Rails scope works different in spec and console

Question

I have this class

class Invoice < ActiveRecord::Base
    scope :last_with_number, -> (firm) {firm.invoices.where('number IS NOT NULL').order("number ASC").last}
end

When I run Invoice.last_with_number(Firm.first).number in the console, I get this error

2.0.0p247 :001 > Invoice.last_with_number(Firm.first).number
  Firm Load (1.5ms)  SELECT "firms".* FROM "firms" ORDER BY "firms"."id" ASC LIMIT 1
  Invoice Load (3.1ms)  SELECT "invoices".* FROM "invoices" WHERE "invoices"."firm_id" = $1 AND (number IS NOT NULL) ORDER BY number DESC LIMIT 1  [["firm_id", 1]]
NoMethodError:   Invoice Load (0.7ms)  SELECT "invoices".* FROM "invoices"
undefined method `number' for #<ActiveRecord::Relation::ActiveRecord_Relation_Invoice:0x00000008793198>

But this spec passes

 describe Invoice do
    let(:firm)     {FactoryGirl.create(:firm)}
    let(:invoice1)   {FactoryGirl.create(:invoice, customer:customer, firm:firm , number: 2)}
    let(:invoice2)   {FactoryGirl.create(:invoice, customer:customer, firm:firm , number:3)}

    it 'gets the last numberd invoice for spesific firm' do 
        invoice1
        invoice2
        Invoice.last_with_number(firm).number.should eq 3
    end
 end

I can solve this problem by making a Invoice class method like this

def self.the_really_last(firm)
   last_with_number(firm).last
end

And change the scope from

scope :last_with_number, -> (firm) {firm.invoices.where('number IS NOT NULL').order("number ASC").last}

to

scope :last_with_number, -> (firm) {firm.invoices.where('number IS NOT NULL').order("number ASC")}

This will work both places.

But, why is the scope behaving differently in the the spec and the console?

Is it possible you have other typos that could explain this? In any event, the console is showing the correct behavior. I would do a `puts Invoice.last_with_number(firm)` inside your spec to see what kind of object you're getting and why the `number` method is present. If it's not a `Relation`, then I would double check your scope definition. — Peter Alfvin, Feb 27 '14 at 17:37
To isolate a bit: when I run the specs with `.last` at the end of the scope it passes. If I remove last and run specs I get `undefined method 'number' for #`. The issue here is that a scope should return a ActiveRecord::Relation. But, it does not when I run the the spec. Why? — Andreas Lyngstad, Feb 27 '14 at 21:08
Sorry, I didn't scroll your scope definition and missed the `.last` on the end. So, the mystery is not why your spec works, the mystery is why the console fails. I noticed there is an extra SQL query of `select * from invoices` logged to your terminal. If you don't add the `.last` from the console with your original scope definition (which includes the `.last) what does it return? — Peter Alfvin, Feb 27 '14 at 22:21
To put `.last` in a scope is actually not what its intended for. A scope should return a `ActiveRecord::Relation` not a instance. The behavior in the console is thus correct. It's the spec that's make's it behave funny. — Andreas Lyngstad, Feb 27 '14 at 22:38
That may be true, but defining a scope is the same as defining a class method, as stated explicitly in http://guides.rubyonrails.org/active_record_querying.html#scopes, so the `.last` _is_ getting called and that scope should return an instance of `Invoice`. Again, I suggest you execute just `Invoice.last_with_number(Firm.first)` from the console and see what it returns. — Peter Alfvin, Feb 27 '14 at 23:09
let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/48661/discussion-between-andreas-lyngstad-and-peter-alfvin) — Andreas Lyngstad, Feb 28 '14 at 09:31

score 0 · Accepted Answer · answered Mar 04 '14 at 10:24

I found out what it does. It happends when all records have number = nil. If you put last at the end of the scope it returns a ActiveRecord::Relation with all records. I made this repo to illustrate

This rails issue gets a good explanation

To avoid confusion never use last first or all in scopes

Rails scope works different in spec and console

1 Answers1