one-to-many | 易学教程

Selecting primary keys that do not have foreign keys in another table

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问题 For simplification, I have two tables related with one to many using a foreign key, for example: Users table: id name Actions table: id user_id one user may have many actions or not. I need an sql select that returns users ids that don't have a user_id value in the actions table. Users Table: id name 1 John 2 Smith 3 Alice Actions Table: id user_id 1 3 2 1 So I need an sql query that returns the user id 2 (Smith) because the foreign key values don't include the id 2 I tried the following SQL,

hibernate one to many using a join table, and hibernate annotations

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问题 I want do a one-to-many relationship between two tables using a join table. This is why I want to use a join table: Hibernate unidirectional one to many association - why is a join table better? Why is it recommended to avoid unidirectional one-to-many association on a foreign key? Finally, I want to use Hibernate annotations to perform this. I found some examples to do this using xml mapping but nothing with annotations. I believe this would be how the tables need to be created CREATE TABLE

How to deal with Form Collection on Symfony2 Beta?

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问题 I have an entity User and an entity Address. There is a relation One-to-Many between User and Address : class User { /** * @orm:OneToMany(targetEntity="Address") */ protected $adresses; [...] } I have a class AddressType, and class UserType : class UserType extends AbstractType { public function buildForm(FormBuilder $builder, array $options) { $builder->add('addresses', 'collection', array('type' => new AddressType())); } [...] } In my controller, I build form with : $form = $this->get('form

How to implement a Counter Cache in Rails?

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I have a posts controller and a comments controller. Post has many comments, and comments belong to Post. The associate is set up with the counter_cache option turned on as such: #Inside post.rb has_many :comments #Inside comment.rb belongs_to :post, :counter_cache => true I have a comments_count column in my posts table that is defaulted to zero, as such: add_column :posts, :comments_count, :integer, :default => 0 In the create action of my comments controller, I have the following code: def create @posts = Post.find(params[:post_id]) @comment = @post.comments.build(params[:comment]) if

Creating PostgreSQL tables + relationships - PROBLEMS with relationships - ONE TO ONE

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问题 So I am supposed to create this schema + relationships exactly the way this ERD depicts it. Here I only show the tables that I am having problems with: So I am trying to make it one to one but for some reason, no matter what I change, I get one to many on whatever table has the foreign key. This is my sql for these two tables. CREATE TABLE lab4.factory( factory_id INTEGER UNIQUE, address VARCHAR(100) NOT NULL, PRIMARY KEY ( factory_id ) ); CREATE TABLE lab4.employee( employee_id INTEGER

Laravel - Form Input - Multiple select for a one to many relationship

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问题 One of the requirements in an application that I am building is for a form input which takes in a varying number of items for a single field. For instance, sports that I play are ('Soccer','Tennis','Croquet'). There are a finite number of sports one can play (arguably), so these items should be selected from a "drop down" type list in the form input. Downstream of this form will be two tables which have a one-to-many relationship. So from the above, the "user" table would have a single row,

Deriving UITableView sections from NSFetchedResultsController using “to many” relationship

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My Core Data model looks like this: article <--->> category Is it even remotely possible to use NSFetchedResultsController to produce a UITableView that looks something like this? Category 1 - Article A - Article B - Article C Category 2 - Article A - Article D - Article E - Article F Category 3 - Article B - Article C Specifically, I'm interested in the (edge?) case where each UITableView section has a unique title (eg, "Category 1", "Category 2"), but the same object can exist in multiple sections (eg, Article A exists in both Category 1 and Category 2). I have scoured Apple's Core Data docs

cleaning nullptr in one-to-many relation that use custom weak pointer

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I have a one-to-many map class - MyMap1N<WeakPtr_Parent,WeakPtr_Children> . By design, it is supposed to store weak pointers of game-related instance. Roughly speaking, it is called like :- MyMap1N<WeakPtr<Room>,WeakPtr<RigidBody>> map; WeakPtr<Room> room=create<Room>(); WeakPtr<RigidBody> body=create<RigidBody>(); map.add(room,body); MyArray<WeakPtr<RigidBody>> bodys=map.getAllChildren(room); By profiling, I found that std::unordered_map is too slow. Thus, I had to find another way to implement it. I decided to create an array (instead of unordered_map ) in Room . To increase speed of query,

envers multi level entity revision howto

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User have n Contacts. A Contact can have a localized Comment (Comments are shared between Contacts). Java Beans: @Audited @Entity public class User { @OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL, orphanRemoval = true) Set<Context> contacts; } @Audited @Entity public class Contact { @ManyToOne(fetch = FetchType.EAGER, cascade = { CascadeType.MERGE, CascadeType.PERSIST, CascadeType.REFRESH}) Comment comment; } @Audited @Entity public class Comment { String de; String en; String fr; } If I change the german localization (Comment.de) of a contact (Contact.comment) then this will

one to many with mongoose

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问题 I want to define a one-to-many relationship between my Student model and my Formation model: 1 student belongs to 1 formation and a formation can be composed of N students. My needs are: be able to populate a Formation document with its students easily retrieve the Formation of a Student So I wrote: let student = new Schema({ firstName: { type: String }, lastName: { type: String }, formation : { type: Schema.Types.ObjectId, ref: 'Formation' } }); let formation = new Schema({ title: { type: