Suppose I have the following model relationship:
class Player < ActiveRecord::Base
has_many :cards
end
class Card < ActiveRecord::Base
belongs_to :player
end
I know from this question that Rails will return me a copy of the object representing a database row, meaning that:
p = Player.find(:first)
c = p.cards[0]
c.player.object_id == p.object_id # => false
...and therefore if the Player model modifies self, and the Card model modifies self.player in the same request, then the modifications won't take any notice of each other and the last-saved one will overwrite the others.
I'd like to work around this (presumably with some form of caching), so that all requests for a Player with a given id would return the same object (identical object_ids), thereby allowing both models to edit the same object without having to perform a database save-and-reload. I have three questions:
Is there already a plugin or gem to do this?
Are there good reasons why I shouldn't do this?
Can anyone give me some pointers on how to go about doing this?
This is supported in Rails 3.x. You can use the :inverse_of option for the has_many association for example. Documentation here (search for :inverse_of and Bi-directional associations).
Related
I have a polymorphic association in a Rails 3 app where a User may favorite objects of various classes.
class Favorite < ActiveRecord::Base
belongs_to :user
belongs_to :favoriteable, :polymorphic => true
end
class User < ActiveRecord::Base
has_many :favorites
end
class Image < ActiveRecord::Base
has_many :favorites, :as => :favoriteable
end
class Video < ActiveRecord::Base
has_many :favorites, :as => :favoriteable
end
I would like to be able return a list of just a User's favorite_images for example.
user.favorite_images #returns a list of the images associated with the user via :favoritable
I'm guessing there is a straightforward way of doing this but I haven't been able to figure it out. Let me know if you need anymore info.
Thanks!
===edit====
I know that I could retrieve what I am looking for via
favorite_images = user.favorites.collect{|f| if f.favoriteable_type=='Image'; f.favoriteable; end}
I could define an instance method for the User class and put that inside. I was wondering if there is a way to do it as some sort of has_many association. Really just because going forward it would be easier to have all that in one place.
When you created the table for Favorite you created a couple of columns favoriteable_id and favoriteable_type and you can use this information to restrict your query.
If you do user.favorites you will get all of the favorites and to restrict them to say just the images then you can do user.favorites.where(favoriteable_type: 'image') but that just gives you the favorite records and it sounds like you want the actual images. To get those you can do it by then mapping and pulling the favoriteable out. You'll likely want to include it in the query though so you don't hit the database so much. I would also make this a method on User.
def favorite_images
favorites.includes(:favoriteable).where(favoriteable_type: 'Image').map(&:favoriteable)
end
I have two models that are connected via a has_many/belongs_to association:
Class Project < ActiveRecord::Base
has_many :tasks
end
Class Tasks < ActiveRecord::Base
belongs_to :project
end
Each of the tasks are tagged with a HABTM relationship:
Class Tasks < ActiveRecord::Base
belongs_to :project
has_and_belongs_to_many :tags
end
I am trying to get a list of projects based on a tag id. I can get a list of projects that have tasks with a specific tag by using a class method on my Project model:
def by_tag(tag_id)
Project.joins(:tasks => :tags).where(:tags => {:id = tag_id})
end
Ideally, I'm looking to be able to list all the projects and their associated tasks for a given tag in my view. I could normally get a list of tasks belonging to a given project by using project.tasks if I used a typical find with project like Project.find(1).
However, when I try project.tasks on results found using my new class method Project.by_tag(1), I get a "NoMethodError: Undefined Method 'tasks'" error.
I looked into Named Scopes to get the Project by Tag results but it seems like people are moving away from that approach in favor of class methods. Is that true?
On your project model you need to add it to the class not the instance. Also note that this raises the self object to the class so you can eliminate "Project." unless you want to be explicit.
class << self
def by_tag(tag_id)
joins(:tasks => :tags).where(:tags => {:id = tag_id})
end
end
There is always debate over what is the best method. I myself prefer whatever gets the job done quicker. I like scopes personally but to each his own.
I made a relationship with the three models using has_many :through:
class Curriculum class < ActiveRecord::Base
has_many :interests
has_many :vacancies,: through => :interests
end
class Vacancy class < ActiveRecord::Base
has_many :interests
has_many :resumes,: through => :interests
end
class Interest < ActiveRecord:: Base
belongs_to :vacancy
belongs_to :curriculum
end
And to create curriculum and vacancy, I create them by administrative, i need to know how can i create the interest to the id of the vacancy, and how it will be logged on the system I have to get the id of it and make the relationship in creating a new bank interest. I wonder how I can program it to do so, and I wonder how the controller will get the create action, and what better way to do this.
