Mysql join in rails - mysql

Question

I have two tables orientations and registrations that I would like to perform a join query on. Here is the schema for each of the tables...
create_table "orientations", :force => true do |t|
t.date "class_date"
t.text "class_time"
t.integer "seats"
t.boolean "active", :default => true
t.datetime "created_at", :null => false
t.datetime "updated_at", :null => false
end
create_table "registrations", :force => true do |t|
t.integer "orientation_id"
t.string "first_name"
t.string "last_name"
t.string "email"
t.string "student_id"
t.string "phone"
t.string "registration_cancellation_token"
t.datetime "registration_cancelled_at"
t.boolean "checked_in", :default => false
t.boolean "cancelled", :default => false
t.datetime "created_at", :null => false
t.datetime "updated_at", :null => false
t.text "program"
end
What I am looking for is all registrations for all orientations between two dates. I came up with this...
Registration.where(Orientation.where created_at: => #start_date..#end_date)
Of course that syntax is bogus, but hopfully it will help get across what I am looking for.

Answer 1

Use this to get all registrations for all orientations between two dates:
Registration.joins(:orientation).where(orientations: {:class_date => #start_date..#end_date})
joins performs an INNER JOIN which filters the rows that don't have association.
But, if you wish to keep the rows that don't have associations then go for includes which performs a LEFT OUTER JOIN
Registration.includes(:orientation).where(orientations: {:class_date => #start_date..#end_date})