rails has_many setter should set conditions if specified

问题

This seems like a bug in Rails to me, but there's probably not much I can do about that. So how can I accomplish my expected behavior?

Suppose we have:

class User < ActiveRecord::Base
  has_many :awesome_friends, :class_name => "Friend", :conditions => {:awesome => true}
end

And execute the code:

>> my_user.awesome_friends << Friend.new(:name=>'jim')

Afterwards, when I inspect this friend object, I see that the user_id field is populated. But I would also expect to see the "awesome" column set to 'true', which it is not.

Furthermore, if I execute the following from the console:

>> my_user.awesome_friends << Friend.new(:name=>'jim')
>> my_user.awesome_friends
= [#<Friend id:1, name:"jim", awesome:nil>]
# Quit and restart the console
>> my_user.awesome_friends
= []

Any thoughts on this? I suppose the conditions hash could be arbitrarily complex, making integration into the setter impossible. But in a way it feels like by default we are passing the condition ":user_id => self.id", and that gets set, so shouldn't others?

Thanks, Mike

EDIT:

I found that there are callbacks for has_many, so I think I might define the relationship like this:

has_many :awesome_friends,
         :class_name => "Friend",
         :conditions => {:awesome => true},
         :before_add => Proc.new{|p,c| c.awesome = true},
         :before_remove => Proc.new{|p,c| c.awesome = false}

Although, it's starting to feel like maybe I'm just implementing some other, existing design pattern. Maybe I should subclass AwesomeFriend < Friend? Ultimately I need a couple of these has_many relationships, and subclassing get's messy with all the extra files..

EDIT 2:

Okay, thanks to everyone who commented! I ultimately wrapped up the method above into a nice little ActiveRecord extension, 'has_many_of_type'. Which works like follows:

has_many_of_type :awesome_friends, :class_name => "Friend", :type=>:awesome

Which just translates to has_many with the appropriate conditions, before_add, and before_remove params (and it assumes the existence of a column named friend_type).

回答1:

You need use:

my_user.awesome_friends.create(:name=>'jim') or my_user.awesome_friends.build(:name=>'jim')

In documentation: has_many (:conditions)

Record creations from the association are scoped if a hash is used. has_many :posts, :conditions => {:published => true} will create published posts with @blog.posts.create or @blog.posts.build.

回答2:

It's :class_name rather than :class, for one thing.

回答3:

This isn't a bug I don't think. The :conditions hash only deterimines how you query for the objects. But I don't think it's rational to just assume that any object you stuff in the collection could be made to conform to the conditions.

In your simple example it makes sense, but you could also put more complex logic in there.

The documentation seems pretty clear on this as well:

http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html

:conditions

Specify the conditions that the associated object must meet in order to be included as a WHERE SQL fragment, such as authorized = 1.

来源：https://stackoverflow.com/questions/5785930/rails-has-many-setter-should-set-conditions-if-specified