is possbile limit the number of object in has_many option?

rubyonrails-talk
1

(my post was deleted i don't know why) Hi. I have a question. for example, when model records about man, suppose man can marry with 1 woman. then i think code will be like this class Man < ActiveRecord::Base    has_many: wife end

Because one man can marry with up to 1 woman( 0 or 1 ) it can't be 1:1 relationship, didn't it? but at the same time more than 1 wife is not allowed. then how can i model this relationship into rails code? has_many :limit option is fit for this relation?

Thanks. and i wish it is not deleted again. If it should be deleted please let me know why it should be.

2

Did you consider

has_one :wife

And in Wife.rb

belongs_to :man

3

Did you consider

has_one :wife

And in Wife.rb

belongs_to :man

Or: class Wife

has_many :marriages

has_one :current_marriage, :class_name => ‘Marriage’, :conditions => { :current => true }

has_one :husband, :through => :current_marriage

end

class Marriage

belongs_to :wife

belongs_to :husband

end

class Husband

has_many :marriages

has_one :current_marriage, :class_name => ‘Marriage’, :conditions => { :current => true }

has_one :wife, :through => :current_marriage

end

-Rob

Rob Biedenharn http://agileconsultingllc.com

Rob@AgileConsultingLLC.com

4

thanks for replies. it gives me some thought about making active record association.

then what if the man is a single? husband may not have current_marriage. i was thinking that has_one means it should have one object. But as you know not every man will marry.

please more advice for this novice.

5

thanks for replies. it gives me some thought about making active record association.

then what if the man is a single? husband may not have current_marriage. i was thinking that has_one means it should have one object. But as you know not every man will marry.

please more advice for this novice.

Then, man.current_marriage will be nil as will man.wife

has_one really defines a 0/1 and has_many a 0/n relation.

-Rob

6

has_one does indeed mean has a maximum of one. The belongs_to side means has exactly one.

I don't know (because I never tried it) wjay happens if you put "belongs_to on both sides - i.e. make something exactly 1:1. Obviously not relevant in this case, but I could see situations where for performance reasons you may want that kind of partition - or when wrapping an external database.

C

7

has_one does indeed mean has a maximum of one. The belongs_to side means has exactly one.

I don't know (because I never tried it) what happens if you put "belongs_to on both sides - i.e. make something exactly 1:1. Obviously not relevant in this case, but I could see situations where for performance reasons you may want that kind of partition - or when wrapping an external database.

C

Belongs_to implies the presence of the foreign key so you can't have it on both models (unless you let them be out-of-sync while being created).

Has_one will only find one, but there could be many records that have the right foreign key. Just take any has_many association and change it to has_one (making the symbol singular, of course) and it will "just work" even though all the original records from the has_many are actually still there.

Notice how I defined has_many :marriages and has_one :current_marriage that both use the same Marriage model. Those all belongs_to :wife (and belongs_to :husband, too)

-Rob