associations

问题 I have two classes, Master and Slave . The Master class has_one slave , the Slave class belongs to master . Given two associated objects, master_a and slave_a (where slave_a belongs to master_a ), how can I unlink them without destroying slave_a from the database? I essentially need to "free-up" slave_a . I've tried master_a.slave.delete , which destroys slave_a from the database. I've also tried master_a.slave.update_attribute(:master_id, nil) , but next time master_a.save is called, it

问题 In my application, I have to models: Workflow and Step; steps belongs_to workflow and a workflow has_many steps. Steps have an index and a boolean status ('completed'). I want to retrieve workflows whose step 1 is completed and step 2 is not, i.e. something like this in SQL: SELECT * FROM workflows w INNER JOIN steps s1 ON s1.workflow_id = w.id INNER JOIN steps s2 ON s2.workflow_id = w.id WHERE s1.index = 1 AND s1.completed = 1 AND s2.index = 2 AND s2.completed = 0 I've tried to express this

问题 I have associated a file extension with my Delphi 2009 program. I have been using the command line call method to pass the filename to my Delphi program so it can be opened. However, I found that when selecting multiple files, and clicking on them all at once, it opens each file in a separate instance of my program. I asked about this, and apparently the solution is to use one of the other two Windows methods: DDE or IDropTarget. But DDE is being deprecated, and MSDN recommends the

问题 This question is about a WPF application. I would like to open some associated files with my custom application. I found the way to open associated files. but still, I don't know how to handle dupplicated application. For example, if I click 'a.txt2', my app opens it. And I click 'a2.txt2', it also opens another process of my app. I want to get second click info only in the first app, not the execution of my app when associated files are clicked many. It's similar to 'notepad ++' open file to

问题 I have two models, Video and Frame. Frame.belongsTo(models.Video); Video.hasMany(models.Frame, { as: "Frames" }); I now need a way to specify first and last frame for a video, but can't get it to work. I tried this: Video.hasOne(Frame, { as: "FirstFrame" }); Video.hasOne(Frame, { as: "LastFrame" }); but that creates FirstFrameId and LastFrameId in the Frames table instead of the Videos table. I need to have video.get/setFirstFrame() and video.get/setLastFrame() functions available. How can I

问题 Hi I am trying to associate my User model with login model and Question_details models.But if i am using the Question_details association then i am geeting eagerLodingError :user is not associated to login but if i am commenting it then it works fine so how can i associate it ? But if i am associating with User Model module.exports = (sequelize, DataTypes) => { var Users = sequelize.define('users', { name: { type: DataTypes.STRING(100) } phone: { type: DataTypes.BIGINT, unique: true } }, {

问题 The Problem: I have a cakephp 3.x query object with two nested associations, Organizations.Positions.Skills , that is being set to a view variable, $Organizations . I'm trying to sort the query's resulting top level array by a column in the first nested association. That is, I want to sort $Organizations by a column in Positions , specifically Positions.Ended ). public function index() { $this->loadModel('Organizations'); $this->set('Organizations', $this->Organizations->find('all') ->contain

问题 I am relatively new to Rails and am working on a project that involves multiple, "nested" levels of data. I am having issues making the proper associations so I can get all the child elements of a model 3 levels higher. Here is an example of the models: class Country < ActiveRecord::Base has_many :states end class State < ActiveRecord::Base belongs_to :country has_many :cities end class City < ActiveRecord::Base belongs_to :state has_many :people end class Person < ActiveRecord::Base belongs

问题 I drives me crazy how many books contradicts themselves. Class A {} class B {void UseA(A a)} //some say this is an association, no reference is held but communication is possible Class A {} class B {A a;} //some say this is aggregration, a reference is held But many say that holding a reference is still just an association and for aggregation they use a list - IMHO this is the same, it it still a reference. I am very confused, I would like to understand the problem. E.g. here: http:/

问题 I am studying Belongs_to association, I have used following models, in that every order belongs to the customer, so I have used belongs_to in order model it giving error while creating order undefined method `orders' for # when I use has_many :orders in customer model it works fine, why it does not work with only belongs_to Its work with has_many :orders in customer model but not with has_one : order in customer controller it giving same above error. thanks in advance. Model :- order.rb class