relationship | 易学教程

How does Parse.com create a bidirectional relationship in the iOS client?

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问题 I'm following this tutorial: https://parse.com/tutorials/one-to-many-relationships I see a Post is created and the current user attached. But I don't see the opposite, I don't see how the Post is attached to the user. And at the end it says: "The application should now be able to create Post objects, set a one-to-many relationship between Posts and PFUsers, as well as use a query to obtain all Posts associated with a given user." How is that possible? If I use that code, how can I retrieve

wrong user_id being stored when creating a new record

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问题 So just got some help on this, but now have a new issue...I'm trying to list all of the 'commits' (these are basically simple edits) for a certain project. This is currently working but when I try to list the user who created the commit it is showing the wrong user profile picture (or name, etc). What is happening is the person who created the project is currently also the user_id for all commits. i.e, User A creates the project...then User B comes and adds a commit. But its showing User A as

Laravel 4 Relationship: messaging system

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问题 I followed the suggestions from user ehp in order to build a lightweight messaging-system: https://stackoverflow.com/a/18717864/1084315 Users: id | username Messages: id | from | content user_messages: user_id | message_id class User extends Eloquent { public function messages() { return $this->belongsToMany('Message'); } public function sent_messages() { return $this->hasMany('Messages', 'from'); } } class Message extends Eloquent { public function from() { return $this->belongsTo('User',

neo4j中索引的使用

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neo4j可以对node和relationship中的属性建立索引，索引中的node（relationship）和属性对key-value为多对多的关系。一个node(relationship)可以在某索引中存储多个属性对，一个属性对也可以对应到多个node(relationship)。代码： Node node1 = graphDb.createNode(); node1.setProperty("name","easypoint"); Node node2 = graphDb.createNode(); node2.setProperty("name","csdn"); nodeIndex.add(node1,"name",node1.getProperty("name")); nodeIndex.add(node1,"name","haha"); nodeIndex.add(node2,"name",node2.getProperty("name")); nodeIndex.add(node2,"name","haha"); for(Node node :nodeIndex.get("name","haha")){ System.out.println(node.getProperty("name")); } 结果： easypoint csdn 在neo4j中

Rails 4 has_and_belongs_to_many

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问题 I have two models. Venues and Categories. They are related to each other as has_and_belongs_to_many Categories are pre populated and in the form i want to display a multi-select to allow choosing the categories for a venue while adding a venue. venue.rb class Venue < ActiveRecord::Base has_and_belongs_to_many :categories end category.rb class Category < ActiveRecord::Base has_and_belongs_to_many :venues end Join Table create_table "categories_venues", id: false, force: true do |t| t.integer

sugarCRM : creating relationship using module loader, package not installing

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问题 I am trying to create relationships through module loader in SugarCRM. But the problem is my package is stopped installing after 55%. When I am viewing display log the error is:- Failed to copy cache/upgrades/temp/SYWr9G/custom/metadata/accounts_contacts_1MetaData.php custom/metadata/accounts_contacts_1MetaData.php I tried to change permissions also but at some point they through internal server error 500. Following are the code which I am using. 1.In manifest.php file : $installdefs = array(

How to plot relationships in R?

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问题 The relationship is expressed as a matrix x like this: John Jack Mary Wendy John 0 2 1 1 Jack 2 0 1 0 Mary 1 1 0 1 Wendy 1 0 1 0 The entries refer to the number of connections they have. Could anyone show me how to plot it as a network in R? Thanks! 回答1: This is known as an adjacency matrix. There is some information in the R FAQ on plotting social networks expressed as matrices: Plotting social network data can be easily done with the igraph package in R. [...] In order for the igraph

How to I design a database constraint so two entities can only have a many to many relationship if two field values within them match?

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问题 I have a database with four tables as follows: Addressbook -------------------- id more fields Contact --------------------- id addressbook id more fields Group --------------------- id addressbook id more fields Group to Contact --------------------- Composite key Group id Contact id My relationships are one to many for addressbook > contact, one to many for addressbook > group and many to many between contact and groups. So in summary, I have an addressbook. Contacts and groups can be

Ember.js: How to represent a has-many model relationship?

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问题 I am trying to set up an ember app where I have many Items, all of which have many Options. I then need a 'dashboard' area where I can monitor information on all Items/Options. In a previous post I got a working example of a dashboard which monitors a single collection of Items. How do I update this to represent child Options for each Item? Javascript - from jsBin (updated) App = Ember.Application.create(); /* ROUTES */ App.Router.map(function() { this.resource('items'); this.resource(

JPA - Removing of elements of a bidirectional Relationship

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问题 Why can i remove elements of a bidirectional relation although only one side of the relation is managed in persistence context (Example I)? When i have an unidirectional Relationship that doesn't work (see Example II). Why? Entities: @Entity Class User { ... @OneToMany(mappedBy = "user") private List<Process> processes; @OneToOne // Unidirectional private C c; ... @PreRemove private void preRemove() { for (Process p : processes) { p.internalSetUser(null); } } ... } @Entity Class Process { ...