associations

问题 In this example, I create a user with no profile , then later on create a profile for that user. I tried using build with a has_one association but that blew up. The only way I see this working is using has_many . The user is supposed to only have at most one profile . I have been trying this. I have: class User < ActiveRecord::Base has_one :profile end class Profile < ActiveRecord::Base belongs_to :user end But when I do: user.build_profile I get the error: ActiveRecord::StatementInvalid:

问题 How would you do a many-to-many association with MongoDB? For example; let's say you have a Users table and a Roles table. Users have many roles, and roles have many users. In SQL land you would create a UserRoles table. Users: Id Name Roles: Id Name UserRoles: UserId RoleId How is same sort of relationship handled in MongoDB? 回答1: Depending on your query needs you can put everything in the user document: {name:"Joe" ,roles:["Admin","User","Engineer"] } To get all the Engineers, use: db

问题 What is the difference between Unidirectional and Bidirectional associations? Since the table generated in the db are all the same,so the only difference I found is that each side of the bidiretional assocations will have a refer to the other,and the unidirectional not. This is a Unidirectional association public class User { private int id; private String name; @ManyToOne @JoinColumn( name = "groupId") private Group group; } public class Group { private int id; private String name; } The

问题 In the Rails 3 docs, the build method for associations is described as being the same as the new method, but with the automatic assignment of the foreign key. Straight from the docs: Firm#clients.build (similar to Client.new("firm_id" => id)) I've read similar elsewhere. However, when I use new (e.g. some_firm.clients.new without any parameters), the new client's firm_id association is automatically created. I'm staring at the results right now in the console! Am I missing something? Are the

问题 In the Rails 3 docs, the build method for associations is described as being the same as the new method, but with the automatic assignment of the foreign key. Straight from the docs: Firm#clients.build (similar to Client.new("firm_id" => id)) I've read similar elsewhere. However, when I use new (e.g. some_firm.clients.new without any parameters), the new client's firm_id association is automatically created. I'm staring at the results right now in the console! Am I missing something? Are the

问题 I am using Ruby on Rails 3.2.13 and I would like to properly use the alias_method_chain :build, :option_name statement since I am getting a strange error. That is, ... ... in my controller file I have: class Articles::CommentsController < ApplicationController def create @articles_comment = @article.comments.build(params[:comment]) ... end end ... in my model file I have: class Articles::Comment < ActiveRecord::Base def self.build_with_option_name ... end alias_method_chain :build, :option

问题 I am using the validates_associated in a model to use the other model's validation code. The problem with this is the message for a failed validation is "..is invalid". I want to bubble the actual descriptive error form the model validation's failure to the top! I found this question: validates associated with model's error message Which had what looks like a very close solution: module ActiveRecord module Validations class AssociatedBubblingValidator < ActiveModel::EachValidator def validate

问题 I have a generic repository using EF6. The issue has to do with association properties requiring an "Include" even though it shouldn't. The following works: IQueryable<User> dbQuery = _db.Set<User>(); return dbQuery.Where(x => x.Child.Name == "Foo").ToList(); However, the following does not work: Func<User, bool> filter = x => x.Child.Name == "Foo"; IQueryable<User> dbQuery = _db.Set<User>(); return dbQuery.Where(filter).ToList(); It throws an "Object Reference not set..." exception on Child.

问题 Context: I have a Company model that has many projects . Each project has many tasks . The company has many employees . Employee belongs to Company and has many tasks . It is one employee per task and an employee will have only one task per project . Schema: Problem: I'm building a form to create a project where the user can add multiple tasks . Each task has an amount of hours specified and the employee performing the task . Upon submission the form should create a single project record, one

问题 As it currently stands, this question is not a good fit for our Q&A format. We expect answers to be supported by facts, references, or expertise, but this question will likely solicit debate, arguments, polling, or extended discussion. If you feel that this question can be improved and possibly reopened, visit the help center for guidance. Closed 7 years ago . supportData = {('ELF'): 0.75, ('CAT'): 0.75, ('BAT', 'CAT', 'ELF'): 0.5, ('ARK', 'BAT'): 0.25, ('ARK', 'ELF'): 0.25, ('CAT', 'ELF'): 0