single-table-inheritance

问题 I have an ActiveRecord class called 'DynObject' which can be used for inheritance.. On initialization I dynamically create some Classes that inherit from it: classes_config = { foo: 'foo', bar: 'bar' } classes_config.each do |name,options| klass = Class.new( DynObject ) do end self.klasses[name] = const_set( "#{name.camelize}DynObject", klass ) end This is all good, these classes are created just fine.. But when ActiveRecord tries to load created records the STI mechanism failes..

问题 I get a lot of mapping errors in Symfony's profiler. I only have this problem with associations with the table inheritance super class. All the other entities and relations are just fine and working perfectly. Errors: ***\ArticleBundle\Entity\Article The mappings ***\ArticleBundle\Entity\Article#buyer and ***\UserBundle\Entity\User#boughtArticles are inconsistent with each other. The association ***\ArticleBundle\Entity\Article#category refers to the inverse side field ***\ArticleBundle

问题 I have the following models: class Test < ApplicationRecord end class Exam < Test end class Practice < Test has_many :relations has_many :questions, through: :relations end class Relation < ApplicationRecord belongs_to :practice belongs_to :question end class Question < ApplicationRecord has_many :relations has_many :practices, through: :relations end And this is my schema: create_table "questions", force: :cascade do |t| t.string "title" t.text "text" t.datetime "created_at", null: false t

问题 When defining a relationship, there is a property on the related model (not a DB column), but I would like to sort by it (in the @OrderBy annotation). I have a base model that is extended using single table inheritance. The property in question is basically an order property that is specified in each child class, but is not saved to the DB. (I don't want to add an order column to the DB table, since the ordering depends purely on which child class the discriminator is mapped to. There is

问题 These are the options I see that can help solve "Rails 5 - Object Relation Impedence and how to structure multiple inherited classes/tables" TL;DR - the Object Table Impedance ORM problem. Abstract base class, with each child class having its own table (ie storing the common attributes for each type in its own table) STI, just put everything in one Base class and Table, and create all child attributes in that table, but have the sub-classes (ie your other Rails models) inherit from that Base

问题 I have a Card model that has many CardSets and a CardSet model that has many Cards through a Membership model: class Card < ActiveRecord::Base has_many :memberships has_many :card_sets, :through => :memberships end class Membership < ActiveRecord::Base belongs_to :card belongs_to :card_set validates_uniqueness_of :card_id, :scope => :card_set_id end class CardSet < ActiveRecord::Base has_many :memberships has_many :cards, :through => :memberships validates_presence_of :cards end I also have

问题 Could Some one please explain to me what is going on here? This is an example that I put together to show y'all whats up: class Person include DataMapper::Resource property :id, Serial property :type, Discriminator property :name, String property :age, Integer end class Male < Person end class Father < Male property :job, String end class Son < Male end class Female < Person end class Mother < Female property :favorite_song, String end class Daughter < Female end DataMapper.auto_upgrade! If I

问题 Could Some one please explain to me what is going on here? This is an example that I put together to show y'all whats up: class Person include DataMapper::Resource property :id, Serial property :type, Discriminator property :name, String property :age, Integer end class Male < Person end class Father < Male property :job, String end class Son < Male end class Female < Person end class Mother < Female property :favorite_song, String end class Daughter < Female end DataMapper.auto_upgrade! If I

问题 I've read some of Bill Karwin's answers about single table inheritance and think this approach would be good for the setup I am considering: Playlist -------- id AUTO_INCREMENT title TeamPlaylist ------------ id REFERENCES Playlist.id teamId REFERENCES Team.id UserPlaylist ------------ id REFERENCES Playlist.id userId REFERENCES User.id PlaylistVideo ------------- id playlistId REFERENCES Playlist.id videoId REFERENCES Video.id All the CASCADE options are set to DELETE which will work

问题 Let's say I have two tables -- Products and Orders. For the sake of simplicity assume that only one product can be purchased at a time so there is no join table like order_items. So the relationship is that Product has many orders, and Order belongs to product. Therefore, product_id is a fk in the Order table. The product table is STI -- with the subclasses being A, B, C. When the user orders subclass Product C, two special validations must be checked on the Order model fields order_details