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From: JOAQUIN LOPEZ MU?Z (joaquin_at_[hidden])
Date: 2006-10-13 06:48:50

Hello Joe,

----- Mensaje original -----
De: Joe Gottman <jgottman_at_[hidden]>
Fecha: Jueves, Octubre 12, 2006 3:19 am
Asunto: [boost] [multi_index] Relationship Table
Para: boost_at_[hidden]

> 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<
> EmployeeExtractor;

typedef member<
> SkillExtractor;

> 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

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