# Code Overview

The bulk of pgAdmin is a Python web application written using the Flask framework on the backend, and HTML5 with CSS3,ReactJS on the front end. A desktop runtime is also included for users that prefer a desktop application to a web application, which is written using Electron.

## Runtime

The runtime is based on Electron which integrates a browser and the Python server creating a standalone application. The source code can be found in the /runtime directory in the source tree.

## Web Application

The web application forms the bulk of pgAdmin and can be found in the /web directory in the source tree. The main file is pgAdmin4.py which can be used to run the built-in standalone web server, or as a WSGI application for production use.

### Configuration

The core application configuration is found in config.py. This file includes all configurable settings for the application, along with descriptions of their use. It is essential that various settings are configured prior to deployment on a web server; these can be overridden in config_local.py or config_system.py (see the config.py documentation) to avoid modifying the main configuration file.

### User Settings

When running in desktop mode, pgAdmin has a single, default user account that is used for the desktop user. When running in server mode, there may be unlimited users who are required to login prior to using the application. pgAdmin utilised the Flask-Security module to manage application security and users, and provides options for self-service password reset and password changes etc.

Whether in desktop or server mode, each user’s settings are stored in a SQLite OR external database which is also used to store the user accounts. This is initially created using the setup.py script which will create the database file and schema within it, and add the first user account (with administrative privileges) and a default server group for them. A settings table is also used to store user configuration settings in a key-value fashion. Although not required, setting keys (or names) are typically formatted using forward slashes to artificially namespace values, much like the pgAdmin 3 settings files on Linux or Mac.

Note that the local configuration must be setup prior to setup.py being run. The local configuration will determine how the script sets up the database, particularly with regard to desktop vs. server mode.

## pgAdmin Core

The heart of pgAdmin is the pgadmin package. This contains the globally available HTML templates used by the Jinja engine, as well as any global static files such as images, Javascript and CSS files that are used in multiple modules.

The work of the package is handled in it’s constructor, __init__.py. This is responsible for setting up logging and authentication, dynamically loading other modules, and a few other tasks.

## Modules

Units of functionality are added to pgAdmin through the addition of modules. Theses are Python object instance of classes, inherits the PgAdminModule class (a Flask Blueprint implementation), found in web/pgadmin/utils.py. It provide various hook points for other modules to utilise (primarily the default module - the browser).

To be recognised as a module, a Python package must be created. This must:

1. Be placed within the web/pgadmin/ directory, and

2. Implements pgadmin.utils.PgAdminModule class

3. An instance variable (generally - named blueprint) representing that particular class in that package.

Each module may define a template and static directory for the Blueprint that it implements. To avoid name collisions, templates should be stored under a directory within the specified template directory, named after the module itself. For example, the browser module stores it’s templates in web/pgadmin/browser/templates/browser/. This does not apply to static files which may omit the second module name.

In addition to defining the Blueprint, the views module is typically responsible for defining all the views that will be rendered in response to client requests, we must provide a REST API url(s) for these views. These must include appropriate route and security decorators. Take a look at the NodeView class, which uses the same approach as Flask’s MethodView, it can be found in web/pgadmin/browser/utils.py. This specific class is used by browser nodes for creating REST API url(s) for different operation on them. i.e. list, create, update, delete, fetch children, get statistics/reversed SQL/dependencies/dependents list for that node, etc. We can use the same class for other purpose too. You just need to inherit that class, and overload the member variables operations, parent_ids, ids, node_type, and then register it as node view with PgAdminModule instance.

Most pgAdmin modules will also implement the hooks provided by the PgAdminModule class. This is responsible for providing hook points to integrate the module into the rest of the application - for example, a hook might tell the caller what CSS files need to be included on the rendered page, or what menu options to include and what they should do. Hook points need not exist if they are not required. It is the responsibility of the caller to ensure they are present before attempting to utilise them.

Hooks currently implemented are:

    class MyModule(PgAdminModule):
        """
        This is class implements the pgadmin.utils.PgAdminModule, and
        implements the hooks
        """

        ...

        def get_own_stylesheets(self):
            """
            Returns:
                list: the stylesheets used by this module, not including any
                      stylesheet needed by the submodules.
            """
            return [url_for('static', 'css/mymodule.css')]

        def get_own_javascripts(self):
            """
            Returns:
                list of dict:
                - contains the name (representation for this javascript
                  module), path (url for it without .js suffix), deps (array of
                  dependents), exports window object by the javascript module,
                  and when (would you like to load this javascript), etc
                  information for this module, not including any script needed
                  by submodules.
            """
            return [
                {
                    'name': 'pgadmin.extension.mymodule',
                    'path': url_for('static', filename='js/mymodule'),
                    'exports': None,
                    'when': 'server'
                    }
                ]

        def get_own_menuitems(self):
            """
            Returns:
                dict: the menuitems for this module, not including
                      any needed from the submodules.
            """
            return {
                'help_items': [
                    MenuItem(
                        name='mnu_mymodule_help',
                        priority=999,
                        # We need to create javascript, which registers itself
                        # as module
                        module="pgAdmin.MyModule",
                        callback='about_show',
                        icon='fa fa-info-circle',
                        label=gettext('About MyModule'
                        )
                    ]
                }
        def get_panels(self):
            """
            Returns:
                list: a list of panel objects to add implemented in javascript
                      module
            """
            return []
        ...

    blueprint = MyModule('mymodule', __name__, static_url_path='/static')

pgAdmin Modules may include any additional Python modules that are required to fulfill their purpose, as required. They may also reference other dynamically loaded modules, but must use the defined hook points and fail gracefully in the event that a particular module is not present.

## Nodes

Nodes are very similar to modules, it represents an individual node or, collection object on the object explorer treeview. To recognised as a node module, a Python package (along with javascript modules) must be created. This must:

1. Be placed within the web/pgadmin/browser/ directory, and

2. Implements the BrowserPluginModule, and registers the node view, which exposes required the REST APIs

3. An instance of the class object

## Front End

pgAdmin uses javascript extensively for the front-end implementation. It uses require.js to allow the lazy loading (or, say load only when required), ReactJS with CSS and MaterialUI for UI look and feel. We have divided each module in small chunks as much as possible. Not all javascript modules are required to be loaded (i.e. loading a javascript module for database will make sense only when a server node is loaded completely.) Please look at the javascript files node.js, browser.js, menu.js, panel.js, etc for better understanding of the code.