How to use foreign keys in Ruby on the Rails query?

Question

I have three models; events, users and entries. I would like on my users page for to be able to retrieve information relating to the events associated with the event associated with the user.

def show
    @user = User.find(params[:id])
    @entry = @user.entries.paginate(page: params[:page])
  end

It is more than happy with @user.entries.count but I would like to link up in a table something like this:

Event Name - Event Location - Course

My models are bellow:

class Event < ApplicationRecord
    has_many :entries, dependent: :destroy

class User < ApplicationRecord
    has_many :entries, dependent: :destroy

class Entry < ApplicationRecord
    belongs_to :user
    belongs_to :event

Sebastián Palma · Accepted Answer · 2017-12-04 20:51:33Z

1

If they're related as:

class User < ApplicationRecord
  has_many :events
end

class Event < ApplicationRecord
  has_many :entries
  belongs_to :user
end

class Entry < ApplicationRecord
  belongs_to :event
end

Then you can use joins starting from Entry, up to User and check events where the user id is the one what you need:

Entry.joins(event: :user).where(users: { id: user_id })

answered Dec 4, 2017 at 20:51

Sebastián Palma

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9 Comments

Tom Snow Over a year ago

I get this error on rails console. 'NameError: undefined local variable or method user_id for main:Object' ?

Sebastián Palma Over a year ago

user_id is a placeholder value I added as example, you need to use a numeric value corresponding to any user id that you know exists in your database @Tom :).

Tom Snow Over a year ago

I tried - entry = Entry.joins(event: :user).where(users: { id: 2 }) I still get nowhere. Apparently, 'ActiveRecord::ConfigurationError: Can't join 'Event' to association named 'user'; perhaps you misspelled it?' . What should 'user' refer to?

Sebastián Palma Over a year ago

Okay, I'm looking at your models now.

Sebastián Palma Over a year ago

For your models, does this work Entry.joins(:event, :user).where(users: { id: 1 })?

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