after_create callback and update trigger syntax

rubyonrails-talk
1

Hi people

I have a doubt.

I have 2 tables (models) "Product" and "Purchase". I want to use the callback after_create to update the attribute Product.quantity every time a Purchase is created, so I think this should be work, but I don't know the right syntax

In purchase model

def after_create          Product.update(product.quantity = product.quantity + purchase.quantity) end

can somebody help me with this?? thanks

2

do you have some relation here?

eg

product   has_many :purchases

puchase (has column product_id)   belongs_to :product

and in purchase.rb   after_create :increase_product_purchase

def increase_product_purchase   product.increase_purchase end

and in product.rb

def increase_purchase   update_attribute(:number_of_purchases, number_of_purchases + 1) end

3

no, that's not what I'm looking for

product.quantity is the current amount of products purchase.quantity is the amount of products I buy

so the new product.quantity should be the "old" product.quantity + purchase.quantity

eg

current product.quantity = 5 purchase.quantity = 20

new product.quantity = 25

4

God,

def increase_product_purchase   product.increase_quantity(quantity) end

in product def increase_quantity(quantity)   update_attribute(:quantity, number_of_purchases + quantity) end

or simply in purchase

def increase_product_purchase   product.update_attribute(:quantity, product.quantity + quantity) end

?

5

Thanks for your help

The last option worked for me

def increase_product_purchase   product.update_attribute(:quantity, product.quantity + quantity) end

it was pretty simple, but I couldn't figured out...

Thanks again