Combining relational and NoSQL databases in a Rails app.

1. Mixin' it Up:
Datastore
Edition
Chris Cahoon
Eric Oestrich

3. Using only an
object store
on a largeish app
and then remembering you can use more
than one database in a system

4. The (Central) Problem
Hierarchical forms & responses

5. Survey Response
Question (text) Answer
Question Group Answer Group
Question (date) Answer (date)
Question (phone #) Answer (phone #)

6. NUMBERS
Lots of questions
Lots of forms
Lots of users
Lots of responses
= Lots of queries

7. "We need an
object store!"

8. MONGOID!
feels like ActiveRecord inside MongoDB

10. "This form belongs_to
user!"

11. "Mongoid has helpers for
relations?!"

12. Response Survey
User
Not bad.

13. (months pass...)

15. User
Survey
Campaign
(etc.) (very etc.)
Organization
Response
Oh.

17. Mongoid works perfectly
for those two models

18. ...but everything
else is relational!

20. There are
problems with
object stores

21. ... used like a
relational db
(there are things we
missed from relational
DBs)

22. Relations

23. Can only query
one collection at
a time

24. Denormalization

25. No foreign keys

26. I accidentally the object

27. Can I have my cake?
and eat it too?

29. Just Mongoid

30. Querying
# 2 queries
surveys = Survey.where(:campaign_id.in =>
@user.campaigns.map(&:id))
survey_ids = surveys.map(&:id)
# + 1 query
Response.where(:survey_id.in => survey_ids,
:complete => true).first.answers
# = 3 total queries for search, not
chainable

31. Interlude

33. Mongoid & ActiveRecord

34. Bridging the gap

36. Search with SQL, store
with Mongo
# 1 query
Response.
joins(:survey, :campaign).
where('complete' => true,
"campaigns.user_id" => @user.id). first.
answer_collection
# = 1 total query for search, chainable

39. Should we gemify this?

40. GitHub:
https://github.com/oestrich/mixin_it_up_datastore
(look at the branches)

41. Thanks