associations

问题 I'm using Rails Admin on one of my sites. It's great so far, but I can't figure out how to remove a related object from an edit page. Example: I have two models Property and PropertyImage. class Property has_many :property_images, :dependent => :destroy end class PropertyImage belongs_to :property end I can go to the edit screen for an instance of either model, and I can delete PropertyImages from their list view. But when I edit a Property, I want to be able to delete a PropertyImage that's

问题 So i'm making a web app using ROR and I can't figure out what the right syntax for this form is. I'm currently making an association type of code for comments and posts. <%= form_for @comment do |f| %> <p> <%= f.hidden_field :user_id, :value => current_user.id %> <%= f.label :comment %><br /> <%= f.text_area :comment %> </p> <p> <%= f.submit "Add Comment" %> </p> <% end %> 回答1: Your form is fine, except the first line (and you don't need a hidden field for the user_id, thats done through your

问题 If I have two models: class Post < ActiveRecord::Base belongs_to :user end and class User < ActiveRecord::Base has_many :posts end If I do: post = Post.new user = User.new post.user = user post.save Does the user get saved as well and the primary key properly assigned in post 's user_id field? 回答1: ActiveRecord belongs_to associations have the ability to be autosaved along with the parent model, but the functionality is off by default. To enable it: class Post < ActiveRecord::Base belongs_to

问题 I have a database with 6500 players and each player has an average of 15 game results . Use case I want to generate a list of players, ordered by the sum of their prize money (a field in the results table). I prefer this to be in some sort of scope, so I can also filter the list on the player's country, etc. Performance I have seen posts that mention a cache_counter field for performance. In my case I have thousands of result records (75.000+) so I don't want the calculations being done every

问题 I'm currently having some trouble understanding ternary associations in UML. I get the binary ones, but I am unsure how multiplicity works on ternary. I'm doing exercises that I got from my university, the current one goes like this: One department may sell many products, but only to one market. On a market one product may only be sold by one department. I've read on different sources about how I'm supposed to think about a pair of the two classes I'm not trying to figure out the multiplicity

问题 I am curious as to why the record contained in the result set of a Model.save() response does not properly return updated associated data, despite the updated data being contained in the server response... Example Model & Store Definition: Ext.define("App.model.test.Parent",{ extend: 'Ext.data.Model', requires: ['App.model.test.Child'], fields: [ {name: 'id', type: 'int' }, {name: 'name', type: 'string'}, {name: 'kids', type: 'auto', defaultValue: []} ], idProperty: 'id', hasMany: [{

问题 Hey we have three tables in our database which are connected through two relationships which are Account and Invoices. Accounts (id....) Invoices (id, sender_id, receiver_id) Relationships (id, sender_id, receiver_id) Sender and receiver are both foreign keys which reference the account table so in cakePHP an account_id. The relationship table specifies relationships where invoices can be sent or received and the invoice table displays the invoices that have been sent. How do we link both

问题 I have two entities: Employee and Team . What I want is an EmployeeForm that has the Name of the Team . How can I achieve this using AutoMapper ? My current "solution" is the following: Mapper.CreateMap<Employee, EmployeeForm>() .ForMember(dest => dest.TeamName, opt => opt.MapFrom(x => x.GetTeams().FirstOrDefault() != null ? string.Join(", ", x.GetTeams().Select(y=>y.Name)) : "n/a")); In my opinion this is bad readable. What I would like to have is a generic method where I can pass an entity,

问题 I have a question about association multiplicity. I understand it, but for example if I would have: --------- --------- | |1 * | | |CLASS |----------| STUDENT | | | | | --------- --------- does that mean that at ANY point during system existence there must be at least 1 student assigned to the class, or those multiplicities should be true, if the system is operating normally? I am asking this question, because I was wondering about the moment of creation for an object. First we create an

问题 I have an important model in my application, with many associations. If I want to check all the references in a before_destroy callback, i'd have to do something like: has_many :models_1 has_many :models_2 mas_many :models_3 .... .... has_many :models_n before_destroy :ensure_not_referenced def :ensure_not_referenced if models_1.empty? and models_2.empty? and models_3.empty? and ... and models_n.empty? return true else return false errors.add(:base,'Error message') end end The question is, is