In my project I have 3 models Assignment, Question and MultipleChoice with the following associations
assignment.rb
has_many :questions, dependent: :destroy
question.rb
belongs_to :assignment, class_name: 'Assignment', foreign_key: :assignment_id
has_many :multiple_choices, dependent: :destroy
multiple_choice.rb
belongs_to :question
Now I want to make a query like below
#assignment = Assignment.find(params[:id])
#questions = #assignment.questions.includes(:multiple_choices)
This is not working as expected.
So, I want all questions that belongs to the assignment for the params[:id] and the associated multiple choices that belongs to a question. My above query do not give any error but it only show questions not multiple choices associated with question. How can I do this? I am learning api development for rails. So I want to send this value as json and probably I will need serialization. How can I do this? I am working on rails 4.
Edit
well the output for
#questions = #assignment.questions.includes(:multiple_choices) and
#questions = #assignment.questions.eager_load(:multiple_choices) and
#questions = #assignment.questions are all same.
I dont understand why the output do not include any value from multiple choices table
Output of the command
#assignment.questions.eager_load(:multiple_choices).to_sql id
=> "SELECT \"questions\".\"id\" AS t0_r0, \"questions\".\"content\" AS t0_r1, \"questions\".\"q_type\" AS t0_r2, \"quest
ions\".\"created_at\" AS t0_r3, \"questions\".\"updated_at\" AS t0_r4, \"questions\".\"assignment_id\" AS t0_r5, \"multi
ple_choices\".\"id\" AS t1_r0, \"multiple_choices\".\"content\" AS t1_r1, \"multiple_choices\".\"created_at\" AS t1_r2,
\"multiple_choices\".\"updated_at\" AS t1_r3, \"multiple_choices\".\"question_id\" AS t1_r4 FROM \"questions\" LEFT OUTE
R JOIN \"multiple_choices\" ON \"multiple_choices\".\"question_id\" = \"questions\".\"id\" WHERE \"questions\".\"assignm
ent_id\" = $1"
The behaviour for includes function changed in Rails 4. You can find more details here:
http://blog.arkency.com/2013/12/rails4-preloading/
I also suppose, that if you will use eager_load instead of includes, you will get the result you need.
#assignment is an object from which you are getting the questions.
But with #questions = #assignment.questions.includes(:multiple_choices) how can you get the multiple_choices without calling this on an object?
Try this->
#assignment = Assignment.includes(:questions).find(params[:id])
#assignment.questions.includes(:multiple_choices).collect {|question| question.multiple_choices }
This also includes eager loading.
Hope you'll get what you expect.
Related
I'm at my wit's end. I upgraded to Rails 4.2.10, and everything is terrible.
Here is the relevant part of /models/product.rb
class Product < ActiveRecord::Base
delegate_attributes :price, :is_master, :to => :master
And here is /models/variant.rb:
class Variant < ActiveRecord::Base
belongs_to :product
The variants table has fields for "price" and "is_master". Products table does not.
It used to be the case that one could access Product.price and it would get/set the price for the master variant (there's really only one variant per product, the way things are currently set up).
Now it complains that:
NoMethodError: undefined method `price=' for #<Product:0x0000000d63b980>
It's true. There's no method called price=. But why wasn't this an issue before, and what on earth should I put in that method if I create it?
Here's the code to generate a product in db/seeds.rb:
product = Product.create!({
name: "Product_#{i}",
description: Faker::Lorem.sentence,
store_id: u.store.id,
master_attributes: {
listing_folder_id: uuids[i],
version_folder_id: uuids[i]
}
})
product.price = 10
product.save!
end
delegate_attributes isn't a Rails method and looks like it comes from a gem (or gems) that aren't actively maintained?
If there's a new version of whatever gem you're using that might help, because the short answer is that part of the "delegating" of an attribute would involve getting and setting the attribute, so it would generate #price= for you.
If you want to define it yourself, this should do it (within your Product class):
def price=(*args)
master.price=(*args)
end
or if you want to be more explicit:
def price=(amount)
master.price = amount
end
Short version: I'm building a new Rails 4 application that uses (read-only) some tables from a database used by a legacy Rails 2 application, which is still in use. The old application models/tables were very confusingly named, however (especially in the context of the new application), so I want to use different names for the models/tables using self.table_name. This all works perfectly until I tried to add in a polymorphic relationship. Rails ignores my defined table_name and does a query on the type using the new model name, which of course is different so it doesn't work. Is there any way to change this?
Long version: There are three models in this equation, and here they are:
class Exporter < MysqlBase
has_many :lic_exporter_addresses, :as => :place
self.table_name = 'excons'
self.primary_key = 'id'
end
class LicBusiness < MysqlBase
has_one :physical_address, -> { where(category: 'Physical') }, :class_name => 'LicExporterAddress', :as => :place
has_one :mailing_address, -> { where(category: 'Mailing') }, :class_name => 'LicExporterAddress', :as => :place
has_many :lic_exporter_addresses, :as => :place
self.table_name = 'businesses'
self.primary_key = 'id'
end
class LicExporterAddress < MysqlBase
belongs_to :place, polymorphic: true
self.table_name = 'addresses'
self.primary_key = 'id'
end
We have a ton of different kinds of businesses, so the Business model is the most problematic. I really don't want to have that in the new app because it would be very confusing as to what a "business" actually is. With the current code if I go into the rails console and try to get lic_exporter_addresses for a LicBusiness or Exporter, it does:
SELECT `addresses`.* FROM `addresses` WHERE `addresses`.`place_id` = '00044c693f6848f9b0978f873cf9999a' AND `addresses`.`place_type` = 'LicBusiness'
when what I need is place_type = 'Business'.
