I have tried everything i thought would work for this and am turning up nothing.
in rails 3, I need to find all users with a cd player in their car. A car has one user and one radio, and a user belongs to a car, and a radio has many cars.
I am stumbling on how I would perform this search via a scope in the user model.
class User
belongs_to :car
class Car
belongs_to radio
has_one :user, :dependent => destroy
class Radio
has_many :cars
I am assuming that you mean this:
Car has radio_id, User has car_id,
since a radio has many cars and car has one user. The table with the foreign key always is on the belongs_to end of the relationship.
Without really knowing the structure you're looking for, something like the following should work:
scope :with_cd_player, joins(:cars).where('cars.radio_id is not null')
if there is a category column on the radio, the following would work.
scope :with_cd_player, joins(:car => :radio).where('cars.radio_id is not null').where("radios.category = 'cd_player'")
For Rails Version >= 4:
scope :with_cd_player, -> { joins(:cars).where.not(cars: { radio_id: nil }) }
Also you can using "merge"
https://gorails.com/blog/activerecord-merge
Related
class User
has_one :settings
class Settings
belongs_to :user
I want to do something like
#user_with_no_settings = User.where(:settings => nil)
But this returns an empty relation.
How do I find all users which don't have a settings related to them? (So I will find them and create them)
Most importantly, your association is incorrect;
Change it to:
class User
has_one :setting
class Settings
belongs_to :user
The Class name is plural but the association has_one is always singular. So you can't use :settings for has_one as oppose to has_many which is always plural.
Use this:
User.where("id not in (select user_id from settings)")
The above query will give all the users which don't have a settings associated to them.
Okay. In your situation you may need some TRY this code.
User.where('id NOT IN (?)', User.joins(:settings).pluck('settings.user_id'))
But, you need to follow Rails Convention.
Change settings to setting.
I am working with a Rails polymorphic inheritance configuration - I have the following setup:
User < ActiveRecord::Base
belongs_to :rolable, :polymorphic => true
Student < ActiveRecord::Base
has_one :user, :as => :rolable
accepts_nested_attributes_for :user
Teacher < ActiveRecord::Base
has_one :user, :as => :rolable
accepts_nested_attributes_for :user
I want to be able to capture email address for teachers and a username for students (who won't typically have an email address). I defined those as attributes of the User model, but now I'm stuck when I try to do validations for Student and Teacher. I didn't define them in their respective models because I'm using Devise and there will be other user types. Abstracting what is currently type to a Role pattern isn't a good fit for my particular scenario either.
Since username and email are properties of User what I basically want to do is check if the rolable_type field from the polymorphic relationship is type student and if so, make username required and email not, but in the new method that property isn't set. However Rails 'knows' this is a Student, so it feels like there's some way to check the instance type. The closest link I've found to what I'm shooting for is the third comment to the accepted answer in this question: How to apply different validation rule according to polymorphic association type (Rails)?, but I'm having trouble getting the method_missing syntax correct as I'm not experienced with metaprogramming. Am I on the right track with this? Or is there a simpler way? Or should I move the properties to the polymorphic models instead?
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 am new to Rails and finished Michael Hartl's "Ruby on Rails 3 Tutorial". Although the book teaches me a lot, I find this puzzle I don't understand.
To preview the puzzle, that is, I don't understand, inside User model,
has_many :following, :through=>:relationship, :source=>:followed
how this piece of code link "user.following" to an array of User instances.
And below is the whole puzzle.
First of all, I have the Relationship model, which records followed_id and follower_id infos. Inside Relationship model, the association is simple as
class Relationship < ActiveRecord::Base
attr_accessible :followed_id
belongs_to :follower, :class_name => "User"
belongs_to :followed, :class_name => "User"
end
Then, inside the User model, a user will assume the role of follower, and collect all its following rows in relationships table through relationships association.
class User < ActiveRecord::Base
.
.
.
has_many :relationships, :foreign_key => "follower_id", :dependent => :destroy
.
Until now, I got it.
But confusion came at the next line, where through user.following it can assemble all that user's following(User instances). Like so,
has_many :following, :through=>:relationships, :source=>:followed
I understand that :source=>:followed will overwrite the default, and let find all followed_ids associated with that user.
But, how can Rails recognize followed_id to link to User object? The label name doesn't match users, nor is there :class_name specified. I just don't get how Rails do this underlying work, or I missed out some hints.
Thank you! :)
But, how can Rails recognize followed_id to link to User object? The
label name doesn't match users, nor is there :class_name specified. I
just don't get how Rails do this underlying work, or I missed out some
hints.
Rails recognize that is an user object because it is set in Relationship's belongs_to. What Rails does here is to follow the relationship class through the foreign key "follower_id" and returning every User that has a relationship with the current user as followed. Of course Rails do that in a single SQL statement like this:
SELECT `users`.* FROM `users` INNER JOIN `relationships` ON `relationships`.followed_id = `users`.id WHERE ((`relationships`.follower_id = <the current user id> ))
has_many :following, :through=>:relationships, :source=>:followed
This explains to Rails that following is the inverse relationship of following and that users has many following and followed through his relationships.
The way Rails knows that followed_id is linked to User is that it is defined in your Relationship model.
Hope you've understood ! Good luck :)
For example, one user has joined many group; and one group has many user members. Now I get a user object and a group object, I want to know whether this user is a member of this group.
I can see some methods, but still wandering whether there is a better way?
So, if i understand your question, what you have is something like:
class User < ActiveRecord::Base
has_many :groups, :though => :user_members
class Group < ActiveRecord::Base
has_many :users, :though => :user_members
And you want to know if a user is a member of a specific group.
So, given something like:
u = User.first
g = Group.first
Just do:
u.groups.include? g
Thats all there is to it!
ian.
ipd's way is fine, another more Rails oriented way to do it is :
u.groups.exists?(g)