Caution: I am a 4 week old at programming. I am having trouble with a has_many :through => relationship between my Neighborhood and Cta_train models.
Here are my models:
class CtaTrain < ActiveRecord::Base
belongs_to :Ctaline
has_and_belongs_to_many :searches
has_many :neighborhoods, :through => :CtaLocation, :foreign_key => :neighborhood_id
has_many :CtaLocations
end
class Neighborhood < ActiveRecord::Base
has_many :geopoints
has_many :listings
has_many :properties
has_and_belongs_to_many :searches
has_many :CtaTrains, :through => :CtaLocation, :foreign_key => :cta_train_id
has_many :CtaLocations
end
class CtaLocation < ActiveRecord::Base
belongs_to :neighborhood
belongs_to :CtaTrain
end
When I try to do this:
neighborhood.CtaTrains
I get this error:
ActiveRecord::HasManyThroughAssociationNotFoundError (Could not find the association :CtaLocation in model Neighborhood):
I have been slogging through this for several hours now....I have tried many iterations of ideas from stackoverflow....what I show above feels like the closest solution, but obviously still not working. Any thoughts would be appreciated!
I think the problem is that you're not following Rails conventions by using lowercase/underscore for your symbols. Class names have to be CamelCase but you should be doing the following everywhere else:
class CtaTrain < ActiveRecord::Base
belongs_to :cta_line
has_and_belongs_to_many :searches
has_many :neighborhoods, :through => :cta_locations, :foreign_key => :neighborhood_id
has_many :cta_locations
end
*Update: You should also be using :cta_locations (plural) in your has many through
Related
I've got a Person who can be linked to many Structures (structure is polymorphic)
I've got a Venue, who can have many People, as a structure.
I've got a Journal, who can have many People, as a structure.
Here is my modelization :
class Venue < ActiveRecord::Base
has_many :structure_people, :as => :structure
has_many :people, :through => :structure_people
end
class Journal < ActiveRecord::Base
has_many :structure_people, :as => :structure
has_many :people, :through => :structure_people
end
class Person < ActiveRecord::Base
has_many :structure_people
has_many :structures, :through => :structure_people
end
class StructurePerson < ActiveRecord::Base
belongs_to :structure, polymorphic: true
belongs_to :person
end
My problem :
when i try to get people on a Venue or on a Journal, it works. Cool :)
BUT
when i try to get structures on a person, i've got an error :
ActiveRecord::HasManyThroughAssociationPolymorphicSourceError: Cannot have a has_many :through association 'Person#structures' on the polymorphic object 'Structure#structure'.
Anyone could help me to solve this ?
Thanks a lot.
Christophe
I think it's a restriction of Rails, because has_many association will guess a class_name automatically. But polymorphic association may returns multiple class_name. Do you mind use this:
class Person < ActiveRecord::Base
has_many :structure_people
has_many :venues, :through => :structure_people
#Journal is the same.
end
class StructurePerson < ActiveRecord::Base
belongs_to :structure, polymorphic: true
belongs_to :venue, :foreign_key => 'structure_id', :conditions => {:structure_type => 'Venue'}
belongs_to :person
end
Although it is an ugly solution...
I think you can choose an alternative way.
class Person < ActiveRecord::Base
has_many :structure_people
def structures
structure_people.map(&:structure)
end
end
You can't get chaining function of has_many, but you can get polymorphic structures :)
I have the following models:
class User < ActiveRecord::Base
has_many :groups, :through => :memberships
has_many :memberships, :class_name => "User::Group"
end
class Group < ActiveRecord::Base
has_many :users, :through => :members
has_many :members, :class_name => "User::Group"
end
class User::Group < ActiveRecord::Base
belongs_to :user
belongs_to :group
end
I make the following association call:
#user.groups
And it returns an array of User::Groups, instead. Am I overlooking something?
I changed the name of the join table to User::Membership, and now everything works as expected. It seems that naming the last part of the namespace after another model was causing some sort of interference, though I'm not sure why. Does anyone have a more informed explanation?
Imagine 4 models in Rails 3.1
class Student < ActiveRecord::Base
has_many :memberships
has_many :courses, :through => :memberships
has_many :tests, :through => :courses
end
class Membership < ActiveRecord::Base
belongs_to :student
belongs_to :course
end
class Course < ActiveRecod::Base
has_many :tests
has_many :students, :through => :memberships
end
class Test < ActiveRecord::Base
belongs_to :course
end
How can I output a sorted list (ie by date) of a student's upcoming tests
(I'm guessing there is a fairly simple answer, but I've been trying in vain for a while)
My best guess is something like:
#upcomingTests = #currstudent.tests.sort_by &:testDateTime
but it seems to return an empty array
First of all, there is an slight error on your model "Course". It needs "belongs_to :student".
class Course < ActiveRecod::Base
has_many :tests
has_many :students, :through => :memberships
belongs_to :student
end
After you've created and populated a foreign key, you can create a simple named_scope on your test mode:
named_scope :ordered, :order => "created_at DESC"
Then it's just the matter of accessing it from wherever you want:
#ordered_tests = #student.tests.ordered
What if I had 3 Models that I wanted to connect.
For example:
A user can have many different permissions for many different applications.
So I need a table to store:
user_id
permission_id
application_id
Is that possible with has_and_belongs_to_many?
Thanks
I would do it with a has_many :through.
class Upa < ActiveRecord::Base
belongs_to :user
belongs_to :permission
belongs_to :application
end
class User < ActiveRecord::Base
has_many :permissions, :through => :upas
has_many :applications, :through => :upas
end
class Permission < ActiveRecord::Base
has_many :users, :through => :upas
has_many :applications, :through => :upas
end
class Application < ActiveRecord::Base
has_many :permissions, :through => :upas
has_many :users, :through => :upas
end
examples of has_many :through
Basically any sort of relationship that you can describe with a classical one to one, one to many and many to many relationships in relational databases can be described in ActiveRecord.
Yes, you can have has_and_belongs_to_many relationship. More help can be found here http://api.rubyonrails.org/classes/ActiveRecord/Associations/ClassMethods.html
I am having some trouble creating a nested association and I can't quite spot what's going on:
class Package < ActiveRecord::Base
has_many :selections, :class_name => "PackageSelection"
has_many :channels, :through => :selections
has_many :categories, :through => :channels, :source => ?????
end
class Channel < ActiveRecord::Base
belongs_to :category
has_many :package_selections
has_many :packages, :through => :package_selections
end
class Category < ActiveRecord::Base
has_many :channels
end
I am trying to figure out how to build the association to categories. Any advice?
It seems like this is impossible in Rails Core (currently 2.3) but someone has written a plugin to allow it