I have two models App and Contact. App has a has_one relationship with Contact. I have declared the accepts_nested_attributes_for clause in the App model for Contact. Now, in the apps_controller, if I use the build method on the app object, I get an error for the the nil class, even though I had declared the relationship.
App.rb
class App < ActiveRecord::Base
has_one :contact_person, :dependent => :destroy
accepts_nested_attributes_for :contact_person
end
ContactPerson.rb
class ContactPerson < ActiveRecord::Base
belongs_to :app
end
apps_controller.rb
def new
#app = App.new
#app.contact_person.build
end
Could you please point me out whether am I doing anything incorrectly. I have used nested models before but have not encountered this error.
I am supposed to use #app.build_contact_person instead of #app.contact_person.build. In this way, it worked :)
Declaring association does not automatically creates it:
class App < ActiveRecord::Base
has_one :contact_person, :dependent => :destroy
accepts_nested_attributes_for :contact_person
# Adding this line should work
after_create { self.contact_person = ContactPerson.new }
end
Related
I have three models defined as follows
class Student < ActiveRecord::Base
belongs_to :user
has_many :placements
has_many :companys , through: :placements
end
class Company < ActiveRecord::Base
has_many :placements
has_many :students , through: :placements
end
class Placement < ActiveRecord::Base
belongs_to :student
belongs_to :company
before_save :set_placed
def set_placed
s = self.student
s.is_placed = true
s.save
end
end
Each time i add data for placement object i want to update a field in its corresponding student object. But when i use rails_admin to add data , i am getting the error Placement failed to be created .
When i remove the before_save call , data can be added.
I am using better_errors gem for debugging. I am getting the following from it
#_already_called
{[:autosave_associated_records_for_student, :student]=>false,
[:autosave_associated_records_for_company, :company]=>false}
i am hoping this could be the reason for error.
How can i solve this error??
You have a s.save in your set_placed callback. You don't save an ActiveRecord object in a callback, and especially not in a before_save callback.
try this,
def set_placed
self.student.is_placed = true
end
I need to pass updated paramaters to back to a parent model when saving a series of its children.
For example if a save a bunch of employees to each task through a project, I need to let the project know the title of some of its tasks have changed, then I need to collect all the titles that changed and process them in the ProjectObserver. Is this possible?
I realize there might not be a way to make this work the way I'm trying. If not I'm happy to hear suggestions about how I might be able to get around this.
Here is what I have tried without any success:
class Employee < ActiveRecord::Base
has_many :employee_tasks
has_many :tasks, :through => :employee_tasks
accepts_nested_attributes_For :employee_tasks
accepts_nested_attributes_For :tasks
end
class Project < ActiveRecord::Base
attr_accessor :changed_employees
has_many :tasks
end
class Task < ActiveRecord::Base
has_many :employee_tasks
has_many :employees, :through => :employee_tasks
belongs_to :project
accepts_nested_attributes_For :employee_tasks
end
class EmployeeTask < ActiveRecord::Base
#this is what I want to accomplish
before_save do
if self.employee_id_changed
self.task.project.changed_employees ||= []
self.task.project.changed_employees << self.employee_id_changed
end
end
belongs_to :task
belongs_to :employee
end
class ProjectObserver < ActiveRecord::Observer
observe :project
def after_save(project)
puts project.changed_employees
# should print out the changed attributes loaded from EmployeeTask
#send a single email with all the updated titles (not one email for each change)
end
end
Sounds like you need to use the after_save method described here http://api.rubyonrails.org/classes/ActiveRecord/Callbacks.html
I'm using single table inheritance in my application and running into problems building inherited users from an ancestor. For instance, with the following setup:
class School < ActiveRecord::Base
has_many :users
end
class User < ActiveRecord::Base
attr_accessible :type #etc...
belongs_to :school
end
Class Instructor < User
attr_accessible :terms_of_service
validates :terms_of_service, :acceptance => true
end
Class Student < User
end
How can I build either a instructor or student record from an instance of School? Attempting something like School.first.instructors.build(....) gives me a new User instance only and I won't have access to instructor specific fields such as terms_of_service causing errors later down the rode when generating instructor-specific forms, building from console will give me an mass-assignment error (as it's trying to create a User record rather than an Instructor record as specified). I gave the example of School, but there are a few other associations that I would like to inherit from the User table so I don't have to repeat code or fields in the database. Am I having this problem because associations can not be shared in an STI setup?
