Rails changes postgres SELECT * to SELECT COUNT

Question

I am working with the RailsCast on token input and am trying to cleanup a query method for Postgres. I found this post for making my query DB-agnostic.

My method:

  def self.tokens(query)
    t = Language.arel_table
    languages = Language.where(t[:name].matches("%#{query}%"))
    if languages.empty?
      [{id: "<<<#{query}>>>", name: "New: \"#{query}\""}]
    end
  end

Returns

:001 > Language.tokens('Ru')
   (0.8ms)  SELECT COUNT(*) FROM "languages"  WHERE ("languages"."name" ILIKE '%Ru%')

But if I use return instead of language =, I get the correct query:

  def self.tokens(query)
    t = .arel_table
    return Language.where(t[:name].matches("%#{query}%"))
  end

:001 > Language.tokens('Ru')
  Language Load (0.9ms)  SELECT "languages".* FROM "languages"  WHERE ("languages"."name" ILIKE '%Ru%')

It's probably something obvious, but I cannot figure out why the first method is selecting count instead of all of the rows in the `languages' table db. I would really like to store the result of that query in a variable.

Brad Werth · Accepted Answer · 2014-07-27 00:38:46Z

1

It's because the where is resolved as lazily as it possibly can be (not until it is absolutely needed). In your case it needs it when you:

Explicitly return
Check empty?

The reason it is doing the count, is to determine via the count whether it is empty.

answered Jul 27, 2014 at 0:38

Brad Werth

17.7k10 gold badges67 silver badges89 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Rails changes postgres SELECT * to SELECT COUNT

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related