I have the following two models, User..
class User < ActiveRecord::Base
has_and_belongs_to_many :sites
end
.. and Site:
class Site< ActiveRecord::Base
has_and_belongs_to_many :users
end
Up to this point its fine. It works and it's pretty simple.
Now I want to introduce "primary user" to the Site. I add "primary_user_id" to the Site, and trying to add a second association:
class Site< ActiveRecord::Base
has_and_belongs_to_many :user
# my new association that doesn't work...
has_one :primary_user, :class_name => "User", :conditions => ['id = ?', '{self.primary_user_id}']
end
It doesn't like it... Now I know that I can fake this by just adding a method "primary_user" to the site and this will work, but my question is whether it is possible to user ActiveRecord associations and how?
has_and_belongs_to_many is tricky and most people have moved away from it and use has_many through => model.
btw - 'Up to this point its fine. It works and it's pretty simple.' is how all things start off. How they perform when you 'really' start to use them is what counts and for that reason you'll probably find has_many through easier to work with.
These links will help:
http://paulbarry.com/articles/2007/10/24/has_many-through-checkboxes
http://thoughtsincomputation.com/posts/checkboxes-with-has_many-through
http://my.opera.com/durrantm/blog/2011/07/24/rails-simple-form-with-has-many-through-hmt-relationship
https://github.com/romanvbabenko/nested_has_many_through (nesting gem).
Related
I'm looking for some suggestions on how to deal with "Regions" in my system.
Almost all other models in the system (news, events, projects, and others) need to have a region that they can be sorted on.
So far, I've considered a Region model with has_many :through on a RegionLink table. I've never had a model joined to so many others and wonder if this route has any negatives.
I've also considered using the acts_as_taggable_on gem and just tag regions to models. This seems ok but I'll have to write more cleanup type code to handle the customer renaming or removing a region.
Whatever I choose I need to handle renaming and, more importantly, deleting regions. If a region gets deleted I will probably just give the user a choice on another region to replace the association.
Any advice on handling this is greatly appreciated.
If each News, Event, etc. will belong to only 1 Region, tags don't seem the most natural fit IMO. This leaves you with 2 options:
Add a region_id field to each model
This is simplest, but has the drawback that you will not be able to look at all the "regioned" items at once - you'll have to query the news, events, etc. tables separately (or use a UNION, which ActiveRecord doesn't support).
Use RegionLink model with polymorphic associations
This is only slightly more complicated, and is in fact similar to how acts_as_taggable_on works. Look at the Rails docs on *belongs_to* for a fuller description of polymorphic relationships if you are unfamiliar
class Region < ActiveRecord::Base
has_many :region_links
has_many :things, :through => :region_links
end
# This table with have region_id, thing_id and thing_type
class RegionLink < ActiveRecord::Base
belongs_to :region
belongs_to :thing, :polymorphic => true
end
class Event < ActiveRecord::Base
has_one :region_link, :as => :thing
has_one :region, :through => :region_link
end
# Get all "things" (Events, Projects, etc.) from Region #1
things = Region.find(1).things
Renaming is quite simple - just rename the Region. Deleting/reassigning regions is also simple - just delete the RegionLink record, or replace it's region_id.
If you find yourself duplicating a lot of region-related code in your Event, etc. models, you may want to put it into a module in lib or app/models:
module Regioned
def self.inluded(base)
base.class_eval do
has_one :region_link, :as => :thing
has_one :region, :through => :region_link
...
end
end
end
class Event < ActiveRecord::Base
include Regioned
end
class Project < ActiveRecord::Base
include Regioned
end
Checkout the cast about polymorphic associations. They did change a bit in rails 3 though: http://railscasts.com/episodes/154-polymorphic-association?view=asciicast
I am trying to add a condition to a has many through association without luck. This is the association in my video model:
has_many :voted_users, :through => :video_votes, :source => :user
I want to only get the voted_users whose video_votes have a value equal to 1 for that video. How would I do this?
I would suggest creating a model method within the video model class
Something like:
def users_with_one_vote
self.voted_users, :conditions => ['value = ?', 1]
end
Then in the controller use video.users_with_one_vote
Then testing is easier too.
Any chance you can change that column name from 'value'. Might give some issues (reserved?).
I'd do this in 2 stages:
First, I'd define the has_many :through relationship between the models without any conditions.
Second, I'd add a 'scope' that defines a where condition.
Specifically, I'd do something like:
class User < ActiveRecord::Base
has_many :video_votes
has_many :votes, :through=>:video_votes
def self.voted_users
self.video_votes.voted
end
end
class VideoVote
def self.voted
where("value = ?", 1)
end
end
class Video
has_many :video_votes
has_many :users, :through=>:video_votes
end
Then you could get the users that have voted using:
VideoVote.voted.collect(&:user).uniq
which I believe would return an array of all users who had voted. This isn't the exact code you'd use -- they're just snippets -- but the idea is the same.
