one-to-many

问题 I have an object model like that: Folder - simple structure with name etc. File - complex object containing reference to Folder in which it is contained. Folder doesn't know its Files and I don't want it to know. The relation is many-to-one and should be known on File's side only. Anyway, I would like to rely on my database's ON DELETE CASCADE feature, so that when I remove Folder, I want all Files within that Folder to be deleted automatically. I can't use NHibernate's cascading as there is

问题 I use myBatis to map a simple database (as an example). It consists of 4 models: User , Car , Tariff , Insurance . User has private List carList and private Tariff tariff and some other fields with getters and setters. Car has private Insurance insurance and some other fields with getters and setters. So I can map only 1st nesting level. I mean i can map User and its fields - Tariff and a List of Cars . But I can't map Insurance field of Car . What should I do? Here is my mapper.xml: <?xml

问题 This is a brain teaser for me, but hoping it's clear to someone more experienced. Having trouble sorting out the correct associations. I have three models: User, Recipient, Discussion Right now the associations are set up this way: Discussion belongs_to :user has_many :recipients User has_many :discussions, dependent: :destroy has_many :discussions, :through => :recipients Recipient belongs_to :user, dependent: :destroy belongs_to :discussion, dependent: :destroy When I try to create a

问题 Good morning, I am having a little trouble with model relationships in Eloquent, I need to link articles and images for those articles with an intermediate table. In the intermediate table I'd like to add the id's of both article and image, and I would like to retrieve all the images belonging to an article, what would be the best way to manage the relationship? Thanks in advance 回答1: You can use morphMany() relationship (Polymorphic Relationship) to solve your problem like this: UPDATE : The

问题 I want a data-structure that supports these specific 1:N relations :- 1#. Human raise 0-N Human 2#. Human has 0-N Dog 3#. Human cultivate 0-N Tree 4#. Dog is a house of 0-N Parasites . Note: - State in these relations are all temporary e.g. Human1 may raise Human2 , but after a year, Human1 may abandon Human2 . - All objects are inherited from BaseObject and has unique int ID. In all of the above relation, I want to be able to support these features :- F1. add relation e.g. human_dog-

问题 I have a One-Many relation with two Entities : Order: int OrderId string OrderNumber ... OrderItem: int ItemId int sequence decimal Quantity ... One Order Has multiple OrderItems , I want to write a Linq that return all orders with their items and items be sorted by sequence field. How can i write a query such as following query? Order myOrder = db.Orders.Include("OrderItems").Include("sequence").FirstOrDefault(x => x.OrderId == 3); 回答1: You can't do that without projecting the results into a

问题 I would like to create a grails domain class that links to itself. This related post suggests a solution but I can't get it to work: Grails domain class relationship to itself For one thing I don’t understand what comparable does and would need to add a int compareTo(obj) method. Adding the following to my code without implementing Comparable compiles, but grails crashes at runtime: //NavMenu parent SortedSet subItems static hasMany = [subItems: NavMenu] static belongsTo = [parent: NavMenu]

问题 Suppose each user has some numbers(IDs of props in a web game, e.g.) to store in a DB. I saw some implementations storing the numbers as a JSON string (representing an Array structure) in one field of the user's info table. But my intution is creating another table like below CREATE TABLE user_numbers ( userid INT, user_number, FOREIGN KEY (userid) REFERENCES user_info(id) ON DELETE CASCADE ); as it's the formal way for a one-to-many relationship. So I'm wondering does the JSON methods has

问题 Hallo all. I'm trying to map an association one-to-many to an entity that is mappes with @Inheritance(strategy=InheritanceType.JOINED) .... @ManyToMany @JoinTable(name = "S_MC_CC_CONTRATTIRAPPORTI", joinColumns = @JoinColumn(name = "COD_MULTICHANNELID"), inverseJoinColumns = @JoinColumn(name = "COD_RAPPORTO") ) private Collection<Rapporto> rapporti; ... @Entity @Table(name = "S_MC_CC_RAPPORTI") @Inheritance(strategy=InheritanceType.JOINED) @DiscriminatorColumn(name="COD_TIPORAPPORTO") public

问题 I have a (Java) batch pipeline that has follow the following pattern: (FileIO) (ExtractText > input=1 file, output=millions of lines of text) (ProcessData) The ProcessData stage contains slow parts (matching data against big whitelists) and needs to be scaled on several workers, which should not be an issue since it only contains DoFns. However it would seem that my one-to-many stage forces all the outputs to be processed only by one worker (instantiating more workers makes them all idle