one-to-many | 易学教程

SQLAlchemy one to many relationship, how to filter the collection

阅读更多关于 SQLAlchemy one to many relationship, how to filter the collection

问题 Bacially Product has a one to many relationship to ProductPicture . My product picture model looks like this: picture_type_enums = ('main', 'related', 'option') class ProductPicture(Base): __tablename__ = 'product_pictures' picture_id = Column(Integer, primary_key = True) product_id = Column(Integer, ForeignKey('products.product_id')) picture_type = Column(Enum(*picture_type_enums)) url = Column(String(120)) and my product model looks like this: class Product(Base): __tablename__ = 'products'

one-to-many IPC

阅读更多关于 one-to-many IPC

问题 I'm looking for an ipc mechanism which would allow high throughput of data updates from one process to many (thousands). The 'server' process would be responsible for updating a data structure at a high frequency. Upon update, I'd like to notify the 'client' processes of the update, and allow those processes to read the new data. Under a Linux or FreeBSD environment, what would be a good way to go about this? 回答1: I would recommend using ZeroMQ. It's a fast, lightweight, cross-platform, cross

One-to-many relationship: Update removed children with JPA 2.0

阅读更多关于 One-to-many relationship: Update removed children with JPA 2.0

问题 I have a bidirectional one-to-many relationship. 0 or 1 client <-> List of 0 or more product orders . That relationship should be set or unset on both entities: On the client side, I want to set the List of product orders assigned to the client; the client should then be set / unset to the orders chosen automatically. On the product order side, I want to set the client to which the oder is assigned; that product order should then be removed from its previously assiged client's list and added

JPA reference table mapping

阅读更多关于 JPA reference table mapping

There are two main @Entity classes reflecting these tables: TableA {id,name} TableB {id,name} And one reference table TableC {tableA.id,tableB.id} Question is: how to map a TableA 's entity's field with @OneToMany realation to TableB objects list: @OneToMany ?????????? private List<TableBEntity> tableBItems; If what you really have is a OneToMany (which means that a give tableB.id appears at most once in TableC ), then the mapping is the following: @OneToMany @JoinTable(name = "TableC", joinColumns = @JoinColumn(name = "TABLE_A_ID"), inverseJoinColumns = @JoinColumn(name = "TABLE_B_ID"))

Terminal mongo to one-to-many basic examples

阅读更多关于 Terminal mongo to one-to-many basic examples

There are a lot of " why not JOIN? " questions here, to understand who to use mongodb... But even the guide at model-embedded-one-to-many-relationships-between-documents not show the basic clues... There are to approaches: generate an array that contains the "embedded data" of the join, to produce "on fly" data. (using find() and what more simple algoritm?) use the db.collection.insert to produce "persistent data". So, if I am at mongo terminal, what the simplest way to do that? real-life dataset example At https://github.com/datasets/country-codes we have country-codes.csv : a table with ~250

Filter a one-to-many query by requiring all of many meet criteria

阅读更多关于 Filter a one-to-many query by requiring all of many meet criteria

How to implement a Counter Cache in Rails?

阅读更多关于 How to implement a Counter Cache in Rails?

问题 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

ViewModels and one-to-many relationships with Entity Framework in MVC?

阅读更多关于 ViewModels and one-to-many relationships with Entity Framework in MVC?

问题 I have an application for storing information about consultants in a database. The model is an Entity Framework model, and the database tables are Consultant with one-to-many relationships to a number of other tables (WorkExperiences, Programs, CompetenceAreas, etc). Now, when I want to create a new Consultant object in a View, I would really just want to pass a Consultant object as the model to the View. But for one, it has been suggested to me (Collection of complex child objects in Asp.Net

use the one-to-many or many-to-one

阅读更多关于 use the one-to-many or many-to-one

Two class: Department Task One department can have many tasks. One task can only belong to one department. So use one-to-many or many-to-one? one-to-many class Department{ private Set tasks; } class Task{ ...... } // Department.hbm.xml .... <set name="tasks"> <key column="departId" /> <one-to-many class="Task" /> </set> ..... many-to-one class Department{ } class Task{ Department depart; } // Task.hbm.xml .... <property name="depart"> <many-to-one class="Department" /> </property> ..... What's the difference? BTW,what is the difference between use the set and list? And example using list(xml

Ado.Net Entity : Object doesn't display linked members (foreign keys)

阅读更多关于 Ado.Net Entity : Object doesn't display linked members (foreign keys)

I have a simple databasescheme: User, Account. User has 1-to-many relationship with Account. I have generated a ado.net entity data model, and I can create users and accounts, and even link them together. In the database the account.user_id is correctly filled, so theoretically I should be able to acces User.Account.ToList() in C# through entity. However, When I try to acces User.Account.ToList() I get zero results. User user = db.User.First(U => U.id == 1); List<Account> accounts = user.Account.ToList(); ##count = 0... When I add the following code before the previous code it suddenly gives