How create an extra field in an unidirectional many-to-many relation? - symfony

Question

I found this response: https://stackoverflow.com/a/9135093/620095, but I wouldn't like to use a new class. I'm looking for the best way (elegant and straightforward).
Here is the 'Tag' entity:
MyApp\CoreBundle\Entity\Tag:
type: entity
table: tag
id:
id:
type: integer
generator: { strategy: AUTO }
fields:
name:
type: string
length: 255
nullable: false
The 'Post' entity:
MyApp\PostBundle\Entity\Post:
type: entity
table: post
id:
id:
type: integer
generator: { strategy: AUTO }
fields:
title:
type: string
length: 255
nullable: false
content:
type: text
nullable: false
manyToMany:
Tags:
targetEntity: MyApp\CoreBundle\Entity\Tag
joinTable:
name: post_tag
joinColumns:
post_id:
referencedColumnName: id
inverseJoinColumns:
tag_id:
referencedColumnName: id
The 'Event' entity:
MyApp\EventBundle\Entity\Event:
type: entity
table: event
id:
id:
type: integer
generator: { strategy: AUTO }
fields:
title:
type: string
length: 255
nullable: false
content:
type: text
nullable: false
manyToMany:
Tags:
targetEntity: MyApp\CoreBundle\Entity\Tag
joinTable:
name: event_tag
joinColumns:
event_id:
referencedColumnName: id
inverseJoinColumns:
tag_id:
referencedColumnName: id
Suppose I want a 'description' field in the 'event_tag' table. What should I do?
UPDATE: If is impossible, how would stay my three yml to add the quoted field?

Answer 1

Sorry, you have to create a new entity.
You have to considere this entity as an individual symfony entity
For example:
Product >- Stock -< Store
Product >- Bill -< User
...
And not as a link between two others entities.

Answer 2

#cbacelar "I updated the question. Can you help me?" => Event-Tag relationship could be sth like:
In Event entity, change manyToMany by oneToMany:
oneToMany:
EventTags:
targetEntity: MyApp\EventBundle\Entity\EventTag
mappedBy: Events
In Tag entity, change manyToMany by oneToMany:
oneToMany:
EventTags:
targetEntity: MyApp\EventBundle\Entity\EventTag
mappedBy: Tags
Create MyApp\CoreBundle\Entity\EventTag entity:
type: entity
table: event_tag
id:
id:
type: integer
generator: { strategy: AUTO }
fields:
description:
type: text
nullable: false
manyToOne:
Events:
targetEntity: MyApp\EventBundle\Entity\Event
inversedBy: EventTags
joinColumn:
name: event_id
referencedColumnName: id
Tags:
targetEntity: MyApp\CoreBundle\Entity\Tag
inversedBy: EventTags
joinColumn:
name: tag_id
referencedColumnName: id
`