Using ActiveRecord Find with associations

[Pito Salas]

Here's an example:

class LineItem < ActiveRecord::Base
belongs_to :order
end

class Order < ActiveRecord::Base
has_many :line_items
end

my_line_item = LineItem.find(:zipcode => "12345")

Order.find_by_line_item(my_line_item) # doesn't work

Order.find_by_line_item_id (my_line_item) # does work

I was surprised by this, because it seems to force me to make reference
to the id field of the line item, rather than referring to the LineItem
as a class or type in the Order.findxxx statement.

Am I misunderstanding something or missing a trick?

Thanks!!

-- Pito
--
Posted via http://www.ruby-forum.com/.

[Ar Chron]

Pito Salas wrote:
> Here's an example:
>
> class LineItem < ActiveRecord::Base
> belongs_to :order
> end
>
> class Order < ActiveRecord::Base
> has_many :line_items
> end
>
> my_line_item = LineItem.find(:zipcode => "12345")
>
> Order.find_by_line_item(my_line_item) # doesn't work
>
> Order.find_by_line_item_id (my_line_item) # does work
>

Probably not explaining this clearly enough (I blame the distillery
masters at Lagavulin), but:

find_by_line_item fails - my_line_item is an instance of the class (an
object) that does not have a 'line_item' attribute you indicated, it
*is* a LineItem

find_by_line_item_id works - rails infers the id attribute when you pass
an object (my_line_item), and in this case you've provided enough
information to tell rails which attribute to use...

I suppose you could mod the logic for find to include your syntax...

[Pito Salas]

Ar Chron wrote:
> Pito Salas wrote:
>> Here's an example:
>>
>> class LineItem < ActiveRecord::Base
>> belongs_to :order
>> end
>>
>> class Order < ActiveRecord::Base
>> has_many :line_items
>> end
>>
>> my_line_item = LineItem.find(:zipcode => "12345")
>>
>> Order.find_by_line_item(my_line_item) # doesn't work
>>
>> Order.find_by_line_item_id (my_line_item) # does work
>>
>
> Probably not explaining this clearly enough (I blame the distillery
> masters at Lagavulin), but:

Wish I was there! Which of their Beer is available in the US?

>
> find_by_line_item fails - my_line_item is an instance of the class (an
> object) that does not have a 'line_item' attribute you indicated, it
> *is* a LineItem

It kind of does, in that Order has_many :line_items, no? And so that's
an ActiveRecord method on Order called line_items?

By the way, my_order.find_by_line_item fails with "no such method", not
just by returning [].

I wonder if my_order.find_by_line_items would work?

[KlausG]

> > Probably not explaining this clearly enough (I blame the
distillery
> > masters at Lagavulin), but:
>
> Wish I was there! Which of their Beer is available in the US?
>

Lol, Lagavulin is a famous WHISKY destillery

>
>
> By the way, my_order.find_by_line_item fails with "no such method", not
> just by returning [].
>

ActiveRecord knows that your line_item belongs to an order.
So it's as easy as:
my_line_item.Order

[pepe]

As I am sure you know the 'find_by*' methods are all dynamic. They are
based on the field/column name, not on the type of object the column
is supposed to reference (if any). AR will do the magic of finding the
ID value if you pass an object to the method but apparently it will
not be "magic enough" to let you remove the '_id' suffix from the
field/column name in your 'find_by*' method name. It would be nice if
the Rails guys made a little change so we could do what you wanted to
do here, though. ;)

[Colin Law]

On 4 September 2010 01:27, Pito Salas <li...@ruby-forum.com> wrote:
> Here's an example:
>
> class LineItem < ActiveRecord::Base
>  belongs_to :order
> end
>
> class Order < ActiveRecord::Base
>  has_many :line_items
> end
>
> my_line_item = LineItem.find(:zipcode => "12345")
>
> Order.find_by_line_item(my_line_item) # doesn't work
>
> Order.find_by_line_item_id (my_line_item) # does work
>
> I was surprised by this, because it seems to force me to make reference
> to the id field of the line item, rather than referring to the LineItem
> as a class or type in the Order.findxxx statement.
>
> Am I misunderstanding something or missing a trick?

I think you are missing a trick. Once you have my_line_item, to get
the item's order just do
my_line_item.order
There is no need to use find at all.

Colin