Relation is an API module and storage model for both simple and the most complex relations between entities. The module can handle both directional and symmetrical relations very well.

Relations are entities and can therefore have fields. This makes Relation the most flexible and powerful relation model out there. (Still, using Relation with anything but the default SQL storage will not work in most cases.)

Examples

John, Jen and Jack are siblings. This relation are symmetrical and points in all directions.

               |-- John
               |
Are siblings --|-- Jen
(relation)    |
               |-- Jack

CompanyA a made a donation to PartyB, with a transaction via BankC. Both relations (donation and transaction) are directional.

CompanyA   -->  DonationX   --> PartyB
(node)         (relation)      (node)
DonationX  --> TransactionY --> BankC
(relation)      (relation)      (node)

In the example above DonationX can have an integer field for the donation amount. This is something that no other relationship models in Drupal supports.

How to use

The Learn Relation module screencast series from NodeOne is a good start if you want to learn how to use this module:

  1. Introduction to Relation
  2. Creating a Simple Relation Type
  3. The Relation Widget
  4. Directional Fields and Fields on Relations
  5. Relation and Views - Part 1
  6. Details of Duplicate Rows
  7. More Relations and Views
  8. Using Relation with Rules
  9. Creating Relations with Rules, Part 2
  10. The Relation Add Block
  11. Relation Select

Configuring and creating relations

The Relation module itself provides a block that can be used to create relations. It's very simple and effective. It can also be done using Rules.

Listing relations

The Relation module has a very effective Views integration, both functionality wise and performance wise.

Related modules

Create relations

Display relations

  • Create graphs of all relations on your site with Graph API.

Projects using Relation

  • RedHen is a native drupal CRM. Relationships between CRM entities (e.g. contacts and organisations).
  • ERPAL is a full Drupal distribution aiming to manage almost any business related processes in service and project based companies, and includes a CRM, as well as management for projects, documents, employment, and invoices.
  • CRM Core provides a basic framework for managing contacts, activities and relationships within your Drupal website.

The future

Drupal (core and contrib) maintains too many different (inefficient) relation models (node authors, node comments, comment replies, entity references etc.). The goal is to replace them all with Relation module.

Credits

Credit goes to all the maintainers for building the module and to Itangalo for creating screencast documentation for this module. ITV started sponsoring chx's work on relation on December 6, 2011.

Rationale

While a similar module could be built based on Entityreference and Entity Construction Kit (ECK) by creating a custom entity and adding entity reference fields to it, this hypothetical module would not be able to

  1. refer different kinds of entities for one endpoint
  2. handle symmetrical relations in one API (for eg. a single rule can be fired for both ends of the relationship)
  3. list siblings with Views
  4. support revisions

Also, relation, while very capable, is a small module which works with many contrib modules but requires none. We keep the API module as small as possible, adding new features into submodules as much as possible.

Project Information

Downloads