On Saturday, December 2, 2017 at 11:10:06 PM UTC-5, Andrew Burleson wrote:
>
> 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
>
>
>
I'm presuming you meant that Book would have review statuses, so you would
define a dataset method on Book.
class Book < Sequel::Model
dataset_module do
subset :pending_review, review_status: "pending_review"
end
end
which you would then use as a condition in your many_to_many:
class Group < Sequel::Model
one_to_many :book_groups
many_to_many :books, join_table: :book_groups
many_to_many :books_pending_review, join_table: :book_groups, class:
:Book, right_key: :book_id do |ds|
ds.pending_review
end
end
Unless you meant that books being submitted to groups would be reviewed
individually for each submission? Your join table sounds like it doesn't
have the review status, but if it does, that changes a bunch of things.
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