QR Codes

When working in my collection, it’s sometimes helpful to access a specimen’s record on my web app to view additional information not present on the label. Rather than have to type in the specimen’s unique identifier into the URL, I decided to generate QR codes to print alongside the labels that, when scanned with a smart phone, will take me directly to that specimen’s page on my site.

Creating the Short Codes

There is a read-only field on the SpecimenRecord model called short_code. This short_code is just the unique specimen identifier (usi) but without the letters and hyphen (so MEM-000001 becomes 000001). This short code is used to generate a shortened URL, as shorter URLs make it easier to generate a smaller QR code that is still scannable.

This field gets populated whenever a SpecimenRecord is saved. However, there are also a couple of management commands that can be run to generate the short codes (these really shouldn’t need to be used, except for the very first case of me implementing this feature and having some specimens without the short code).

To generate short codes for only specimens that lack them, run the following command:

make generate-short-codes

To generaet short codes for all specimens (whether or not they already have them), run the following command:

make generate-short-codes --all

Note

You’ll likely be running these commands in prod, rather than locally (though if your local database is just a copy of prod, you can run them locally instead and get the same results). To run the commands in prod, you’ll first have to run make fly-auth followed by make fly-run-command command="python manage.py generate_short_codes".

Exporting QR Codes for Printing

In the Wagtail admin, there’s a link in the main left navigation, “Export QR Codes” (/admin/export-qr-codes/). This takes you to a form where you can enter a range of specimens for which you want to generate QR codes. Submitting the form generates a PDF with the QR codes that’s downloaded to your machine. If you don’t provide a range of specimens, then QR codes are generated for all specimens in the database.

How the QR Codes Work

Because I needed the QR codes to be small enough to fit on a specimen label, I needed to shorten the URLs encoded while still taking the user to the correct specimen page on the frontend when scanned. The URLs encoded in the QR codes are in the following format: www.memcollection.com/s/{short_code}. Navigating to a URL like this will redirect the user to the corresponding URL: https://www.memcollection.com/specimens/{full_usi}.

The actual redirect lives in a .htaccess file within the Eleventy frontend. Because it’s just a static file hosted alongside my frontend, if my backend server were to go down, the QR codes will still work (so long as my frontend remains live!).