How to get last N records with activerecord?

Question

With :limit in query, I will get first N records. What is the easiest way to get last N records?

Answer 1

An active record query like this I think would get you what you want ('Something' is the model name):

Something.find(:all, :order => "id desc", :limit => 5).reverse

edit: As noted in the comments, another way:

result = Something.find(:all, :order => "id desc", :limit => 5)

while !result.empty?
        puts result.pop
end

Answer 2

This is the Rails 3 way

SomeModel.last(5) # last 5 records in ascending order

SomeModel.last(5).reverse # last 5 records in descending order

Answer 3

new way to do it in rails 3.1 is SomeModel.limit(5).order('id desc')

Answer 4

For Rails 4 and above version:

You can try something like this If you want first oldest entry

YourModel.order(id: :asc).limit(5).each do |d|

---

You can try something like this if you want last latest entries..

YourModel.order(id: :desc).limit(5).each do |d|

Answer 5

Solution is here:

SomeModel.last(5).reverse

Since rails is lazy, it will eventually hit the database with SQL like: "SELECT table.* FROM table ORDER BY table.id DESC LIMIT 5".

Answer 6

For Rails 5 (and likely Rails 4)

Bad:

Something.last(5)

because:

Something.last(5).class
=> Array

so:

Something.last(50000).count

will likely blow up your memory or take forever.

Good approach:

Something.limit(5).order('id desc')

because:

Something.limit(5).order('id desc').class
=> Image::ActiveRecord_Relation

Something.limit(5).order('id desc').to_sql
=> "SELECT  \"somethings\".* FROM \"somethings\" ORDER BY id desc LIMIT 5"

The latter is an unevaluated scope. You can chain it, or convert it to an array via .to_a. So:

Something.limit(50000).order('id desc').count

... takes a second.

Answer 7

If you need to set some ordering on results then use:

Model.order('name desc').limit(n) # n= number

if you do not need any ordering, and just need records saved in the table then use:

Model.last(n) # n= any number

Answer 8

In my rails (rails 4.2) project, I use

Model.last(10) # get the last 10 record order by id

and it works.

Answer 9

I find that this query is better/faster for using the "pluck" method, which I love:

Challenge.limit(5).order('id desc')

This gives an ActiveRecord as the output; so you can use .pluck on it like this:

Challenge.limit(5).order('id desc').pluck(:id)

which quickly gives the ids as an array while using optimal SQL code.

Answer 10

Just try:

Model.all.order("id asc").limit(5)

Answer 11

If you have a default scope in your model that specifies an ascending order in Rails 3 you'll need to use reorder rather than order as specified by Arthur Neves above:

Something.limit(5).reorder('id desc')

or

Something.reorder('id desc').limit(5)

Answer 12

Let's say N = 5 and your model is Message, you can do something like this:

Message.order(id: :asc).from(Message.all.order(id: :desc).limit(5), :messages)

Look at the sql:

SELECT "messages".* FROM (
  SELECT  "messages".* FROM "messages"  ORDER BY "messages"."created_at" DESC LIMIT 5
) messages  ORDER BY "messages"."created_at" ASC

The key is the subselect. First we need to define what are the last messages we want and then we have to order them in ascending order.

Answer 13

Add an :order parameter to the query