Enhancement Request: Support for Bi-Directional Relationships

[raccoon70]

Description:
Payload CMS currently supports one-way relationships (e.g., belongsTo, hasMany). However, bi-directional relationships are often needed to ensure that related data stays synchronized in both directions (e.g., a Post with an Author, where changes to either are reflected in both models).

Motivation:
Bi-directional relationships will:
• Ensure data integrity between related models.
• Simplify querying and reduce manual relationship syncing.
• Improve the user experience when managing related data.

Proposed Solution:
• Add a bidirectional flag to relationship fields, or
• Provide built-in relationship types like belongsToMany and manyToMany to handle bi-directional syncing automatically.

Example Use Case:
A Project has multiple Collaborators, and Collaborators belong to multiple Projects. Changes in one model should update the other automatically.

const Project = { fields: [{ name: 'collaborators', type: 'relationship', relationTo: 'Collaborators', bidirectional: true }] };
const Collaborator = { fields: [{ name: 'projects', type: 'relationship', relationTo: 'Projects', bidirectional: true }] };

[JeremieLeblanc]

It sounds like you're looking for the new Join field in V3.0

https://payloadcms.com/docs/beta/fields/join