Would
has_many :voted_users, :through => :video_votes, :source => :user, :conditions => ['users.votes = ?', 1]
Do the trick?
I found that defining this method in my model works:
def upvoted_users
self.voted_users.where("value = 1")
end
and then calling #video.upvoted_users does the trick.
The best way to do this without messing with the relations is by crafting a more complex query. Relations is not the best thing to use for this particular problem. Please understand that relations is more a "way of data definition" then a way of "bussiness rules definition".
Bussiness logic or bussiness rules must be defined on a more specifically layer.
My suggestion for your problem is to create a method to search for users who voted on your video only once. something like:
class Video < ActiveRecord::Base
def voted_once()
User.joins(:video_votes).where("video_votes.value == 1 AND video_votes.video_id == ?", this.id)
end
Rails is magical for many things, but complex queries still have to be done in a "SQL" way of thinking. Don't let the illusional object oriented metaphor blind you
As long as we are throwing around ideas, how about using association extensions.
class VideoVote
scope :upvotes, where(:value => 1)
end
class Video
has_many :voted_users, :through => :video_votes, :source => :user do
def upvoted
scoped & VideoVote.upvotes
end
end
end
Then you feel good about making a call with absolutely no arguments AND you technically didn't add another method to your Video model (it's on the association, right?)
#video.voted_users.upvoted
I have the following classes:
class Region < ActiveRecord::Base
has_many :geographical_relations, :as => :contained
has_many :geographical_units, :as => :container, :class_name => "GeographicalRelation"
end
class GeographicalRelation < ActiveRecord::Base
belongs_to :container, :polymorphic => true
belongs_to :contained, :polymorphic => true
end
class Country < ActiveRecord::Base
has_many :geographical_relations, :as => :contained
end
And I want to be able to, from a Country record, get all the Regions in which it is contained:
c = Country.find(1)
c.regions #=> should return all the regions in which c is contained
For now I've created the following method:
def regions
self.geographical_relations.where(:container_type => "Region").map{|relation| relation.container}
end
But I wonder if there's any way to set an "has_many" association to do this for me.
Cheers.
EDIT:
after trying the alternatives suggested in the comments I only got nice ActiveRecord errors.
The has_many_polymorphs gem seems to be a good way to do this, but for Rails 3 it is not 'officially' supported so for my case it is not a good option.
So I will work with methods like the one described above, putting them in modules and including the respective modules inside each "container"/"contained" models. This seems to work ok. =) Only change I made, to avoid N+1 Queries was adding 'includes':
def regions
self.geographical_relations.includes(:container).where(:container_type => "Region").map{|relation| relation.container}
end
Hopefully this works nicely and fast... =P =)
Anyway if anyone has an answer to solve this I'll look forward to see it! =)
Thanks all!
I'm using a :has_many, :through association to link two models, User and Place
It looks like this -
In User:
has_many :user_places
has_many :places, :through=>:user_places
In Place:
has_many :user_places
has_many :users, :through=>:user_places
In User_Place
belongs_to :user
belongs_to :place
belongs_to :place_status
On that last one note the place_status.
I want to write a find that returns all places associated to a user with a particular place_status_id.
Place_Status_id is on the join model, user_place.
So basically I want
User.places.where(:place_status_id=>1)
(in rails 3)
but i get an error with that because place_status_id isnt on the place model.
Any ideas? Thanks all.
I believe you can do your find this way
#user.places.joins(:user_places).where(:user_places => {:place_status_id => 1})
I've never used Rails 3, so I'm sorry if there's any errors.
I have the following setup:
class Publication < ActiveRecord::Base
has_and_belongs_to_many :authors, :class_name=>'Person', :join_table => 'authors_publications'
has_and_belongs_to_many :editors, :class_name=>'Person', :join_table => 'editors_publications'
end
class Person < ActiveRecord::Base
has_and_belongs_to_many :publications
end
With this setup I can do stuff like Publication.first.authors. But if I want to list all publications in which a person is involved Person.first.publications, an error about a missing join table people_publications it thrown. How could I fix that?
Should I maybe switch to separate models for authors and editors? It would however introduce some redundancy to the database, since a person can be an author of one publication and an editor of another.
The other end of your associations should probably be called something like authored_publications and edited_publications with an extra read-only publications accessor that returns the union of the two.
Otherwise, you'll run in to sticky situations if you try to do stuff like
person.publications << Publication.new
because you'll never know whether the person was an author or an editor. Not that this couldn't be solved differently by slightly changing your object model.
There's also hacks you can do in ActiveRecord to change the SQL queries or change the behavior of the association, but maybe just keep it simple?
I believe you should have another association on person model
class Person < ActiveRecord::Base
# I'm assuming you're using this names for your foreign keys
has_and_belongs_to_many :author_publications, :foreign_key => :author_id
has_and_belongs_to_many :editor_publications, :foreign_key => :editor_id
end