Quick simple check: Very simple relationship setup (newbish for sure.)

rubyonrails-talk
1

Been googling trying to understand belongs_to, has_one, etc

For this scenario: 'A Person has a single favorite color and has multiple addresses. (Colors are reused across all the persons, addresses are always unique only for one person)'

Would the following suffice? (not worrying about adding indexes yet.)

class Person < ActiveRecord::Base   belongs_to :favorite_color, :class_name => "Color", :foreign_key => "color_id"   has_many :addresses, :dependent => :destroy end

class Address < ActiveRecord::Base   belongs_to :product end

class Color < ActiveRecord::Base   #don't need anything end

The toughest thing conceptually to get a handle on was "belongs_to" on something like Color. From an OO perspective a Person "has_one" Color, but from reading the docs I see that belongs_to puts the foreign key on that table in the class where you declare belongs_to so in the above it belongs on Person. (From an OO perspective the Address 'belongs_to' a Person makes sense.)

2

Looking at what you provides so far let's go ahead and diagram it exactly the way you wrote it and see what's wrong here. I'm leaving off activerecord base for sake of clarity...

class Person belongs_to :favorite_color, :class_name => "Color", :foreign_key => "color_id" has_many :addresses, :dependent => :destroy end

class Address belongs_to :product end

class Color #don't need anything end

=============================

First thing I don't see is your relationship models for Product or FavoriteColor. So, creating them based off what you wrote above I see:

class Product has_many :addresses end

class FavoriteColor has_many :persons has_many :addresses, :through => :persons end

I thought I could do: belongs_to :favorite_color, :class_name => "Color", :foreign_key => color_id

Which tells it to use the Color class for favorite_color ? I don't want a FavoriteColor model, just Color. I could have just used: class Person    belongs_to :color If I was content with a color_id column name for favorite color on Person.

But, you have class Address belonging to Product but your association for Person is stating that addresses belong to it. Which does address really belong to?

Well the reason I added Addresses 'belonging to" Product is so that it would put the FK product_id in the Address table. I guess I should just leave off belongs_to :person on the Address model?

3

And thanks for the links by the way.

But looking at the second link they show:

class Customer < ActiveRecord::Base    has_many :orders, :dependent => :destroy end

class Order < ActiveRecord::Base    belongs_to :customer end

How is that any different than my association for Person and Address (which you said was wrong)?

class Person < ActiveRecord::Base   has_many :addresses, :dependent => :destroy end

class Address < ActiveRecord::Base belongs_to :product end

It looks the same as it does in the doc, unless I'm missing something?

4

Rick wrote:

And thanks for the links by the way.

But looking at the second link they show:

class Customer < ActiveRecord::Base    has_many :orders, :dependent => :destroy end

class Order < ActiveRecord::Base    belongs_to :customer end

How is that any different than my association for Person and Address (which you said was wrong)?

class Person < ActiveRecord::Base   has_many :addresses, :dependent => :destroy end

class Address < ActiveRecord::Base belongs_to :product end

It looks the same as it does in the doc, unless I'm missing something?

end

end

But, you have class Address belonging to Product but your association for Person is stating that addresses belong to it. �Which does address really belong to?

Well the reason I added Addresses 'belonging to" Product is so that it would put the FK product_id in the Address table. �I guess I should just leave off belongs_to :person on the Address model?

-- Rick R

Hi Rick,

Thanks for looking at the links and thanks for the clarifications. I missed your Color class association so that part is fine.

Looking at the Customer - Order association you placed here..

Customer --> Has Many --> Orders Orders --> Belongs to --> Customer

That's a correct association...

Now look at yours:

Person --> Has Many --> Addresses Address --> Belongs to --> (PRODUCT)?

Notice there's no correct association here...

Anytime you you have a name_id in any of your tables, rails automatically knows it's a foreign key once you apply the association.

Person has many addresses Address belongs to person Product has many addresses Address belongs to product

That sound about right?

Class Person   has_many :addresses, :dependent => :destroy end Class Address   belongs_to :person   belongs_to :product end Class Product   has_many :addresses end

5

Using what I posted above you need to have the following:

In your Address model you need to have a

person_id product_id

If you want these foreign keys to be different you can do the following:

Class Address   belongs_to :person   belongs_to :product :foreign_key => uniquesomething_id end

Whatever foreign_key you use, needs to be setup correctly in the table which belongs to the other table.

It really comes down to whatever you want to do and that's why diagraming is good because it allows you to see what you have before you implement things to make sure they work well.

6

UGGHHHH! I feel so bad.

Stupid copy and paste error! Amazing I could be staring at something and not even see it.

I was translating something else into Person/Color/Address from what I was working with "Product" and totally screwed up and put Product down since it was on my mind instead of Person.

So sorry for the confusion! And thanks so much for your patience and help. I can't believe I was mentally translating Product into Person in my head:)

I meant to have:

class Address < ActiveRecord::Base      belongs_to :product end

That makes more sense now I bet:) Apologies again.

7

Ha i did it again sorry:

class Address < ActiveRecord::Base     belongs_to :person #!!!!!!!!!!!!!!!   end

Ok it's Friday I need to go away !