Developer Introduction

What is MODX?¶

MODX Revolution is a content application platform: a CMS whose parts you extend with your own Snippets, Plugins, TVs and Manager pages.

What is MVC?¶

MVC — Model-View-Controller — splits an application three ways: the Model holds the data, the Controller talks to the Model, the View shows the result. You can change the View without touching the Model.

What is MVC²?¶

MODX extends this to MVC²: Model-View-Controller/Connector. The extra way to reach the Model from the View is the Connector — an AJAX entry point that calls a Processor.

Connector/Processor Relationships¶

A Connector is a gateway to Processors. It exists so nothing can call a Processor directly: the Connector decides who is allowed to run which Processor.

What is xPDO?¶

xPDO — open eXtensions to PDO — is the database layer of MODX (PHP 8.1+ required, see MODX 3 composer.json). It implements the Active Record pattern on top of PDO and lets you keep domain logic separate from database logic, or mix the two, as the task requires.

What is an ORM?¶

An ORM maps tables to classes: a table becomes a class, a row becomes an object, and the schema states the mapping. You work with objects; the library writes the SQL. See the object-relational model article for the general idea.

A Brief Overview of Revolution¶

MODX Revolution is a content management framework: not a general PHP application framework, and more than a fixed CMS. You build content applications out of its elements and its API. Internally it follows the MVC² layout described above.

The Model¶

The M is the Model: the core classes, prefixed mod in Revolution, that manipulate data records and hold the domain logic. This layer also includes Processors — scripts for form processing, REST and AJAX requests, roughly one per CRUD operation. Processors are never called directly; they run through a Connector.

The View¶

The V is the View: what the user sees. On the frontend the View is Templates, Chunks and Resources.

Templates¶

A Template is the page skeleton a Resource is rendered through — usually the head, header and footer markup in one place.

Chunks¶

A Chunk is a reusable fragment of HTML you insert in any Template, Chunk or Resource.

Resources¶

A Resource is one item in the site tree — a page, a file, a weblink or a symlink. The client requests it, and MODX renders it through a Template.

In the Manager¶

Manager views live in manager/templates/ as Smarty files.

The Controller¶

The Controller (C) differs by side: in the Manager it is PHP classes (see Controllers and Menus); on the frontend, modRequest routes the request and Snippets and Plugins do the page-level work.

Snippets¶

A Snippet is PHP you write in a Template, Chunk or Resource; MODX runs it on every request and inserts its return value into the page.

Plugins¶

A Plugin is PHP bound to system events: before the page is parsed, after it is rendered, before the request is routed, and so on. Use one for logic that spans the whole request — word censoring, link creation, cache handling, context redirection.

The 2nd C: The Connectors¶

A Connector is an entry point to Processors. The Manager uses them for every AJAX call that reads or writes data. Since 2.3 there are no per-element connector files: one front controller routes the action string to a processor class.

A request to connectors/index.php with action=resource/get and an id returns that Resource as JSON — provided the client has access. Every Connector request is checked against the Access Policy of the request’s Context; without access, the Connector refuses to return data.

See Also¶

1. Getting Started Developing
2. xPDO, the database layer for Revolution
3. Explanation of Directory Structure
4. Glossary of Revolution Terms