I have an app where there are Writing Groups:
- Each group can have many Users.
- Users can have many books.
- Users can submit a book to a group.
- Books then proceed through several states, such as "pending review" ->
"in review" -> "accepted" | "rejected", etc.
The Group <-> Books relation is very simple to set up using a table
`group_books` with the primary key (group_id, book_id).
The basic associations are very easy to set up:
class Group < Sequel::Model
one_to_many :group_books
many_to_many :books, join_table: :group_books
end
<3 Sequel!
Now, using the group it would be helpful to filter books based on what
state they're in, eg. rather than show me all books, show me all books that
are pending review. In the database this means the group book's
`review_status` column has the value `pending_review.`
It's possible to declare that association like so:
many_to_many :books_pending_review, join_table: :group_books, class: :Book,
right_key: :book_id do |ds|
ds.where(review_status: 'pending_review')
end
This works fine, but in practice I have some qualms with it:
First, it duplicates knowledge. For instance, in the GroupBooks model I
would want to have the following:
dataset_module do
def pending_review
where(review_status: 'pending_review')
end
end
Now, I can chain that association if I want to return the group book
records, e.g.: `group.group_books.pending_review`, but that returns the
join models, not the book models.
I'd prefer that the enum values that define book states in the database be
limited to the GroupBook class and be referenced via methods from the
outside world.
A secondary, less important concern, is that this ends up being very
verbose if you have a large number of filtered associations in a full-size
app.
So, is there a cleaner or better way to do this, ideally defining the
filtered associations in one place (GroupBook) and simply referencing them
(or chaining them) elsewhere?
Thanks!
- Andrew
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