Ruby on Rails Active Record inner join not working

Question

I have 2 models: Engagement, user. Engagement basically refers to the items booked by the user. each engagement is for a specific user. user in engagement has a foreign key. I want to join engagement with user so that i can see the details of the user.

Here are my models

class Engagement < ActiveRecord::Base
  belongs_to :food_item  
  belongs_to :user
end
class User < ActiveRecord::Base
    has_many :engagements
    has_many :food_item, through: :engagements
end

I am running below query:

Engagement.joins("INNER JOIN users ON users.id = engagements.user_id")

It is not joining both the tables.

Any help will be appreciated

Just a comment, Rails uses inner join by default, so you could do Engagement.joins(:user) — Marcelo Risoli
– Marcelo Risoli, Commented Jan 20, 2016 at 15:47
He thanks for prompt replies, I not getting any error messages from the query but the issue is I am also not getting the users information. — Euler
– Euler, Commented Jan 21, 2016 at 4:53
@marcelo the query you mentioned is also fetching me the same result. Thanka fro suggestions anyway — Euler
– Euler, Commented Jan 21, 2016 at 4:53

Alex Buschle · Accepted Answer · 2016-01-21 00:37:45Z

3

Your query is right. You're doing a inner join and only returning engagements that have a relation to user.

To return the user data you should do something like this: Engagement.select('tasks.*, users.*').joins(:user). This way the object will have engagement and user attributes. But that is not the Rails way.

The "correct" way is:

engagements = Engagement.includes(:user)
engagements.first.user # this will return the user data

This way you're getting all engagements and preloading the user data, this way avoiding n + 1 queries (Eager-loading) ;)

answered Jan 21, 2016 at 0:37

Alex Buschle

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1 Comment

Arpan Mukherjee Over a year ago

The problem with includes way is it will do another query with an IN clause on the associated table. But take a scenario where we just want to fetch one row from the DB and want to get all associations via an inner join. If we do includes there, it will anyway do separate queries for each association. In that case, should we do the first way you described?

Giovani Barcelos · Accepted Answer · 2016-01-20 23:51:30Z

0

Try this Engagement.joins(:users)

It should work.

answered Jan 20, 2016 at 23:51

Giovani Barcelos

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1 Comment

Euler Over a year ago

@giovani above query is also not fetching the user data. It is giving me the same result which the query I mentioned in the question

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