First, try to read the whole "Guide to Rails on Associations", especially the part about has_many :through. Then check your schema if your db is migrated and contains for the table interests the necessary foreign keys to curriculums and vacancies called curriculum_id and vacancy_id.
If that is all in place, the following code will create the relationship between two objects:
#curr = Curriculum.find(1)
#vac = Vacancy.find(1)
#curr.interests << #vac
#curr.save
The last two lines creates an interest between #curr and #vac and store that on the database. So you should not use IDs and handle them directly, but work with objects instead.
The second part now is to provide a UI to allow the definition (and removal) of interests between curricula and vacancies. The base flow here is:
You have one curriculum in focus.
You have a link to add / remove curricula.
The view that opens shows a list of possible vacancies, where every vacancy has a checkbox.
By selecting (or deselecting) the check boxes, the IDs of the vacancies will be held in the params of the request sent to the controller.
See the (older) podcast Railscast #52 how to do that in a similar context. Or see the example for has_many :through with checkboxes.
An alternative way would be to use JQuery autocomplete, and add so interests one-by-one. See the nice podcast Railscast #258 which uses JQuery Tokeninput for that.
I think this is what your looking for:
HABTM Checkboxes
That's the best way to use an Has and Belongs to many association.
I have a need to add metadata about a HABTM relationship. I wanted to use a has_many :through relationship to accomplish this, but it is not necessary. Here is the problem simplified:
class Customer < ActiveRecord::Base
has_many :customer_teddy_bears
has_many :teddy_bears, :through => :customer_teddy_bears
end
class CustomerTeddyBear < ActiveRecrod::Base
belongs_to :customer
belongs_to :teddy_bear
attr_accesible :most_favoritest # just to show it exists, boolean
end
class TeddyBear < ActiveRecord::Base
has_many :cusomter_teddy_bears
end
So what I need to do is start adding teddy bears to my customers, Teddy Bears are a fixed set of data, lets say a fireman_bear, doctor_bear, dominatrix_bear. Any customer can claim to own a kind of teddy bear, but they also specify which is their most favoritest bear. Since I cannot modify the bears model because that is globally shared among all customers I am adding the metadata (among other metadata) to CustomerTeddyBear.
The problem is that the following does not work.
customer = Customer.new # new record, not yet saved, this must be handled.
customer.teddy_bears << fireman_bear
customer.teddy_bears << doctor_bear
# now to set some metadata
favoritest_record = customer.customer_teddy_bears.select{|ctb| ctb.teddy_bear == doctor_bear}.first
favoritest_record.most_favoritest = true
The above code does not work since customer_teddy_bears entries are only populated during save when creating records in the database. Is there another mechanism for doing this?
If there is nothing "automated" built into rails I will just have to manually manage this relationship by including teddy_bears when I select customer_teddy_bears and using techniques like
def teddy_bears
self.customer_teddy_bears.map(&:teddy_bear)
end
along with manually creating the associations, and not using a :through relationship.
please note, all this must happen before the #save is executed on the Customer object, so I need to set all relevant metadata while still in-memory.
Recommendations I got from #RubyOnRails
ctb = customer.customer_teddy_bears.build({:customer => customer, :teddy_bear => fireman_bear})
ctb2 = customer.customer_teddy_bears.build({:customer => customer, :teddy_bear => doctor_bear})
...
ctb.most_favoritest = true
You can simply do this:
customer = Customer.new # new record, not yet saved, this must be handled.
customer.teddy_bears << fireman_bear
customer.teddy_bears << doctor_bear
customer.save
fav = CustomerTeddyBear.where(:customer_id => customer.id, :teddybear_id => doctor_bear.id)
fav.most_favoritest = true
fav.save
The solution I was forced to resort to is manually building the CustomerTeddyBear object and setting both the customer, teddy_bear, and most_favoritest. Basically most of the time, access is by customer.customer_teddy_bears.map(&:teddy_bear) at least in logic where the possibility is that the record is not yet saved, otherwise just short-cut to customer.teddy_bears.
I am getting still this error, Setting and Paymentshop are models.
class Setting < ActiveRecord::Base
has_many :paymentshops
end
class PaymentShop < ActiveRecord::Base
belongs_to :setting
end
In view I have problem on this line:
dopr.paymentshops.type_v
dopr is variable with data from Setting and type_v is column in table Paymentshops.
I would like to ask you, If could anyone help me please with this error...
Thanks
Rails tries to automatically infer the model name from the relation name. With no indication of where to break the single lower-case stream of characters, it assumes that the target model is called Paymentshops.
You can explicitly override the expected class name with has_many :paymentshops, :class_name => "PaymentShop". Alternatively, you could try using has_many :payment_shops - I'm not 100% sure how Rails modifies the relation names, but I think that should map to PaymentShop directly.