How Could I use SQL IN command in Rails?

Question

def show_user_events
    user = current_user
    @join_events = JoinEvent.find_all_by_user_id(user.id)
    # @events = Event.where(:id => @join_events)

    respond_to do |format|
       format.html # show_user_events.html.erb
       format.json { render json: @events }
    end
end

I want to get the specific values in the 'Event'. The 'event_id' is one of the attributes of the 'JoinEvent'. Using the 'event_id' values of '@join_events', I want to get the same effect as the command in the SQL query.

SELECT * FROM events
WHERE id in (join_events[1].event_id, join_events[2].event_id, ...)

What should I do to achieve this effect in rails?

Community · Accepted Answer · 2020-06-20 09:12:55Z

1

There is at least two ways to do this implicitly or explicitly respectively:

JoinEvent.find([1, 2, 3]) # short for JoinEvent.where(id: [1, 2, 3])
JoinEvent.where(event_id: [1, 2, 3])

JoinEvent.where("event_id IN (?)", [1, 2, 3])

I prefer first approach when it's possible

Thus in your case you can collect ids by:

@join_events = JoinEvent.where(user_id: current_user.id)
@join_events_ids = @join_events.pluck(:id)

or (more prefered way)

current_user.join_event_ids

Comes with has_many association

collection_singular_ids

Returns an array of the associated objects’ ids

edited Jun 20, 2020 at 9:12

CommunityBot

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answered May 11, 2013 at 6:36

ck3g

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2 Comments

kiddorails Over a year ago

If I recall correctly, pluck works on Relation; not on Array. find_all_by_user_id will give you an array and pluck won't work on that.

Sung-Jun Kim Over a year ago

Thank you for your answers :) It has been a great help to me.

kiddorails · Accepted Answer · 2013-05-11 06:38:35Z

0

JoinEvent.where(:event_id => [@join_events.map(&:id)])

answered May 11, 2013 at 6:38

kiddorails

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2 Comments

ck3g Over a year ago

With these extra [] you will get [[1, 2]]. Thus you don't need them

Sung-Jun Kim Over a year ago

Thank you for your answers :) It has been a great help to me.

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