Postgres returns the last item on the array instead the first

Question

I have on my controller something like

@account = @user.accounts.first

where I only want to display the first item in the accounts array. But whenever I add a new account, @account now refers to the last item in the accounts array.

Locally, with SQLite3, it works correctly, @account always refers to the first item in the accounts array, but on heroku with postgresql, is when that happens.

Why this is happening?

score 1 · Accepted Answer · answered Dec 20 '13 at 13:17

1

According to this issue in the rails repository, you should explicitly state the ordering to ensure this works correctly:

@account = @user.accounts.order(:created_at).first

answered Dec 20 '13 at 13:17

benjaminjosephw

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Nice hat..you got.. :) – Arup Rakshit Dec 20 '13 at 13:19
1

Also this info on Postgres ordering may be helpful http://stackoverflow.com/a/13191075/2463468 – benjaminjosephw Dec 20 '13 at 13:19
1

I eventually found a similar issue here on SO http://stackoverflow.com/questions/6525858/increment-counter-and-rails-first-using-postgresql-strange-behavior – tvieira Dec 20 '13 at 13:23

score 0 · Answer 2 · answered Dec 20 '13 at 13:18

Postgres tables do not have an implicit order. If you want a guaranteed order, you need to add .order to your query:

@account = @user.accounts.order(id: :asc).first

would give you the first account created for this user,

@account = @user.accounts.order(id: :desc).first

the last.

Postgres returns the last item on the array instead the first

2 Answers2