How would nhibernate handle tables that aren't really entities per say?

Question

Hi,

I understand how nhibernate would map a table like Users, and Addresses.

But what if I have a table like:

Users_Addresses with columns UserID, AndressID.

Would I have to create a mapping for this and make it like a normal entity? It is really a table that I would reference in a inner join.

Answer 1

With NHibernate, you design your code independent of the database layout. You don't have to (and don't should to) create classes that are exactly the same as your database tables and columns. Example:

public class User
{
    public IList<Address> Addresses { get; private set; }

    public int Id { get; set; }
}

The mapping depends on what the relationship between address and user is:

• Can a user have multiple addresses?
• Can multiple users have the same address?
• What do you want to inner join on what? (I would expect a many to many relationship here with an outer join)

In a scenario when a user has multiple addresses and those addresses can be used by different users, you can use many to many mapping to map the address. The mapping also depends on how you want to create your user and address classes.

• Is it logical to have a list of addresses in a user?
• Is it logical to have a list of users in an address?
• Can a user have the same address twice?

The idea of NHibernate is: write code the way you like it, and add mapping to a database to it later.

Answer 2

Address is usually considered a value type in the scenario you are discussing - it has no intrinsic identity outside of the User.

Value types in nHibernate are mapped as components. Collections of value types are mapped as a set of composite elements.

See https://www.hibernate.org/hib_docs/nhibernate/1.2/reference/en/html/components.html for details on how to do this.