Get all associated data for all records of a model type in Rails? -

how meld getting of associated data of records of given model?

i have following models:

user --n:1--> reservation <--1:n-- concert 

so pseudo-code:

reservation belongs_to user reservation belongs_to concert user has_many reservations user has_many concerts through reservations concert has_many reservations concert has_many users through reservations 

how make single big array of everything?

• i can reservations via reservation.all
• i can user particular reservation via reservation.find(25).user
• i can concert particular reservation via reservation.find(25).concert

but how of them? if do

reservation.all.each |res|    res.user.name+","+res.concert.name+","+res.concert.date # etc. end 

then 2 new database queries each reservation loops through. 10 records, might not matter, thousands, can painful. add other associations (e.g. concert belongs_to venue, user has_one email, etc.)...

is there way say, "get of reservations , following attached info" loads in single sql query?

what you're trying accomplish called eager loading, , can done using includes in activerecord. see below:

n + 1 queries problem

active record lets specify in advance associations going loaded. possible specifying includes method of model.find call. includes, active record ensures of specified associations loaded using minimum possible number of queries.

http://guides.rubyonrails.org/active_record_querying.html#eager-loading-associations

in example use following:

reservation.all.includes(:user, :concert) 

---

it idea specify :inverse_of option :belongs_to relations. optimizes object loading , makes sure cross-referencing model point same object in memory, i.e.:

@user == @user.reservations.first.user # true 

more information available here:

if using belongs_to on join model, idea set :inverse_of option on belongs_to ...

http://api.rubyonrails.org/classes/activerecord/associations/classmethods.html

in example:

# app/models/reservation.rb  belongs_to :user, :inverse_of => :reservations belongs_to :concert, :inverse_of => :reservations