Filling out field with matching between existing field value and file name in QGIS

Question

I need to fill out new fields using "Field Calculator" in QGIS.

What do I need to load in those fields?

URL's containing the path to a image file (we can use the statement 'base_file_name'). The thing gets complicated when I'm talking about thousands of records (so I cannot copy and paste every single path into the field, I need to make it automatically during a Graphic Modeler processing).

The drop that spilled the glass is that I need that the fields should be filled out with a matching using an existing field in the Shapefile containing a string with a long text (example: "bf5ae62b-a7c9-4682-9c20-4c457de38a9b") and using this code to match it with a file within a folder (each image file name contains this code, for example: bf5ae62b-a7c9-4682-9c20-4c457de38a9b.jpg). I need to find an expression to make it possible and load all the URL at once using this criteria.

Answer 1

Here's a description of what I do in what seems to be an analogous situation.

I have a layer, Photos, which has a "SourceFile" field that has the fully qualified filename of jpegs. I periodically update it with another layer, NewObservations which has a field, "Identifier". Entries from NewObservations get pasted into Photos and then using field calculator I update the "SourceFile" field to:

concat(@photo_directory,"Identifier",'.jpg')

In this case, @photo_directory is a layer-level variable with the directory of the photos, with trailing \ (Windows). I use a variable for portability.

By the way, I've done this both with "SourceFile" as an actual stored field, and as a virtual field defined in QGIS.