Chapter 11. Flask and GeoAlchemy2

Python has always had strong internet capabilities. The standard library includes models for HTTP processing, STMP messages, and URL requests. Thousands of third-party modules have been written to extend or improve the built-in web functionality. Over time, a few modules coalesced into Python web frameworks—code libraries written to manage the creation and maintenance of complex and dynamic websites.

To better understand how to use a Python web framework and how to add geospatial capabilities, we'll implement the Flask Model View Controller (MVC) framework. A pure Python web framework, Flask can be combined with SQLAlchemy, GeoAlchemy2, and the Jinja2 HTML template system to create geospatially-enabled web pages.

In this chapter, you will learn about:

• The Flask web framework
• SQLAlchemy database management
• GeoAlchemy2
• Connecting to PostGIS using object-relational mapping (ORM)
• The Jinja2 web page template system

Flask and its component modules

Flask, as opposed to Django and GeoDjango (covered in Chapter 12, GeoDjango), does not include batteries. Instead, it allows a number of supporting modules to be installed as needed. This gives more freedom to you as the programmer, but it also makes it necessary to install the required components separately.

I've chosen some modules for this chapter that will allow us to create a Flask application with a geospatial component. The following sections will detail how to set up, install, and utilize these modules to generate a website, using a demonstration site with a PostGIS database backend (as covered in Chapter 7, Geoprocessing with Geodatabases) and the ability to perform spatial queries through a web-based interface.

Setup

A number of important Python modules must be in place to ensure that the Flask application and its connection to the PostgreSQL and PostGIS database components, will run as required. These modules will be downloaded and installed using...

Summary

In this chapter, we learned how to use the Flask MVC web framework and some of the available component modules that add extra functionality. These modules include the SQLAlchemy ORM, the GeoAlchemy2 ORM for geospatial queries, WTForms for processing of web data, and the Jinja2 templating system for creating web page templates. We created database tables, added data tables and tables relationships, and created a web application that utilized geospatial and relationship queries to generate dynamic web pages.

A fun challenge, building on the code reviewed here, would be to explore adding editing capabilities to the Arena application, allowing the user to move the arenas into their correct location if the data is out of date. Explore the GeoAlchemy2 ORM documentation for more advanced capabilities.

In the next chapter, we will review a similar MVC web framework, Django, and its GeoDjango spatial component. With more batteries included philosophy, Django solves the same problems inherent...