, by accessing an object (User) where the email
field actually exists.
The `joins` are declared explicitely in order to associate a predictable
name to the joined table.
Otherwise, when the query is joined with `:users`, ActiveRecord will
alias the join automatically to solve the conflict. Unfortunately, the
automatic resolution means that the table name becomes unpredictable,
and thus unsuitable to perform queries on.
Now that `Instructeur.email` is merely an alias to `instructeur.user.email`,
and we changed every occurence of `instructeurs.pluck(:email)` to
`instructeurs.map(&:email)`, the new version using `map` may cause N+1 queries
if the users have not been preloaded.
It makes sense to always preload the user when fetching an Instructeur:
- Instructeur and User have a strongly coupled relationship
- It avoids N+1 queries everywhere in the app
Of course fetching an instructeur without needing its user will now do an
unecessary fetch of the associated user. But it seems better than leaving
a risk of N+1 queries in many places.
Make it more reusable, by:
- Renaming `attachment/update` to `attachment/edit`
- Refactoring the CSS styles into their own stylesheet
- Allow to specify the 'accept' option
- Remove the unused `.radios.vertical`
- Add a `.editable-champ-radio.vertical` variant for vertical radios
- Add an example of vertical radios to the patron
- Use vertical radios to display the procedure options
