Question

I have 3 tables

People
 - id -pk
 - name

Roles
 - id -pk
 - roleName

Events
 - id -pk
 - title

and a join table

event_performers
 - event_id -pk
 - role_id -pk
 - people_id -pk

An Event has many Roles.
A Role is performed by a Person.
A Role is associated with many Events.
A Person can perform many Roles.

So what I would like is that when I get an event I can access a collection of Roles related to that event, and from the Roles I can get the Person who performed the Role.

I’m not sure how I would go about mapping this in Doctrine 2 ?

Answer 1

I ran into this same issue about a week ago. I polled the Doctrine IRC channel users for the best solution (or at least the one that’s most commonly practiced). Here’s how it’s done:

Create a new entity named something like EventsPeopleRoles with three properties mapped using @ManyToOne, $event, $person, and $role.

Each association should be mapped similar to this:

/**
 * @ManyToOne(targetEntity="Events", inversedBy="eventsPeopleRoles")
 * @JoinColumn(name="event_id", referencedColumnName="id", nullable=false)
 */
private $event;

Then in each of the three related entities, code the inverse side of the association like this:

/**
 * @OneToMany(targetEntity="EventsPeopleRoles", mappedBy="event")
 */
private $eventsPeopleRoles;

You then have the choice of either adding an $id property to your “join entity” or using a composite primary key as described here and adding a unique constraint annotation in the entity class definition. Note that composite foreign keys are only supported beginning in Doctrine 2.1.

I was skeptical about this solution because I don’t like the idea of creating an entity only for the purposes of a join. It seems like cheating or at least in contrast to ORM design principles. But I am confident this is the accepted solution (for now at least) among Doctrine experts.