Pre-load second level association?

Rails
1

Let’s say I have Customer -> Invoice -> OrderItem. All of those are
one-to-many.

Is there any way I can tell ActiveRecord than when I access
some_customer.invoices, AR should pre-load all the invoice.order_items
too, in one query, using a join? Similar to if I issued an :include
directive in a #find, but I’m not doing a manual find, I’m just accesing
some_customer.invoice. I want AR to automatically pre-load all of the
invoice’s order_items every time any code accesses
some_customer.invoice.

Is this something AR can do? If not, is there a common workaround to
get this efficiency? Is there a callback hook for after the
customer.invoices are loaded?

Thanks for any advice!

Jonathan

2

On 17 Apr 2008, at 21:20, Jonathan R. wrote:

invoice’s order_items every time any code accesses
some_customer.invoice.

you can say
has_many :foos, :include => :bars

Fred

3

Jonathan R. wrote:

Is this something AR can do? If not, is there a common workaround to
get this efficiency? Is there a callback hook for after the
customer.invoices are loaded?

Thanks for any advice!

Jonathan

in your Customer class…

has_many :invoices, :include => :order_items

Now, whenever you have @costumer, and you call @customer.invoices, then
the order_items will be eagerly loaded. You’re probably going to do
something more like @customer.invoices.find(params[:id]), and the above
will work with that too.

–

http://www.5valleys.com/

http://www.workingwithrails.com/person/8078

4

Thanks all, that did the trick. Good to know that works with an
association find too, nice.

Jon G. wrote:

Is there a callback hook for after the
customer.invoices are loaded?

in your Customer class…

has_many :invoices, :include => :order_items

Now, whenever you have @costumer, and you call @customer.invoices, then
the order_items will be eagerly loaded. You’re probably going to do
something more like @customer.invoices.find(params[:id]), and the above
will work with that too.