Rails SQL query builder... Or ActiveRecord query builder

Question

I need to run sql query like

sql = 'SELECT * FROM users WHERE id != ' + self.id.to_s + ' AND id NOT IN (SELECT artner_id FROM encounters WHERE user_id = ' + self.id.to_s + ')'
sql += ' AND id NOT IN (SELECT user_id FROM encounters WHERE partner_id = ' + self.id.to_s + ' AND predisposition = ' + Encounter::Negative.to_s + ')'
sql += ' AND cfg_sex = ' + self.sex.to_s + ' AND cfg_country = ' + self.country.to_s + ' AND cfg_city = ' + self.city.to_s
sql += ' ORDER BY rand() LIMIT 1'

It can be executed by AR.find_by_sql, but the code before is bad readable. Are there any query builder, which can build that query?

For example, Kohana (it is PHP framework, I am php developer, but I want to change that kid-language to ruby/rails) have a query builder, which works like this:

$sql = DB::select('*')->from('users');
$sql->where('id', 'NOT_IN', DB::expr('SELECT partner_id FROM encounters WHERE user_id = '.$user->id));
$sql->where('id', 'NOT_IN', DB::expr('SELECT user_id FROM encounters WHERE partner_id = '.$user->id.' AND predisposition = '.Encounter::Negative));
....
etc
...

Query which was builded with query builder like a Kohana query builder is more readable and understandable.

Are there any gem to solve this problem?

Answer 1

You need the squeel gem. It extends AR with blocks and makes very complicated queries with ease.

Just few features:

# not_in == cool! )
Product.where{id.not_in LineItem.select{product_id}}
# SELECT "products".* FROM "products" WHERE "products"."id" NOT IN 
# (SELECT "line_items"."product_id" FROM "line_items" )

# outer joins on pure Ruby:
LineItem.joins{product.outer}
# LineItem Load (0.0ms)  SELECT "line_items".* FROM "line_items" 
# LEFT OUTER JOIN "products" ON "products"."id" = "line_items"."product_id"

# calcs, aliasing:
Product.select{[avg(price).as(middle)]}
# SELECT avg("products"."price") AS middle FROM "products"

# comparison
Product.where{id != 100500}
Product.where{price<10}

# logical OR
Product.where{(price<10) | (title.like '%rails%')}
# SELECT "products".* FROM "products" WHERE (("products"."price" < 10 OR
# "products"."title" LIKE '%rails%'))

# xxx_any feature (also available xxx_all)
Product.where{title.like_any %w[%ruby% %rails%]}
# SELECT "products".* FROM "products" WHERE (("products"."title" LIKE '%ruby%' OR 
# "products"."title" LIKE '%rails%'))    

Note the using blocks: {...} here aren't hashes. Also note the absence of symbols.

If you decide to pick it, read the section that starts with "This carries with it an important implication"

Answer 2

There's a ruby library that utilizes relational algebra. It is called ARel. If you are using Rails 3.x, then you already have.

ids   = Partner.where(user_id: self.id).pluck(:partner_id) << self.id
users = User.where("id NOT IN #{ ids.join(',') }")