----- Mensaje original -----
De: Christian Henning
Hi there, beware I'm a new to Multiindex and haven't digested the whole capabilities of the library, yet.
In my example I have two entities that are connected via a foreign key. In this case the key is type of an int. When retrieving the objects from a database I end up having two containers containing those objects. In the code below there are a customer_row and a order_row class. There is a one-to_many relationship between them. One customer can have several order but one order is can only one customer. So, my goal is to find an way to create order objects that are pointing to the correct row objects.
So far, I don't really see how the MultiIndex lib can be of help for me. I have looked at the example six which I think came pretty close to my goal. So, taken this example, is it possible to use an key type instead of the car_manufacturer pointer?
Your design looks basically correct, but you can have a tighter relationship between order_rows and their associated customer_rows as follows: struct order_row { int _id; customer_table::iterator _customer_it; string _article; int customer_id() const { return _customer_it->_id; } order_row( int id, customer_table::iterator customer_it, const string& article ) : _id( id ), _customer_it( customer_it ), _article( article ) {} friend ostream& operator<<( ostream& os, const order_row& o ) { os << o._id << " " << o.customer_id() << " " << o._article << endl; return os; } }; ... typedef multi_index_container< order_row, indexed_by< ordered_unique< tag< primary >, BOOST_MULTI_INDEX_MEMBER(order_row,int,_id) >, ordered_non_unique< tag< foreign >, BOOST_MULTI_INDEX_CONST_MEM_FUN(order_row,int,customer_id) > >
order_table;
... order_table ot; ot.insert( order_row( 0, ct.find(97), "Book" )); ot.insert( order_row( 1, ct.find(97), "Car" )); ot.insert( order_row( 2, ct.find(97), "Dish Washer" )); Having things arranged this way allows to go from a given order_row to the associated customer info faster (constant time) than in your original design (logarithmic lookup on _customer_id). Depending on your usage scenarios this can be worthwile. [...]
Is there a more advanced way using the MultiIndex lib of combining two related objects so I can created my orders array? Or in different words can I structure my code more efficiently?
With the design I propose, looks to me like there is no compelling need to define an order object and populate the orders vector: you can work directly with order_table just as easily, and as efficiently. Does this sound good to you, or is there some additional aspect I'm missing? Joaquín M López Muñoz Telefónica, Investigación y Desarrollo