[odb-users] one-to-one relationship with shared primary keys

[Paul Harrison]

On 2015-01 -21, at 09:44, Boris Kolpackov <boris at codesynthesis.com> wrote:

> Hi Paul,
> 
> Paul Harrison <paul.harrison at manchester.ac.uk> writes:
> 
>> I have several tables with the same primary key, and a one-to-one
>> relationship between instances in the tables. I have been trying
>> to find a way to be able to have the object for one the tables
>> include shared pointers to the corresponding objects in the other
>> tables without any extra columns being used as foreign keys, but
>> have not been able to find a method of doing this with ODB - is
>> there a trick that I am missing?
> 
> You can use a database operation callback to implement this quite
> easily. Here the outline:
> 
> #pragma db object
> struct object1
> {
>  #pragma db id
>  int id;
> 
>  ...
> };
> 
> #include <odb/callback.hxx>
> 
> #pragma db object callback(init)
> struct object2
> {
>  #pragma db id
>  int id; // Also, implicitly, a foreign key to object1.
> 
>  ...
> 
>  #pragma db transient
>  std::shared_ptr<object1> obj1;
> 
>  void init (odb::callback_event e, odb::database& db)
>  {
>    if (e == odb::callback_event::post_load) 
>      obj1 = db.load<object1> (id);
>  }
> };
> 
> See Section 14.1.7, "callback" for more details on database operation
> callbacks.

Great - this does exactly what I want and prevents the need for db access code having to leak into parts of my code that should not have to know about the database.

thanks,
	Paul.