Arel Finders

The problem with ActiveRecord today is that there is no way to construct queries outside "attribute = value" or using "OR" operator. The solutions so far are not so easy to do, and usualy involves creating fragments of SQL in string form.

But we have Arel. So, this must be solved, right?

Unfortunately, no. Arel's API is quite dificult to use, and its API is quite inconsistent and changes over time, resulting in difficult code to mantain.

ActiveRecord::Finder

So, the solution was to create an object, an "adapter-kind" of object. ActiveRecord::Finder is a kind of object that contains all attributes from a table, and allows you to OR or AND queries.

finder = ActiveRecord::Finder.new(Arel::Table.new(:users))
query = finder.age > 10 | finder.name == "Foo"
query.arel.to_sql
#Returns: users.age > 10 OR users.name = 'Foo'

But it is kind of tedious to do this everytime you want to search for users, so you can use ActiveRecord::Base#restrict with a block to construct your queries.

ActiveRecord's Finders

Integrating with ActiveRecord, it is possible to use restrict to find records on a ActiveRecord object. The syntax is quite simple:

User.restrict { |f| f.age > 18 }
#or
User.restrict { age > 18 }

ANDs work on the same way, too:

User.restrict { age > 18 & age < 20 }

All finders, so far:

#WHERE NOT (users.age < 10)
User.restrict { !(age < 10) }

#Comparission
User.restrict { age == 20 }
User.restrict { age >= 20 }
User.restrict { age <= 20 }
User.restrict { age != 20 }
User.restrict { age > 20 }
User.restrict { age < 20 }

#IN
User.restrict { age.in?([10, 20, 30]) }

#LIKE
User.restrict { name =~ "Foo%" }
User.restrict { name !~ "Foo%" }

#AND, and OR
User.restrict { (name == "Foo") & (age < 20) }
User.restrict { (name == "Foo") | (age < 30) }
User.restrict do 
  ( (name == "Foo") & (age < 20) ) |
  ( (name == "Bar") | (age > 20) )
end

Plase note that because of operator precedence in Ruby, we must add a parenthesis over the comparission before using & or |.

Constructing Queries

To avoid "merging" ActiveRecord::Relation's, there is a specific syntax to construct a complex query on ActiveRecord::Finder.

def search(name_to_search, params = {})
  query = User.new_finder { name == name_to_search }
  query = query & User.new_finder { age > params[:age] } if params.include?(:age)
  query = query | User.new_finder { age <= 10 } if params[:include_all_childs]
  User.restrict(query)
end

Using "joins"

To be simple, the Finder simply has the attributes from the table that it was created. So, to be able to find a record using attributes from one of the joined tables, it is possible to use ActiveRecord::Base#merge