many-to-many

I got a problem with a many to many association in my persistence layer. My scenario is the following: A user can has several roles and a role can have several user attached to it. During the tests I encountered a strange behavior. I created role object and several user objects. The role was set to each of the users. After this the users were saved using a DAO. Then one of the user gets loaded to check whether he got the role that was passed to him before saving the user object. Calling getRoles() on the user shows that the role was set correctly. To check whether the inverse direction also

I have entity classes A and C. They are mapping the tables tblA and tblC and have a many-to-many relationship between them, with tblB to map between them. tblB contains A_ID, C_ID and SetDate, the last one being the date it was set, thus an attribute to the relationship. My question is, how do I best map in this attribute? At the moment they're unmapped, like this: A: @ManyToMany(targetEntity=C.class, cascade={ CascadeType.PERSIST, CascadeType.MERGE } ) @JoinTable(name="tblB", joinColumns=@JoinColumn(name="A_ID"), inverseJoinColumns=@JoinColumn(name="C_ID") ) private Collection<C> Cs; C:

I have an MSSQL database which I am considering porting to CouchDB or MongoDB. I have a many-to-many relationship within the SQL db which has hundreds of thousands rows in the xref table, corresponding to tens of thousands of rows in the tables on each side of the relationship. Will CouchDB and/or MongoDB be able to handle this data, and what would be the best way of formatting the relevant documents for performant querying? Thanks very much. For CouchDB, I would highly recommend reading this article about Entity Relationships. One thing I would note in CouchDB is to be careful of attempting

I have a many-to-many relationship between People and Departments since one person can be in many departments. People Departments ------ ----------- pID pName deptID deptName 1 James 1 Engineering 2 Mary 2 Research 3 Paul 3 Marketing 4 Communications People_Departments ------------------ pID deptID 1 1 1 2 2 2 2 4 3 1 3 2 3 3 What I want is this: pName deptName James Engineering, Research Mary Research, Communication Paul Engineering, Research, Marketing If I do plain LEFT JOINs on the tables using the SQL below, I will get several rows related to one person: SELECT people.pName, departments

Please help an EF n00b design his database. I have several companies that produce several products, so there's a many-to-many relationship between companies and products. I have an intermediate table, Company_Product, that relates them. Each company/product combination has a unique SKU. For example Acme widgets have SKU 123, but Omega widgets have SKU 456. I added the SKU as a field in the Company_Product intermediate table. EF generated a model with a 1:* relationship between the company and Company_Product tables, and a 1:* relationship between the product and Company_Product tables. I

I have a question for designing the ManyToMany in EJB, how can a jointable has a property? Here is an example, the students and courses are ManyToMany, every student have many courses, and many students choose one course. @Entity public class Student implements Serializable { @Id @GeneratedValue(strategy = GenerationType.AUTO) Long id; String name; private Collection<Course> courses; @ManyToMany(mappedBy = "students",cascade=CascadeType.ALL) public Collection<Course> getCourses() { return this.courses; } public void setCourses(Collection<Course> courses) { this.courses = courses; } } @Entity