Select objects by index of array in Rails 3

Question

I'm trying to select a collection of objects using ActiveRecord by the index in the array.

I know I can select Item.first or Item.last or single or range. But I want to update an arbitrary group by the index of their position in the array.

collection = Item.all.to_a
collection[3,5,9,11]

Is this possible?

Thanks in advance...

-- edit --

Thanks to tokland's help, I was able to get it to work perfect.

In case anyone else wants to do something similar, here is what I did:

yesterday = Time.now - 1.day
i = Item.all
new_items = i.values_at(1,3,5,10,11,14,18)
new_items.each{ |e| e.update_attributes(:published_at => yesterday) }

tokland · Accepted Answer · 2011-10-25 19:52:22Z

8

If you mean indexes in an array (not IDs):

collection.values_at(3, 5, 9, 11)

answered Oct 25, 2011 at 19:52

tokland

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3 Comments

Adam Over a year ago

Thanks tokland, This does work! I'm trying to update attributes on a collection for testing. is this the best way to get at it?

Adam Over a year ago

Actually, I believe I can't update attributes on an array. I think I need to do an each. I'll keep working at it. Thanks again tokland!

Adam Over a year ago

Thanks tokland. I got it working, and provided the code in my edit above... (hopefully that was the right place to do so)

WarHog · Accepted Answer · 2011-10-25 19:54:51Z

1

If i properly understand, you need

Item.find([3,5,9,11])

This is how you can find a record given an id. But it method throws an exception if there would be some id that doesn't exist.

Item.find_all_by_id([3,5,9,11])

That will work even if some of the ids don't exist.

edited Oct 25, 2011 at 19:54

answered Oct 25, 2011 at 19:47

WarHog

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2 Comments

Adam Over a year ago

Thanks WarHog, but I'm trying to avoid using ID's as this is for a test db, and they will be constantly changing...

WarHog Over a year ago

Aha, got it, sorry for my misunderstanding.. Then @tokland approach should help you.

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