Getting layer last modified value with QGIS Expression

Question

I am working on some revision tracking and would like to present information about when layers saved in a GeoPackage were last edited using an expression. I can create a custom function if necessary.

I have had a look in the QGIS Python API but can't find anything. Is there a way to find when a layer was last edited?

Answer 1

For now, I can only suggest Python solutions that can be turned into a custom function via the Function Editor.

So, there is a polygon layer called 'polygon', which was the last modified on: 2024-12-03 09:31:33

There are several of them:

1. Through the getmtime() function from the os.path Python module:

   Return the time of last modification of path. The return value is a floating-point number giving the number of seconds since the epoch (see the time module). Raise OSError if the file does not exist or is inaccessible.

   # imports
   from os.path import isfile, getmtime
   from datetime import datetime
   from qgis.core import QgsProject
   
   # getting the vector layer by its name
   layer = QgsProject.instance().mapLayersByName("polygon")[0]
   
   # getting the file path of the data source
   source_path = layer.dataProvider().dataSourceUri().split('|')[0]
   
   # checking if the source is a file and get its last modified time
   if isfile(source_path):
       # getting the last modified time using getmtime
       modified_time = getmtime(source_path)
       # formating the timestamp for readability
       formatted_time = datetime.fromtimestamp(modified_time).strftime('%A, %d. %B %Y %H:%M:%S')
       print(f"Last modified: {formatted_time}")
   else:
       print("The layer source is not a file or its modification date cannot be determined.")
   

2. Utilizing the st_mtime() function from the os Python module:

   Get the status of a file or a file descriptor. Perform the equivalent of a stat() system call on the given path. path may be specified as either a string or bytes – directly or indirectly through the PathLike interface – or as an open file descriptor. Return a stat_result object.

   # imports
   from os import stat 
   from os.path import isfile
   from datetime import datetime
   from qgis.core import QgsProject
   
   # getting the vector layer by its name
   layer = QgsProject.instance().mapLayersByName("polygon")[0]
   
   # getting the file path of the data source
   source_path = layer.dataProvider().dataSourceUri().split('|')[0]
   
   # checking if the source is a file and get its last modified time
   if isfile(source_path):
       # using os.stat to get file metadata
       file_stats = stat(source_path)
       # getting the last modified time using st_mtime
       modified_time = file_stats.st_mtime
       # formating the timestamp for readability
       formatted_time = datetime.fromtimestamp(modified_time).strftime('%A, %d. %B %Y %H:%M:%S')
       print(f"Last modified: {formatted_time}")
   else:
       print("The layer source is not a file or its modification date cannot be determined.")
   

The output is: Last modified: Tuesday, 03. December 2024 09:31:33

3. As @J.R mentioned in their comment, information about the last modification could be data-type dependent, see for example Vector Drivers for more details. So, when one uses the ogr module, it could provide you with the DBF_DATE_LAST_UPDATE parameter for a shapefile:

   DBF_DATE_LAST_UPDATE=YYYY-MM-DD: Modification date to write in DBF header with year-month-day format. If not specified, current date is used.

   # imports
   from qgis.core import QgsProject
   from datetime import datetime
   from osgeo import ogr
   
   # getting the vector layer by its name
   layer = QgsProject.instance().mapLayersByName("polygon")[0]
   
   # getting the file path of the data source
   source_path = layer.dataProvider().dataSourceUri().split('|')[0]
   
   # openning the vector layer with ogr module
   dataSource = ogr.Open(source_path)
   daLayer = dataSource.GetLayer(0)
   
   # getting the last modified time
   modified_time = daLayer.GetMetadata_Dict().get('DBF_DATE_LAST_UPDATE')
   
   print(f"Last modified: {modified_time}")
   

The output is: Last modified: 2024-12-03.