nHibernate mapping for entity to multiple different parent entities (eg Addres -> Firm, Addres -> Client)

Question

Can someone help me with the best way to map the following situation in fluent nHibernate? The Address class is used in both Client and Company. How can I store it most efficient in SQL? And what should the mapping look like? I've thought about multiple options, but I'm not experienced enough with nHibernate for these situations:

1. use 1 address entity and 1 table and use a denominator column to distinguish between address for client and address for company -> how to implement this in nHibernate?

2. use 1 address entity and 2 tables (ClientAddresses and CompanyAddresses) --> but I can only define 1 table in the mapping of the class Address

3. use 2 address entities and 2 tables --> not so elegant

I've just stumbled upon this problem when I started implementing the company class and realized it also needed multiple addresses. Up till now I had a Address and Client class and had a one-to-many mapping between them. In the database the Address had an extra column called ClientId. But with introducing the Company class I'm stuck...

Any help would greatly be appreciated.

I'm currently working in the sharparch 1.5 framework, which uses automapping and my mapping files are like this:

public class AddressMap : IAutoMappingOverride<Address>
{
    public void Override(AutoMapping<Address> mapping)
    {
        mapping.Table("addresses");
        mapping.Id(x => x.Id, "AddressGuid")
             .UnsavedValue(Guid.Empty)
             .GeneratedBy.GuidComb();

        mapping.References(x => x.Client, "ClientGuid");

    }
}

Below some more code the illustrate the problem:

Address

public class Address
{
   public virtual string StreetLine1 { get; set; }
   public virtual string StreetLine2 { get; set; }
   public virtual string PostalCode { get; set; }
   public virtual string City { get; set; }
   public virtual string Country { get; set; }
}

which has the following table:

tablename = addresses
fields= AddressGuid, StreetLine1, StreetLine2, PostalCode, City, Country

Client

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

Company

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

Answer 1

You could model the relationships as a many-to-many: many companies to many addresses, and many clients to many addresses.

In both your Company and Client mappings:

mapping.HasManyToMany(x => x.Addresses);

This will create two additional tables: one mapping between companies and addresses, another mapping between clients and addresses.

In theory this could allow sharing situations (some companies and clients all sharing have the same address row) which you probably don't want, but as long as your application logic doesn't allow that to happen, you'll be fine and you won't have to do anything tricky with nhibernate.

Answer 2

It looks like you can implement #1 with nHibernate's <any> mapping. Note that in this case you cannot specify foreign-key constraints.

an example of <any>

Fluent nHibernate syntax