Building an ActiveRecord relation without having it execute the query

Question

I am trying to build a query as follows:

rel = article.where(version: 'some_version')
             .joins(:categories)
             .merge(Category.where(:uuid => 'some_cat_uuid'))

articles = rel.where(published: true).limit(10)
# etc.

The problem is the first query seems to execute no matter what I do. Am I doing something wrong?

Answer 1

When you run commands in the console, it automatically adds something similar to .inspect at the end to display the results of the command. For instance (this is in my app that I'm working on right now):

irb(main):061:0> Job.where(id: 251000)
  Job Load (3.8ms)  SELECT "jobs".* FROM "jobs" WHERE "jobs"."deleted_at" IS NULL AND "jobs"."id" = 251000
=> [#<Job id: 251000, {...}>]

So, your first line of code is just fine and would not normally execute the query, but since you were running it in the console it executes immediately so that it can display the results for you.

One way to get around this is to add ; nil to the end of the command, that way the console won't attempt to display the results (it'll just display nil as the result of that line. IE:

irb(main):062:0> Job.where(id: 251000); nil
=> nil

Doing it this way you should be able to do what you were expecting (delay execution of the query until you actually need the results):

rel = article.where(version: 'some_version')
             .joins(:categories)
             .merge(Category.where(:uuid => 'some_cat_uuid')); nil

articles = rel.where(published: true).limit(10); nil

Then you can execute the query by using articles.all (in Rails 3) or articles.to_a (in Rails 4)

Of course if you then move this code to a rake task or model or something you can drop those ; nil bits because they look a little cluttered and would be useless at that point.

Another point of contention for the console might be that it'll see that .where() {NEWLINE} and execute the query at that point, I tend to put the dot on the previous line to remove any ambiguity of where my command is ending:

rel = article.where(version: 'some_version').
             joins(:categories).
             merge(Category.where(:uuid => 'some_cat_uuid')); nil