After_create callback and update trigger syntax

Rails
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

On Jul 20, 2011, at 23:08 , Angelo C. wrote:

In purchase model

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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

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

5

I have another problem

finally I used

In Purchase model

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

and it works fine, but now I’m trying to do something else with the
update. I mean, sometimes you can input some wrong data, so you need
to update values. So I was thinking in update the purchase.quantity
and then automagically update the product.quantity, so I tried this

def before_update
product.update_attribute(:quantity, product.quantity -
purchase.quantity)
end
def after_update
product.update_attribute(:quantity, product.quantity +
purchase.quantity)
end

but, that didn’t work, in both cases purchase.quantity is the new
value, and I need in the first case (before_update) the original value
and in the second case (after_update) the new value for
purchase.quantity

6

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

?

On Jul 20, 2011, at 23:55 , Angelo C. wrote:

current product.quantity = 5

product
end

I have 2 tables (models) “Product” and “Purchase”. I want to use the

===============================================================================
Tomas Meinlschmidt, MS {MCT, MCP+I, MCSE, AER}, NetApp Filer/NetCache

www.meinlschmidt.com www.maxwellrender.cz www.lightgems.cz

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www.meinlschmidt.com www.maxwellrender.cz www.lightgems.cz