I have three models which look something like this:
Class User < ActiveRecord::Base
has_many :comments
end
Class Comment < ActiveRecord::Base
belongs_to :user
has_many :votes
end
Class Vote < ActiveRecord::Base
belongs_to :comment
end
Now I want to get all the votes associated with a user's comments like so:
#user.comments.votes
But this throws the error:
undefined method `votes' for #<ActiveRecord::Relation:0x3f6f8a0>
This seems like it should work, but I suspect ActiveRecord is coughing on the deeper has_many relationship. I've hacked together an SQL query that gets the desired results, but I suspect there's a cleaner way using purely ActiveRecord. Any tips?
You should use a has_many :through association
In your case it would be
Class User < ActiveRecord::Base
has_many :comments
has_many :votes, :through => :comments
end
Class Comment < ActiveRecord::Base
belongs_to :user
has_many :votes
end
Class Vote < ActiveRecord::Base
belongs_to :comment
end
And then simply get the votes with
#user.votes
Try this:
Vote.joins(comment: :user).where(users: {id: #user.id})
Related
I'm trying to query on ActiveRecord multiple nested eager loaded associations with conditions like so:
user.books.includes(slot: [room: :school]).where("books.slot.room.school.id = 1")
Obviously this query is wrong, but basically what I'm trying to reach is a relation of user.books for a certain school.
My model structure is:
class User < ActiveRecord::Base
has_many :books
has_many :slots, through: :books
has_many :rooms, through: :slots
has_many :schools
end
class Book < ActiveRecord::Base
belongs_to :user
belongs_to :slot
end
class Slot < ActiveRecord::Base
has_many :books
belongs_to :room
end
class Room < ActiveRecord::Base
belongs_to :school
has_many :slots
end
class School < ActiveRecord::Base
has_many :users
has_many :rooms
has_many :slots, through: :rooms
has_many :books, through: :slots
end
Any ideas? Thanks in advance.
includes eager loads association records, while joins does what you want to do.
This question has been asked here numerous times. Please make sure that you look and try to find a similar question here before you ask one.
So you want to change your code like this:
user.books.joins(slot: [room: :school]).where(schools: { id: 1 })
Here is my models:
class User < ActiveRecord::Base
has_many :products
has_many :comments
end
class Product < ActiveRecord::Base
belongs_to :user
has_many :comments
end
class Comment < ActiveRecord::Base
belongs_to :user
belongs_to :product
end
I need to get comment records from current user products only
How do I do that? thanks
If we move the relationships to use a has_many: comments, through: products you can probably get what you're after:
class User < ActiveRecord::Base
has_many :products
has_many :comments, through: products
end
class Product < ActiveRecord::Base
belongs_to :user
has_many :comments
end
class Comment < ActiveRecord::Base
belongs_to :user
belongs_to :product
end
Now you can do user.comments.
The rails docs are here, which say:
A has_many :through association is often used to set up a many-to-many
connection with another model. This association indicates that the
declaring model can be matched with zero or more instances of another
model by proceeding through a third model. For example, consider a
medical practice where patients make appointments to see physicians.
The Ruby on Rails app I am working on allows users to create and share agendas with other users.
In addition, we must be able to:
Display a list of agendas for each user, on his profile
Display a list of users associated with an agenda, on the agenda's page
When sharing an agenda with another user, define a role for this user, and display the role of this user on the list mentioned right above
I was going to go with a has_and_belongs_to_many association between the user and the agenda models, like that:
class User < ActiveRecord::Base
has_and_belongs_to_many :agendas
end
class Agenda < ActiveRecord::Base
has_and_belongs_to_many :users
end
But then I wondered whether this would let me get and display the #user.agenda.user.role list of roles on the given agenda page of a given user.
And I thought I should probably go with a has_many :through association instead, such as:
class User < ActiveRecord::Base
has_many :roles
has_many :agendas, through: :roles
end
class Role < ActiveRecord::Base
belongs_to :user
belongs_to :agenda
end
class Agenda < ActiveRecord::Base
has_many :roles
has_many :users, through: :roles
end
And although I was pretty comfortable about the idea of a user having several roles (one for each agenda), I am not sure about the idea of an agenda having several roles (one for each user?).
Finally, to add to the confusion, I read about the polymorphic association and thought it could also be a viable solution, if done this way for instance:
class Role < ActiveRecord::Base
belongs_to :definition, polymorphic: true
end
class User < ActiveRecord::Base
has_many :roles, as: :definition
end
class Agenda < ActiveRecord::Base
has_many :roles, as: :definition
end
Does any of the above solutions sound right for the situation?
UPDATE: Doing some research, I stumbled upon this article (from 2012) explaining that has_many :through was a "smarter" choice than has_and_belongs_to_many. In my case, I am still not sure about the fact that an agenda would have many roles.
UPDATE 2: As suggested in the comments by #engineersmnkyn, a way of solving this would be to go with two join tables. I tried to implement the following code:
class User < ActiveRecord::Base
has_many :agendas, through: :jointable
end
class Agenda < ActiveRecord::Base
end
class Role < ActiveRecord::Base
end
class Jointable < ActiveRecord::Base
belongs_to :user
belongs_to :agenda
has_many :agendaroles through :jointable2
end
class Jointable2 < ActiveRecord::Base
belongs_to :roles
belongs_to :useragenda
end
I am not sure about the syntax though. Am I on the right track? And how should I define the Agenda and the Role models?
