Associations and Math between Models

Rails
1

I’ve setup two models, 1 and 2, that are associated by
has_and_belongs_to_many. I’m trying to get an attribute from model_1 to
use
in a method in model_2. When I use the code below, I get an error saying
‘undefined method model_1_id’. What am I missing? Thanks!

Model_2.rb

Class Model_2 < ActiveRecord::Base
…
has_and_belongs_to_many :model_1

def some_method
attr_a * Model_1.find(model_1_id).attr_I_need
end

2

On Tue, Sep 4, 2012 at 9:53 AM, sacshu [email protected] wrote:

When I use the code below, I get an error saying
‘undefined method model_1_id’. What am I missing? Thanks!

Class Model_2 < ActiveRecord::Base
…
has_and_belongs_to_many :model_1

def some_method
attr_a * Model_1.find(model_1_id).attr_I_need
end

Where do you think ‘model_1_id’ is being defined here?

–
Hassan S. ------------------------ [email protected]

twitter: @hassan

3

Well that’s kind of what I need help with, I’m not sure where it needs
to be defined in a many-to-many relationship. I’ve already created the
join table that contains both ids.

4

On Wed, Sep 5, 2012 at 1:00 PM, Sa S. [email protected] wrote:

Well that’s kind of what I need help with, I’m not sure where it needs
to be defined in a many-to-many relationship. I’ve already created the
join table that contains both ids.

The point is that your example makes no sense; you’ve defined this
as a “to-many” relationship – which Model_1 are you looking for?

–
Hassan S. ------------------------ [email protected]

twitter: @hassan

5

Hassan S. wrote in post #1074840:

On Wed, Sep 5, 2012 at 1:00 PM, Sa S. [email protected] wrote:

Well that’s kind of what I need help with, I’m not sure where it needs
to be defined in a many-to-many relationship. I’ve already created the
join table that contains both ids.

The point is that your example makes no sense; you’ve defined this
as a “to-many” relationship – which Model_1 are you looking for?

–
Hassan S. ------------------------ [email protected]
Hassan Schroeder | about.me
twitter: @hassan

Sorry, I should clarify. In my Model_2 view, I’m trying to simply have a
table that iterates through all the model_1’s and calculates that method
above using the model_1’s attribute that I need

6

On Wed, Sep 5, 2012 at 1:14 PM, Sa S. [email protected] wrote:

Sorry, I should clarify. In my Model_2 view, I’m trying to simply have a
table that iterates through all the model_1’s and calculates that method
above using the model_1’s attribute that I need

But you’re not showing us a view, you’re showing us a model.

Do you really want some_method to return one value or an array
of values?

If you only want one value, why don’t you pass the Model_1 instance
(or the attribute) you’re interested in to the Model_2 instance?

def some_method(model_1_attribute)
attr_a * model_1_attribute
end

–
Hassan S. ------------------------ [email protected]

twitter: @hassan