Here's a gist with a clearer example of the problem I discuss below.
http://gist.github.com/186348
I'm currently using dm 0.9.11 with mysql.
Say I have users and books, and those books can be public or private.
I then have a 'readers' table which maps what books people can read.
I then want to return a list of books for a user which are *either*
public or has the user as an allowed reader, eg:
class User
end
class Reader
belongs_to :user
belongs_to :book
end
class Book
property :private, Boolean, :default => true
has n, :readers
def self.accessible_by(user)
all(
:links => [Book.relationships[:readers]],
:conditions => ["(readers.user_id = ? OR books.private = ?)",
user.id, false]
)
end
end
>> Book.accessible_by(current_user)
This works fine for private books, but for ones which are public it
will return duplicate records due to joining on the readers table
(assuming the public book has a number of readers)
In mysql I could use distinct, eg something like:
SELECT DISTINCT books.*
FROM books
INNER JOIN readers ON readers.book_id = books.id
WHERE readers.user_id = 10 OR books.private = FALSE
But I can't see a way of doing that easily with datamapper.
Obviously I could turn this example into a manual query, but that
isn't possible (that I'm aware of) in the actual use-case because I'm
using this as part of larger queries/chains for example:
>> current_account.books.accessible_by(current_user).all(:name.like => "%foo%",
>> :order => [:created_at.asc])
Is there a way of achieving this with datamapper, or does anyone have
any recommendations of how I could change the architecture to make
this easier?
Thanks in advance for any help.
--
Richard Livsey
Minutebase - Online Meeting Minutes
http://minutebase.com
http://livsey.org
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