UPDATE 3: What if I went with something like:
class User < ActiveRecord::Base
has_many :roles
has_many :agendas, through: :roles
end
class Role < ActiveRecord::Base
belongs_to :user
belongs_to :agenda
end
class Agenda < ActiveRecord::Base
has_many :roles
has_many :users, through: :roles
end
and then, in the migration file, go with something like:
class CreateRoles < ActiveRecord::Migration
def change
create_table :roles do |t|
t.belongs_to :user, index: true
t.belongs_to :agenda, index: true
t.string :privilege
t.timestamps
end
end
end
Would I be able to call #user.agenda.privilege to get the privilege ("role" of creator, editor or viewer) of a given user for a given agenda?
Conversely, would I be able to call #agenda.user.privilege ?
Okay I will preface by saying I have not tested this but I think one of these 2 choices should work well for you.
Also if these join tables will never need functionality besides a relationship then has_and_belongs_to_many would be fine and more concise.
Basic Rails rule of thumb:
If you need to work with the relationship model as its own entity, use has_many :through. Use has_and_belongs_to_many when working with legacy schemas or when you never work directly with the relationship itself.
First using your example (http://repl.it/tNS):
class User < ActiveRecord::Base
has_many :user_agendas
has_many :agendas, through: :user_agendas
has_many :user_agenda_roles, through: :user_agendas
has_many :roles, through: :user_agenda_roles
def agenda_roles(agenda)
roles.where(user_agenda_roles:{agenda:agenda})
end
end
class Agenda < ActiveRecord::Base
has_many :user_agendas
has_many :users, through: :user_agendas
has_many :user_agenda_roles, through: :user_agendas
has_many :roles, through: :user_agenda_roles
def user_roles(user)
roles.where(user_agenda_roles:{user: user})
end
end
class Role < ActiveRecord::Base
has_many :user_agenda_roles
end
class UserAgenda < ActiveRecord::Base
belongs_to :user
belongs_to :agenda
has_many :user_agenda_roles
has_many :roles, through: :user_agenda_roles
end
class UserAgendaRoles < ActiveRecord::Base
belongs_to :role
belongs_to :user_agenda
end
This uses a join table to hold the relationship of User <=> Agenda and then a table to join UserAgenda => Role.
The Second Option is to use a join table to hold the relationship of User <=> Agenda and another join table to handle the relationship of User <=> Agenda <=> Role. This option will take a bit more set up from a CRUD standpoint for things like validating if the user is a user for that Agenda but allows a little flexibility.
class User < ActiveRecord::Base
has_many :user_agendas
has_many :agendas, through: :user_agendas
has_many :user_agenda_roles
has_many :roles, through: :user_agenda_roles
def agenda_roles(agenda)
roles.where(user_agenda_roles:{agenda: agenda})
end
end
class Agenda < ActiveRecord::Base
has_many :user_agendas
has_many :users, through: :user_agendas
has_many :user_agenda_roles
has_many :roles, through: :user_agenda_roles
def user_roles(user)
roles.where(user_agenda_roles:{user: user})
end
end
class Role < ActiveRecord::Base
has_many :user_agenda_roles
end
class UserAgenda < ActiveRecord::Base
belongs_to :user
belongs_to :agenda
end
class UserAgendaRoles < ActiveRecord::Base
belongs_to :role
belongs_to :user
belongs_to :agenda
end
I know this is a long answer but I wanted to show you more than 1 way to solve the problem in this case. Hope it helps
For some reason, my has_many through association isn't working. Here are my models:
class Interest < ActiveRecord::Base
has_many :evints
has_many :events, through: :evints
has_many :images, through: :events
end
class Event < ActiveRecord::Base
has_many :evints
has_many :images
has_many :interests, through: :evints
end
class Evint < ActiveRecord::Base
belongs_to :events
belongs_to :interests
end
The Evints table has three columns: interest_id, event_id, and id.
When I call #interest.events, I get the error message
uninitialized constant Interest::Events
Obviously, there's something going wrong with the association if #interest.events is being read as a constant!
Does anyone have any ideas?
Thanks!
Check your Evint class, it should be:
class Evint < ActiveRecord::Base
belongs_to :event
belongs_to :interest
end
On a different note, I think Evint isn't really a very good name. It'd suggest that you go with EventInterest, and name the table event_interests.
What I want to do is to get all the
My model:
class User < ActiveRecord::Base
has_many :classes
has_many :professors, :through=>:classes
has_many :cars
has_many :carmodels, :through=>:cars
end
class Professor < ActiveRecord::Base
has_many :classes
has_many :users, :through=>:classes
end
class Class < ActiveRecord::Base
belongs_to :user
belongs_to: professor
end
class Car < ActiveRecord::Base
belongs_to :user
belongs_to :carmodel
end
class Carmodel
has_many :cars
has_many :users, through=>:cars
end
what I want to do is, given a certain Car and Professor, to find all users which contain them.
for example
u1=carmodel.users
u2=professor.users
result=[]
u1.each do |us|
if u2.include? us
result.push us
end
end
Of course this is just an example... I would like to keep working with ActiveRecords(avoid turning it to an array) and, of course, a more optimal solution... I can't seem to find any.
You need to do something like this:
User.joins(:carmodels).joins(:professors)
Thanks for the previous answer! Here is the resulting code:
carmodel #Variable for the wanted carmodel
professor #Variable for the wanted professor
result=User.joins(:carmodels).joins(:professors).where(carmodel:{id:carmodel.id},professors:{id:professor.id})
Thanks again!