Hello Joe, ----- Mensaje original ----- De: Joe Gottman <jgottman@carolina.rr.com> Fecha: Jueves, Octubre 12, 2006 3:19 am Asunto: [boost] [multi_index] Relationship Table Para: boost@lists.boost.org

One pattern that seems to come up pretty often is the relationship table. Suppose I have 2 classes, Employee and Skill. An Employee can have any number of Skills, and a Skill can be possessed by any number of Employees. But an Employee can have a given Skill only once. The user would need to be able to search for which Skills a given Employee has, and which Employees have a given Skill. What is the best way of using a multi_index_container to model this use case?

For instance, you can have the following (warning: uncompiled, beware typos): typedef std::pair< boost::reference_wrapper<const Employee>, boost::reference_wrapper<const Skill>

EmployeeSkillPair;

typedef member< EmployeeSkillPair, EmployeeSkillPair::first_type, &EmployeeSkillPair::first

EmployeeExtractor;

typedef member< EmployeeSkillPair, EmployeeSkillPair::second_type, &EmployeeSkillPair::second

SkillExtractor;

multi_index_container< EmployeeSkillPair, indexed_by< ordered_unique< composite_key< EmployeeSkillPair, EmployeeExtractor, SkillExtractor > >, ordered_non_unique< EmployeeExtractor >

EmployeeSkillRelations;

The first index enforces the uniqueness of a given Employee-Skill link and lets you obtain the Skills associated to an Employee (use equal_range passing the Employee of interest --inside a tuple due to the usage of composite keys, please consult the docs.) The second index lets you retrieve the Employees having a particular Skill.

Suppose, in addition, that every Employee who has a Skill has a numerical rating at that Skill. How would you do a multi_index_container in that case?

Augment EmployeeSkillPair to store this rating too.

Joe Gottman

Joaquín M López Muñoz Telefónica, Investigación y Desarrollo