Empty DataMapper::Collection returns everything on chaining. Bug?

[Michael Kebbekus]

class Membership
include DataMapper::Resource

property :id, Serial
property :project_id, Integer
property :user_id, Integer

belongs_to :user
belongs_to :project
end

>> Membership.all(:project_id => [])
=> []
>> Membership.all(:project_id => []).class
=> DataMapper::Collection
>> Membership.all(:project_id => []).user
=> [#<User @id=1 @created_at=Tue Apr 19 21:31:54 UTC 2011
@updated_at=Tue Apr 19 21:31:54 UTC 2011 @full_name="Andy Goodell"
@hashed_password=<not loaded> @salt="HQG8wpuoa5" @active=true
@primary_email_id=1 @provenance="signup" @legitimized_at=nil
@entry_credentials="google" @admin=<not loaded>
@calendar_synced_setting=false @google_calendar_id_setting=nil
@nag_setting=<not loaded> @last_nagged_setting=<not loaded>
@newsletter_setting=<not loaded> @messaging_level_setting=1
@settings_converted=false @picture_file_name=nil
@picture_content_type=<not loaded> @picture_file_size=<not loaded>
@picture_updated_at=nil @editable_picture_file_name=nil
@editable_picture_content_type=<not loaded>
@editable_picture_file_size=<not loaded>
@editable_picture_updated_at=nil>]

Isn't this supposed to be a more efficient way of saying
Membership.all(:project_id => []).map(&:user) which returns []?

As far as why I'm searching for :project_id => [], this is a
simplified version of the real code. We calculate the list of project
ids we're interested in, but some users of our site are not on any
projects.

[Piotr Solnica]

Hi Michael

On Apr 20, 1:11 am, Michael Kebbekus <makebbe...@gmail.com> wrote:
> Isn't this supposed to be a more efficient way of saying
> Membership.all(:project_id => []).map(&:user) which returns []?

Yes it is. I don't know how your relationships are set up exactly, but
the following example works for me:

class Project

include DataMapper::Resource

property :id, Serial

has n, :memberships
has n, :users, :through => :memberships
end

class Membership
include DataMapper::Resource

belongs_to :project, :key => true
belongs_to :user, :key => true
end

class User

include DataMapper::Resource

property :id, Serial

has n, :memberships
has n, :projects, :through => :memberships, :via => :project
end

DataMapper.finalize
DataMapper.auto_migrate!

project = Project.create
user = User.create

project.users << user
project.save

# you can grab users either via project:
Project.all(:id => [project.id]).users

# or membership
Membership.all(:project_id => [project.id]).user

Hope this helps

Cheers!

# solnic

[Michael Kebbekus]

Hey sonlic,

That looks about right as per our setup, but what happens when you do
Membership.all(:project_id => []).user with an empty array?

I'm suggesting that I've found a bug, because I get back the whole
user table even though Memberhip.all(:project_id => []) correctly
returns an empty Datamapper::Collection.

>> Membership.all(:project_id => [])
=> []
>> Membership.all(:project_id => []).class
=> DataMapper::Collection

>> Membership.all(:project_id => []).user #returns every User!?!?

[RipTheJacker]

This is the query that is done when you search on an empty array:

SELECT "id" FROM "users" WHERE "id" IN (SELECT "user_id" FROM
"memberships") ORDER BY "id"

That is incorrect, and a bug. You can get around this by using two
statements:

memberships = Membership.all(:project_ids => []) # => will return an
empty array, as expected
memberships.users # => will return [] or the users

It probably isn't ideal, but at least when you do
Membership.all(:project_ids => []) on an empty array, no query gets
run.

[Michael Kebbekus]

Thanks RipTheJacker.

That's definitely the bug I was getting at, and that workaround helps!