arel getting started

arel_getting_started.rb

# equivalent constructors of arel table
model = Arel::Table.new 'model_table_name'
model = Arel::Table.new :model_table_name
model = Model.arel_table

# prepare arel query
model_query =  model.project(model[Arel.star]).where(model[:id].lte(20))

# executing query and obtains an array of Model objects
model_list = Model.find_by_sql model_query

# executing query obtains an array of hashes
resultset = ActiveRecord::Base.connection.execute model_query


# references
http://blog.donwilson.net/2011/11/constructing-a-less-than-simple-query-with-rails-and-arel/
https://github.com/rails/arel