entity-relationship

I am looking for a way to have a @OneToMany relation between two tables and having extra attributes in the join table and I am not able to find much useful examples around. Sorry if this sounds lame but can any suggest me a good way for it. If you have additional columns in the join table, it's not a join table anymore, and you need a way to get and set values in these columns. So the answer is simple: the table needs to be mapped as an entity. For example, let's say you have a Person entity and an Address entity. And the person has several addresses. Now let's say each address must be

I wish to know how to correctly set up Primary Keys in a Relation . E.g. we have ER-diagram which contain elements: Key attributes Weak key attributes Identifying relationships Associative entities In order to translate it into Relational Model we should do some tricks. All elements above deal with Primary Keys of relations but they all are Natural Keys - so we can leave them as is or replace with Surrogate Keys . Consider some cases. Case 1 Key Attribute is a name - so it must be of type CHAR or VARCHAR . Generally names become Key Attributes . Case 2 Two (or more) Identifying Relationships

I have created a cable database in Access, and I generate a report that has lists the connectors on each end of a cable. Each cable has its own ID, and 2 connector IDs, associated with it. All the connectors are from the same table and is linked to many other tables. I need 2 fields in one table (cable) associated with 2 records in the second table. My solution was to create 2 more tables: A primary connector table and secondary connector table, each of which has all entries from the first connector table. Then I could create columns in the cable ID Table for the primary and secondary IDs. The

I have a JPA (Hibernate) entity: @Entity class Transaction { @ManyToOne private Room room; } When I create a new Transaction , I know the ID of the Room that it should refer to (but don't have a Room object). Can I somehow create and persist a Transaction with just this info, or do I really need to: Room room = em.find(roomId, Room.class); em.persist(new Transaction(room, ...)); You can use EntityManager.getReference() to get a proxy of the related entity without accessing the database. This proxy is lazy-initialized and will be initialized only when you query anything other than the ID if the

I have the following class: public class User { public Guid Id { get; set; } public string Name { get; set; } public Couple Couple { get; set; } } public class Couple { public Guid Id { get; set; } public User Groom { get; set; } public User Bride { get; set; } } Important points: Bride and Groom properties are required One-to-one relationship In the User class, it is Couple required DbContext in OnModelCreating modelBuilder.Entity<User>().HasRequired(u => u.Couple).WithRequiredPrincipal(); modelBuilder.Entity<Couple>().HasRequired(u => u.Bride).WithRequiredDependent(); modelBuilder.Entity