Question

I have these two pieces of code that each return a relation inside the Micropost model.

scope :including_replies, lambda { |user| where("microposts.in_reply_to = ?", user.id)}

def self.from_users_followed_by(user)
  followed_user_ids = user.followed_user_ids
  where("user_id IN (?) OR user_id = ?", followed_user_ids, user)
end

When I run r1 = Micropost.including_replies(user) I get a relation with two results with the following SQL:

SELECT `microposts`.* FROM `microposts` WHERE (microposts.in_reply_to = 102) ORDER BY 
microposts.created_at DESC

When I run r2 = Micropost.from_users_followed_by(user) I get a relation with one result with the following SQL:

SELECT `microposts`.* FROM `microposts` WHERE (user_id IN (NULL) OR user_id = 102) ORDER 
BY microposts.created_at DESC

Now when I merge the relations like so r3 = r1.merge(r2) I got zero results but was expecting three. The reason for this is that the SQL looks like this:

SELECT `microposts`.* FROM `microposts` WHERE (microposts.in_reply_to = 102) AND 
(user_id IN (NULL) OR user_id = 102) ORDER BY microposts.created_at DESC

Now what I need is (microposts.in_reply_to = 102) OR (user_id IN (NULL) OR user_id = 102)
I need an OR instead of an AND in the merged relation.

Is there a way to do this?

Answer 1

Not directly with Rails. Rails does not expose any way to merge ActiveRelation (scoped) objects with OR. The reason is that ActiveRelation may contain not only conditions (what is described in the WHERE clause), but also joins and other SQL clauses for which merging with OR is not well-defined.

You can do this either with Arel directly (which ActiveRelation is built on top of), or you can use Squeel, which exposes Arel functionality through a DSL (which may be more convenient). With Squeel, it is still relevant that ActiveRelations cannot be merged. However Squeel also provides Sifters, which represent conditions (without any other SQL clauses), which you can use. It would involve rewriting the scopes as sifters though.