many-to-many

I am trying to create Groups, Users and Memberships (the many-to-many relationships) simultaneously. People can add users to the group as they create it and then I want it to route through to a view of the group with all the members. I can get the users to be created and the current user's membership to save to the database. However I'm struggling to get the id for the freshly created User objects in order to save the new memberships. Group.rb class Group < ActiveRecord::Base has_many :memberships has_many :users, :through => :memberships has_many :users accepts_nested_attributes_for :users,

I'm having trouble figuring out how to set up JPA persistence (using EclipseLink and transaction-type="RESOURCE_LOCAL") correctly for the following entities: @Entity public class User { // snip various members @ManyToMany private List<Company> companies; public void setCompanies(List<Company> companies) { this.companies = companies; } } @Entity public class Company { // snip various members } What I'm trying to do is set up a cascade for the companies list so that, if a new Company that hasn't been previously persisted is in the list, it would be automatically persisted together with the User:

So I asked this question yesterday, but the goal posts have changed and the question is different: Hibernate / JPA Collection of Elements with Many to Many relationship? I want to know if it's possible to create entities that will model my required relationship so that Hibernate will create my schema when I fire up my application. The relationship I want looks like this: 1 http://a8.sphotos.ak.fbcdn.net/hphotos-ak-ash4/417593_10150594114269218_505554217_8657377_1475865815_n.jpg The thing is that the Join table can actually contain rows that don't link to any Elements. The structure represents

I've the following entities mapping: @Entity @Table(name = "books") public class Book implements Serializable { @ManyToMany @JoinTable(name="books2categories", joinColumns=@JoinColumn(name="book_id"), inverseJoinColumns=@JoinColumn(name="category_id")) Collection<Category> categories; ... @Entity @Table(name = "categories") public class Category implements Serializable { @ManyToMany(mappedBy="categories") private Collection<Book> books; BookRepository interface is looked: public interface BookRepository extends JpaRepository<Book, Long> { @Query("SELECT b FROM Book b INNER JOIN b.categories c

What is the reason for setting MappedBy in bidirectional many-to-many relationships? When one table has significant amount of records, while other has a few, which side is better to put mappedBy? It's actually a good question, and it helps to understand the concept of an "owning" entity. If you want to prevent both sides (in a bidirectional relationship) from having join tables , a good idea, then you need to have a mappedBy= element on one side. Whether or not there is a join table is controlled by the mappedBy="name" element of the @ManyToMany annotation. The Javadoc for mappedBy for the

I've read through scores of questions on here that seem at first to have a similar problem but just don't seem quite the same. Massive apologies if this is answered somewhere but like I say I've read through loads and can't find an answer. I'm using Entity Framework and MVC 3. I'm trying to add tags to products in my entity framework, which have a many to many relationship and a table linking them with simply the two keys in the link table, so EF condenses the Tags into a property of Product. Tables are set up like so: Product: ProductID [int, primary key], Name, etc. Tags: TagName [string,