Activerecord query with array in where clause

Question

I have a location table in my rails app which has four columns :-

| Id | Longitude | Latitude | user_id

Now I have an array containing the list of user_ids. How can I write an active record query to select the last row of each user id. For example, if I have three user_ids in my array [1,2,3] I want the query to return just the last row corresponding to each user_id (lets assume entries for each user_id is present in the table) from the table.

So, far I am able to get all the rows corresponding to all the user_ids using this following query:

@ids = [1,2,3]
@locations = Location.where(user_id: ids)

How can I modify this activerecord query so that it returns only the last row corresponding to each user_id

Possible duplicate of ActiveRecord - select first record from each group — Kristján
– Kristján, Commented Dec 7, 2015 at 16:29

seancdavis · Accepted Answer · 2015-12-07 16:33:25Z

1

Assuming you have a User model that has many locations, you could start from the user model and use the association to get to your last location for each user.

User.where(:id => @ids).includes(:locations).collect { |u| u.locations.last }

User.where(:id => @ids) returns your collection of user objects.
includes(:locations) eager loads the associated locations, so we don't run into an n+1 problem.
collect { |u| u.locations.last } maps the last associated location into an array

answered Dec 7, 2015 at 16:33

seancdavis

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Sahil · Accepted Answer · 2015-12-07 17:04:19Z

0

You can also try this:

@ids = [1,2,3]
@locations = @ids.map {|id| [Location.where(user_id: id).last.location,User.find(id).name]}
#This would give you something like this: [["US",XYZ],["IND","ABC"]]

edited Dec 7, 2015 at 17:04

answered Dec 7, 2015 at 16:40

Sahil

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2 Comments

Lovish Choudhary Over a year ago

Doing a little bit of editing like @locations = @ids.map {|id| Location.where(user_id: id).last} makes this solution work. I want to ask one more thing, how can I add user name corresponding to the user_id (User has_many Locations relationship in the response ?

Sahil Over a year ago

Please check the updated answer, let me know if it's working

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