model-associations | 易学教程

Validation failed Class must exist

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问题 I have been (hours) trouble with associations in Rails. I found a lot of similar problems, but I couldn't apply for my case: City's class: class City < ApplicationRecord has_many :users end User's class: class User < ApplicationRecord belongs_to :city validates :name, presence: true, length: { maximum: 80 } validates :city_id, presence: true end Users Controller: def create Rails.logger.debug user_params.inspect @user = User.new(user_params) if @user.save! flash[:success] = "Works!" redirect

Aggregation vs Composition vs Association vs Direct Association

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问题 I am reviewing my knowledge in object-oriented programming. Under the relationship between classes topic, I have encountered some relationships which are a bit ambiguous to me. I know dependency "uses-a" and inheritance "is-a" but I'm a bit unfamiliar with Aggregation, Composition, Association and Direct Association; also, which of them is "has-a" relationship. Some use Aggregation interchangeably with Association. What is Direct Association? Also, what is Composition? In UML diagrams, the

ExtJS 4: Models with Associations and Stores

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问题 Introduction I'm facing an application design problem with the Ext.data.Model class in ExtJS. I will try to develop my ideas to a very common online store scenario here, so you can follow me. I would really appreciate any comments on my thoughts and conclusions! Models Let's suppose you want to map the fact that " Every customer can order multiple products " to ExtJS. From the bare words one can identify these three models involved: Customer , Order , and Product . The Order in this case is

Rails association with multiple foreign keys

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I want to be able to use two columns on one table to define a relationship. So using a task app as an example. Attempt 1: class User < ActiveRecord::Base has_many :tasks end class Task < ActiveRecord::Base belongs_to :owner, class_name: "User", foreign_key: "owner_id" belongs_to :assignee, class_name: "User", foreign_key: "assignee_id" end So then Task.create(owner_id:1, assignee_id: 2) This allows me to perform Task.first.owner which returns user one and Task.first.assignee which returns user two but User.first.task returns nothing. Which is because task doesn't belong to a user, they belong

How do rails association methods work?

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How do rails association methods work? Lets consider this example class User < ActiveRecord::Base has_many :articles end class Article < ActiveRecord::Base belongs_to :user end Now I can do something like @user = User.find(:first) @user.articles This fetches me articles belonging to that user. So far so good. Now further I can go ahead and do a find on these articles with some conditions. @user.articles.find(:all, :conditions => {:sector_id => 3}) Or simply declare and associations method like class User < ActiveRecord::Base has_many :articles do def of_sector(sector_id) find(:all, :conditions

Same Model for Two belongs_to Associations

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问题 I have an model PointOfContact which has_many Systems . From the Systems side I want to identify the PointOfContact as either the technical_manager or project_manager (or both). While still only keeping the PointOfContact 1 time in the DB. My attempt follows: class System < ActiveRecord::Base belongs_to :project_manager, :class_name => 'PointOfContact' belongs_to :technical_manager, :class_name => 'PointOfContact' end class PointOfContact < ActiveRecord::Base has_many :systems end When I run

How do rails association methods work?

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问题 How do rails association methods work? Lets consider this example class User < ActiveRecord::Base has_many :articles end class Article < ActiveRecord::Base belongs_to :user end Now I can do something like @user = User.find(:first) @user.articles This fetches me articles belonging to that user. So far so good. Now further I can go ahead and do a find on these articles with some conditions. @user.articles.find(:all, :conditions => {:sector_id => 3}) Or simply declare and associations method

Rails association with multiple foreign keys

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问题 I want to be able to use two columns on one table to define a relationship. So using a task app as an example. Attempt 1: class User < ActiveRecord::Base has_many :tasks end class Task < ActiveRecord::Base belongs_to :owner, class_name: \"User\", foreign_key: \"owner_id\" belongs_to :assignee, class_name: \"User\", foreign_key: \"assignee_id\" end So then Task.create(owner_id:1, assignee_id: 2) This allows me to perform Task.first.owner which returns user one and Task.first.assignee which