ruby - Simple Rails array not saving to array column -

i'm working rails 4.1.0, ruby 2.1.0, , postgres 9.3.0.0.

i'm trying save changes column array of hstores (an array of hashes in ruby parlance).

here's (simplified) code in product model, used saving changes:

def add_to_cart_with_credits(cart)     cart.added_product_hashes << {"id" => self.id.to_s, "method" => "credits"}     # reason, isn't saving (without exclamation, well)     cart.save! end 

a few things of note:

1. the cart initialised empty array in added_product_hashes column
2. i'm storing added products hashes because there couple of ways add products cart, , each require own logic remove , customise.
3. each user has own cart, , needs reference later, why carts saved db (instead of using session variable, guess).

any ideas i'm doing wrong? i'm not seeing error: server logs note cart.added_product_hashes column updates correctly, changes don't persist.

solution

as james pointed out, << doesn't flag record being dirty, edits array in-place. while wasn't changing hstores within array column, appears changes enclosing array aren't picked unless attribute explicitly reconstructed. below code fixes problem:

def add_to_cart_with_credits(cart)     cart.added_product_hashes = cart.added_product_hashes + [{"id" => self.id.to_s, "method" => "credits"}]     # we're go!     cart.save! end 

james suggests particular method more terse.

see "new data not persisting rails array column on postgres"

activerecord isn't recognizing change array attributes being updated in place.

you can this:

cart.added_product_hashes_will_change!