Question

In a Rails(3.2) app, I have a class method on a Model like this:

def import(level, max = 10)
  db = ActiveRecord::Base.connection
  result = db.execute("SELECT word FROM levels WHERE level == #{level} AND word NOT IN (SELECT entry FROM words) limit #{max};");

It just imports 10 new words(create 10 records) at a time that do not exist as Word record yet.

The schema looks something like this:

create_table "levels", :force => true do |t|
  t.string  "word"
  t.integer "level"
end

create_table "words", :force => true do |t|
  t.string  "entry"
  t.integer "level",      :default => 0
  t.text    "definition"
  t.string  "thesaurus",  :default => "none"
end

I’m an SQL noob. Messing with rails dbconsole(sqlite3, I’m using sqlite3 on a server as well), I somehow came up with the raw sql query above. I sort of know that I can do the same thing with Arel. How am I supposed to construct the query with ActiveRecord?

Answer 1

The following (untested) should work. It uses pluck in the subquery.

Level.where(:level => level).where("word NOT IN (?)", Word.pluck(:entry)).limit(max)