Is there any way to tell Rails what place_type to look for? I did see this question and the second answer looked promising, except that I'm already sort of doing that with Physical and Mailing addresses so I can't figure out how that'd work with both options at the same time... Thanks for any info or ideas.
In Rails 4.2, it looks like the exact string used for the query is defined as owner.class.base_class.name, where owner is the model declaring the association. So I don't think it's directly supported. But there are a few ways I can think of to hack around this. I think the most promising might be, in LicBusiness:
has_many :lic_exporter_addresses, ->{where place_type: "Business"}, foreign_key: "place_id"
That is, don't define the association as polymorphic, but define the type scope yourself. This will NOT correctly define place_type in the lic_exporter_addresses table if you ever use lic_exporter_address.place = some_lic_business_instance. However you said this table was read-only, so this may in fact not be an issue for you. If it is, there may be ways to override the behavior to get what you need.
Two other ideas both make me very nervous and I think they are probably quite dangerous for unintended side-effects. They are to override LicBusiness.base_class (this might actually be ok if you do not now and never will have STI set up on LicBusiness, but I'm still nervous), or to override LicBusiness.name (I'm pretty sure this would have unintended side-effects).
I have two models, Question and Answer.
class Answer < ActiveRecord::Base
belongs_to :question
end
class Question < ActiveRecord::Base
has_many :answers
end
In my controller action, what I want to do is to determine all of the questions that a user has answered. I have a query that finds all of the answers for a user:
#answers = current_user.answers
Now, I want to find out what Questions those relate to. I tried
#questions = Question.where("id in ?", #answers)
but it doesn't work. I get this error:
Mysql2::Error: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '4,5,6)' at line 1: SELECT `questions`.* FROM `questions` WHERE (id in 4,5,6)
When I try this:
#questions = Question.where("id in ?", #answers.question_id)
I get this error (question_id is a field in Answer):
undefined method `question_id' for [4, 5, 6]:Array
How can I best query Questions based on Answers a User has?
Question.where(id： #answers.map(&:question_id))
You can approach the problem from a different angle. You could have a custom scope in your Question model:
scope :by_answerer, -> (user_id) { includes(:answers).where(answers: {user_id: user_id}) }
Then in your User model:
def answered_questions
Question.by_answerer(id)
end
The clue is in the SQL that is generated (in the error message)
SELECT `questions`.* FROM `questions` WHERE (id in 4,5,6)
that's not valid syntax. You want
SELECT `questions`.* FROM `questions` WHERE (id in (4,5,6))
so you're looking for
#questions = Question.where("id in (?)", #answers)
I really can't get my head around Rails 4 strong parameters, belongs_to association and form with fields_for.
Imagine I have model for quoting some price:
class Quote < ActiveRecord::Base
belongs_to :fee
accepts_nested_attributes_for :fee
Now, I have seeded some fees into the db, and have put some radiobuttons on my form_for #quote using fields_for. The values of the radiobuttons are simply ids of the records.
Here is the troubling part, the controller:
def create
#quote = Quote.new(quote_params)
...
end
def quote_params
params.require(:quote).permit(:amount_from, fee_attributes: [:id])
end
From my understanding, automagically Rails should fetch fee record with some id, but there is some mystic error instead.
params hash is: "quote"=>{"amount_from"=>"1200", "fee_attributes"=>{"id"=>"1"}}
Log tail:
Completed 404 Not Found in 264ms
ActiveRecord::RecordNotFound (Couldn't find Fee with ID=1 for Quote with ID=)
app/controllers/quotes_controller.rb:14:in `create'
I really don't understand what is going on here, have read Rails association guide, googled for hour for all info, but to no avail.
What I want to achieve here is to understand the correct "Rails way" to fetch some associations for new Quote object using some params I've put in the form.
Guess I got nested_attributes_for wrong, somehow thought it would call Fee.find automagically.
I've opted for ditching fields_for helpers from the form and rendering fields manually like
radio_button_tag 'fee[id]', fee.id
Then in controller I have 2 params methods now:
def quote_params
params.require(:quote).permit(:amount_from)
end
def fee_params
params.require(:fee).permit(:id)
end
And my action looks like
def create
#quote = Quote.new(quote_params)
#quote.fee = Fee.find(fee_params[:id])
...
Any additions on best practices when one has to handle lots of different objects with not so straight init logic are welcome.
I am quite new to Rails so this question might be a bit weird... I am building a system where I want Users to be able to leave Feedback regarding the other Users, but also regarding the Item they bought from them. Think of eBay feedback where they ask: Were you pleased with the item? and Would you recommend working with Joe?
Feedback model is obviously polymorphic since it can be of type User or Item
What I have is:
class User
has_many :feedbacks, as: :feedbackable
end
class Item
has_many :feedbacks, as: :feedbackable
end
class Feedback
belongs_to :feedbackable, polymorphic: true
end
The problem I have with this is that Users are creators of the Feedback, but also the receivers (feedbackable) of the same feedback...
How do I achieve something like this:
class User
has_many :feedbacks # feedback.user
has_many :feedbacks, as: :feedbackable #feedback.feedbackable.type_id
end
In the sense that I can get all feedbacks that user A has left to other users and items and also all feedbacks that other users has left about the user A
I am not sure about the politics of answering my own question, but I'll leave this answer here for anyone dealing with the same doubt...
For those of you who started reading about STI or many-to-many :through etc. it seems it's much easier to achieve this.
I ended up doing the following in the User model:
has_many :feedbacks
has_many :feedbacks_received, as: :feedbackable, :class_name => "Feedback"
Now I can do:
user.feedbacks and get all feedbacks that this user created (on Item or User)
and
user.feedbacks_received and get all feedbacks other users left about this user