You should specify instructors explicitly
class School < ActiveRecord::Base
has_many :users
has_many :instructors,:class_name => 'Instructor', :foreign_key => 'user_id'
end
And what else:
class School < ActiveRecord::Base
has_many :users
has_many :instructors
end
class Instructor < User
attr_accessible :terms_of_service # let it be at the first place. :)
validates :terms_of_service, :acceptance => true
end
OK it seems part of the problem stemmed from having the old users association inside of my School model. Removing that and adding the associations for students and instructors individually worked.
Updated School.rb:
class School < ActiveRecord::Base
#removed:
#has_many :users this line was causing problems
#added
has_many :instructors
has_many :students
end
I just can't figure out how to create a relation with a join table. I've read all the posts about them, but the main error seems to be that in the join table to models should be singular, which I have. I just can seem to create the models correctly and assign them. I have projects with datasets, and projects can have multiple datasets, while a dataset can belong to multiple projects. A dataset can be active or not, which is why I need the has_many through instead of the has_many_and_belongs_to setup.
My model definitions are:
class Project < ActiveRecord::Base
attr_accessible :name, :user_id
belongs_to :user
has_many :activedatasets
has_many :datasets, :through => :activedatasets
end
class DataSet < ActiveRecord::Base
attr_accessible :name, :project_id, :filename, :tempfilename
has_many :activedatasets
has_many :projects, :through => :activedatasets
end
class ActiveDataSet < ActiveRecord::Base
attr_accessible :active, :data_set_id, :project_id
belongs_to :project
belongs_to :dataset
end
When I create a new dataset I've got the project_id in the params, so I'm trying to setup the relationship like below:
class DataSetsController < ApplicationController
def new
#dataset = DataSet.new
#dataset.activedatasets.project_id = params[:project_id]
end
end
The error I'm getting seems famous:
NameError in DataSetsController#new
uninitialized constant DataSet::Activedataset
Can anybody point me in the right direction please?
Thanks for you attention.
You need to use:
has_many :active_data_sets
has_many :data_sets, :through => :active_data_sets
And in the DataSet model:
has_many :active_data_sets
has_many :projects, :through => :active_data_sets
Basically, rails expects you to use underscores to separate words in association names, and converts them to CamelCase. So active_data_sets becomes ActiveDataSet. Rails then uses this to work out which model class the association is with.
You also need to change your controller to this:
class DataSetsController < ApplicationController
def new
#dataset = DataSet.new
#dataset.active_data_sets.build(:project_id => params[:project_id])
end
end
Otherwise you'll get an error because you tried to set the project_id of the active_data_sets collection rather than creating a new ActiveDataSet.
How can I delete nested objects in a form? I found out that I need to add :allow_destroy in the parent model at the accepts_nested_attributes_for directive.
Further, I want to restrict the deletion. A nested object only should be deleted, if the parent object is the only one that retains the association.
Example:
class Internship < ActiveRecord::Base
belongs_to :company
accepts_nested_attributes_for :company, allow_destroy => true
end
class Company < ActiveRecord::Base
has_many :internships
end
Explanation: A company can host many internships. Therefore, I do not want to delete the company record as long as there is at least one other internship associated with it.
You could use dependent => :destroy
class Internship < ActiveRecord::Base
belongs_to :company
accepts_nested_attributes_for :company, allow_destroy => true
end
class Company < ActiveRecord::Base
has_many :internships, :dependent => :destroy
end
If you return false in a before_destroy filter, then the destroy action will be blocked. So we can check to see if there are any internships associated to the company, and block it if so. This is done in the company model.
class Company < ActiveRecord::Base
has_many :internships
before_destroy :ensure_no_internships
private
def ensure_no_internships
return false if self.internships.count > 0
end
end