Access values with has_and_belongs_to_many assocciation


#1

Hi!
I have 2 models author and product.

class Author < ActiveRecord::Base
has_and_belongs_to_many :products
end

class Product < ActiveRecord::Base
has_and_belongs_to_many :authors
end

I have also created the migration for the jointable authors_products
with the keys author_id and product_id.

Now, i suppose that when i have eg an author with author_id = 1 and a
product_id=4 in the join table, i should be able to access the product
title of that product and the author name of my author.

How can i access these values???

Thanx in advance for your time!


#2

On Jun 1, 5:01 pm, LOUPOS KONSTANTINOS removed_email_address@domain.invalid wrote:

I have also created the migration for the jointable authors_products
with the keys author_id and product_id.

Now, i suppose that when i have eg an author with author_id = 1 and a
product_id=4 in the join table, i should be able to access the product
title of that product and the author name of my author.

How can i access these values???

The association adds some helper attributes to your model. If you
have an instance of an author you can use the products attribute to
get all of the associated products in an array:

my_author = Author.find(1)
my_author.products


#3

Thanx Brian.
So if i want to see the product title i should write
my_author.products.title??? Or i should use something else?
Cause i’ve tried it but i get nothing


#4

2009/6/3 Kostas L. removed_email_address@domain.invalid:

Thanx Brian.
So if i want to see the product title i should write
my_author.products.title??? Or i should use something else?
Cause i’ve tried it but i get nothing

my_author.products gives you an array of all the products for that
author, each of which has a title, so for example
my_author.products[0].title
will give you the title of the first one

Colin


#5

To get all the products titles of my_author you can do like

my_author.products.map(&:title)

Sijo


#6

Sijo,

map works great!
but is there any other way showing the title but not using map?
I am curious because i’ve been searching for this but i found nothing.

Thank u
Kostas

On Thu, Jun 4, 2009 at 7:08 AM, Sijo Kg
removed_email_address@domain.invalidwrote:


Κωνσταντίνος Λούπος
removed_email_address@domain.invalid


#7

Thanks!
Your help was really usefull!

On Thu, Jun 4, 2009 at 7:08 AM, Sijo Kg
removed_email_address@domain.invalidwrote:


Κωνσταντίνος Λούπος
removed_email_address@domain.invalid


#8

Thank u all.
Colin sorry for my previous question i found the sollution i wanted.
There is something else i want to do. I calculate the size of this
array. If
the size is less than 2, i want to see the name of the author, and if
there
are more than 2 authors i want to see both names with a party-comma
between
them.
here is the code so far:

<% if (product.authors.map(&:name).size) < 2 %>
<%= “Author: Here i should see the name of the author” %>
<% else %>
<%= “Authors: Here i should see all the authors name separated with a
party-comma.”%>
<% end %>

How can i do that?
Thank u for your time again!
Kostas

To get all the products titles of my_author you can do like


Κωνσταντίνος Λούπος
removed_email_address@domain.invalid


Κωνσταντίνος Λούπος
removed_email_address@domain.invalid


#9

2009/6/8 Konstantinos L. removed_email_address@domain.invalid:

<% else %>
<%= “Authors: Here i should see all the authors name separated with a
party-comma.”%>
<% end %>

No need to test for the special case of only one element, look up the
docs for Array#join and try something like
product.authors.map(&:name).join(’,’)
I am not sure what a party-comma is.
The only thing this won’t do is the s on the end of Author in the case
of multiple. So you may need to do the test if you really need this.
If so then product.authors.size < 2 will do, no need to convert it to
an array of names before checking the size.
There is one thing to watch out for though in both cases, suppose
product has no authors at all, then product.authors will be nil and
you would get an exception trying to call map or size on nil. In this
case you may want to display something else.
One way to tidy this up so you don’t end up with messy code in your
view would be to add a method to the product model that returns the
string you wish to see displayed and handles the nil case internally
then the view would just contain
<%= product.authors_text %>
where authors_text is product model method.

I think possibly you could usefully work through some basic tutorials
on Ruby to get you going.

Colin


#10

2009/6/6 Konstantinos L. removed_email_address@domain.invalid:

Sijo,

map works great!
but is there any other way showing the title but not using map?
I am curious because i’ve been searching for this but i found nothing.

What exactly do you mean by ‘showing the title’. The map function
returns an array containing the titles of all the products. What is
it that you are trying to achieve?

Colin