Chapter 1: Architecture Overview

Multitier application

Juniper follows a multitier architecture, meaning that the presentation, the business logic and the data storage are separated. More specifically, it uses a three-tier architecture (image from Wikipedia):

The presentation tier is a combination of HTML5, JavaScript and CSS. The logic tier is exclusively written in Python, while the data tier only supports PostgreSQL as an RDBMS.

Depending on the scope of your module, Juniper development can be done in any of these tiers. Therefore, before going any further, it may be a good idea to refresh your memory if you don’t have an intermediate level in these topics.

In order to go through this tutorial, you will need a very basic knowledge of HTML and an intermediate level of Python. Advanced topics will require more knowledge in the other subjects. There are plenty of tutorials freely accessible, so we cannot recommend one over another since it depends on your background.

For reference this is the official Python tutorial.

Note

Since version 15.0, Juniper is actively transitioning to using its own in-house developed OWL framework as part of its presentation tier. The legacy JavaScript framework is still supported but will be deprecated over time. This will be discussed further in advanced topics.

Juniper modules

Both server and client extensions are packaged as modules which are optionally loaded in a database. A module is a collection of functions and data that target a single purpose.

Juniper modules can either add brand new business logic to an Juniper system or alter and extend existing business logic. One module can be created to add your country’s accounting rules to Juniper’s generic accounting support, while a different module can add support for real-time visualisation of a bus fleet.

Everything in Juniper starts and ends with modules.

Terminology: developers group their business features in Juniper modules. The main user-facing modules are flagged and exposed as Apps, but a majority of the modules aren’t Apps. Modules may also be referred to as addons and the directories where the Juniper server finds them form the addons_path.

Composition of a module

An Juniper module can contain a number of elements:

Business objects

A business object (e.g. an invoice) is declared as a Python class. The fields defined in these classes are automatically mapped to database columns thanks to the ORM layer.

Object views

Define UI display

Data files

XML or CSV files declaring the model data:

• views or reports,

• configuration data (modules parametrization, security rules),

• demonstration data

• and more

Web controllers

Handle requests from web browsers

Static web data

Images, CSS or JavaScript files used by the web interface or website

None of these elements are mandatory. Some modules may only add data files (e.g. country-specific accounting configuration), while others may only add business objects. During this training, we will create business objects, object views and data files.

Module structure

Each module is a directory within a module directory. Module directories are specified by using the --addons-path option.

An Juniper module is declared by its manifest.

When an Juniper module includes business objects (i.e. Python files), they are organized as a Python package with a __init__.py file. This file contains import instructions for various Python files in the module.

Here is a simplified module directory:

module
├── models
│   ├── *.py
│   └── __init__.py
├── data
│   └── *.xml
├── __init__.py
└── __manifest__.py

Juniper Editions

Juniper is available in two versions: Juniper Enterprise (licensed & shared sources) and Juniper Community (open-source). In addition to services such as support or upgrades, the Enterprise version provides extra functionalities to Juniper. From a technical point-of-view, these functionalities are simply new modules installed on top of the modules provided by the Community version.

Ready to start? Before writing actual code, let’s go to the next chapter to review the Juniper installation process. Even if Juniper is already running on your system, we strongly suggest you go through this chapter to make sure we start on the same page during the development of our new application.