relationship

问题 In database design what do n:m and 1:n mean? Does it have anything to do with keys or relationships? 回答1: m:n is used to denote a many-to-many relationship ( m objects on the other side related to n on the other) while 1:n refers to a one-to-many relationship ( 1 object on the other side related to n on the other). 回答2: 1:n means 'one-to-many'; you have two tables, and each row of table A may be referenced by any number of rows in table B, but each row in table B can only reference one row in

问题 What is the difference between attach() and sync() in Laravel 4\'s Eloquent ORM? I\'ve tried to look around but couldn\'t find anything! 回答1: attach(): Insert related models when working with many-to-many relations No array parameter is expected Example: $user = User::find(1); $user->roles()->attach(1); sync() Similar to the attach() method. sync() also use to attach related models. However main difference is: Sync method accepts an array of IDs to place on the pivot table Secondly, most

问题 7.3.3 Association(from kernel) ,page 36,UML superstructure ,v2.4.1: an association either owned by classifier or by relationship. Is there a real-life example in UML about association owned by classifier and association owned by relationship? 回答1: Chriss I hope this simple example helps. Guess you have a Java class public class A { private B b; ... } In UML you would model this relationship as an association from A to B: A -> B with the following modeling elements: Class B Class A + Property

问题 I\'m aware of the conceptual differences between Aggregation and Composition. Can someone tell me the implementation difference in Java between them with examples? 回答1: Composition final class Car { private final Engine engine; Car(EngineSpecs specs) { engine = new Engine(specs); } void move() { engine.work(); } } Aggregation final class Car { private Engine engine; void setEngine(Engine engine) { this.engine = engine; } void move() { if (engine != null) engine.work(); } } In the case of

问题 I\'ve found the concept and meaning behind these methods to be a little confusing, is it possible for somebody to explain to me what the difference between has and with is, in the context of an example (if possible)? 回答1: With with() is for eager loading . That basically means, along the main model, Laravel will preload the relationship(s) you specify. This is especially helpful if you have a collection of models and you want to load a relation for all of them. Because with eager loading you