Our own Drush command
So, our logic is in place, but we will need to create a handy way we can trigger the imports. One option is to create an administration form where we go and press a button. However, a more typical example is a command that can be added to the crontab and that can be run at specific intervals automatically. So that's what we are going to do now, and we will do so using Drush.
The Drush command we are going to write will take an optional parameter for the ID of the Importer configuration entity we want to process. This will allow the use of the command for more than just one importer. Alternatively, passing no options will process each importer (in case this is something we want to do later on). One thing to note is that we won't focus on performance in this example. This means the command will work just fine for smaller sets of data (as big as one request can process) but it would be better to use a queue and/or batch processing for larger sets. Also...