polymorphic-associations

问题 OK, this is an interesting and most importably real urgent problem for me to solve... In order for others to neatly comprehend it, I've stretched myself to make a well illustrated post. The Object Model So I have this simple, easy and "beautiful" model in mind. See the first picture. (You can ignore PathEntry , it's not relevant in my situation.) The idea is that a MediaFeedItem owns: a collection of ThumbnailFileEntries (accesible through the ThumbnailFiles property) at most 1 raw FileEntry

问题 OK, this is an interesting and most importably real urgent problem for me to solve... In order for others to neatly comprehend it, I've stretched myself to make a well illustrated post. The Object Model So I have this simple, easy and "beautiful" model in mind. See the first picture. (You can ignore PathEntry , it's not relevant in my situation.) The idea is that a MediaFeedItem owns: a collection of ThumbnailFileEntries (accesible through the ThumbnailFiles property) at most 1 raw FileEntry

问题 I'm wondering if this its even posible. I want to join 2 tables based on the data of table 1. Example table 1 has column food with its data beeing "hotdog". And I have a table called hotdog. IS it possible to do a JOIN like. SELECT * FROM table1 t join t.food on id = foodid I know it doesnt work but, its even posible, is there a work arround?. Thanks in advance. 回答1: No, you can't join to a different table per row in table1 , not even with dynamic SQL as @Cade Roux suggests. You could join to

问题 I'm slightly confused about a polymorphic association I've got. I need an Article model to have a header image, and many images, but I want to have a single Image model. To make matters even more confusing, the Image model is polymorphic (to allow other resources to have many images). I'm using this association in my Article model: class Article < ActiveRecord::Base has_one :header_image, :as => :imageable has_many :images, :as => :imageable end Is this possible? Thanks. 回答1: Yep. That's

问题 I am trying to make an app in Rails 4. I have a profile model and an address model. the Associations are: profile.rb has_many :addresses, as: :addressable address.rb belongs_to :addressable, :polymorphic => true Address is a polymorphic model. I have an address form which has: <%= simple_form_for(@address) do |f| %> <%= f.error_notification %> <div class="form-inputs"> <div class="row"> <div class="col-xs-3"> <%= f.input :unit %> </div> <div class="col-xs-3 col-xs-offset-1"> <%= f.input

问题 I am trying to roll together two Railscasts: http://railscasts.com/episodes/262-trees-with-ancestry and http://railscasts.com/episodes/154-polymorphic-association on my app. My Models: class Location < ActiveRecord::Base has_many :comments, :as => :commentable, :dependent => :destroy end class Comment < ActiveRecord::Base belongs_to :commentable, :polymorphic => true end My Controllers: class LocationsController < ApplicationController def show @location = Location.find(params[:id]) @comments

问题 So I'm looking at someone's code which has the following (paraphrased): class user has_one :connection, :dependent => :destroy has_one :second_user, :through => :connection, :class_name => 'User' end class connection belongs_to :user belongs_to :second_user, :class => 'User' end If I have a connection object and delete the associated 'user' it can be destroyed fine. But I also want to make it so that if the User occupying the 'second_user' field is destroyed the connection is destroyed. How

问题 I'm trying to figure out how to implement an evaluation model in my Rails 4 app. I've previously asked these related questions but am yet to solve this problem: Rails 4 Polymorphic associations and concerns Rails 4 - post completion evaluations model - structure I have: class Evaluation < ActiveRecord::Base belongs_to :evaluator, :polymorphic => true belongs_to :evaluatable, :polymorphic => true I have also made concerns for evaluator and evaluatable as: module Evaluator extend ActiveSupport:

问题 I have an attachments table that has multiple values (via polymorphic assoc). I'd like to be able to search for multiple values (like an AND in SQL) via thinking-sphinx. For example: class FieldValue < ActiveRecord::Base belongs_to :customized, :polymorphic => true end class Attachment < ActiveRecord::Base has_many :field_values, :as => :customized, :dependent => :destroy define_index do has field_values.field_id, :as => :field_ids, :type => :multi indexes field_values.value, :as => :field

问题 I would like to be able to call the build method on a scope that targets a certain class of model via its STI type, and have ActiveRecord build an instance of the correct class. class LineItem < ActiveRecord::Base scope :discount, where(type: 'DiscountLineItem') end class DiscountLineItem < LineItem; end > LineItem.discount.build # Expect an instance of DiscountLineItem here => #<LineItem ...> Here, I expected an instance of DiscountLineItem , not an instance of LineItem . 回答1: Even though