This is the fourth article in a series of articles about the Batch API in Drupal. The Batch API is a system in Drupal that allows data to be processed in small chunks in order to prevent timeout errors or memory problems.
So far in this series we have looked at creating a batch process using a form, followed by creating a batch class so that batches can be run through Drush and then using the finished state to control batch processing. All of these articles go together to form a basis of batch processing in Drupal.
In this article we will look at bringing these concepts together to perform a task that is quite common on websites, processing Comma Separated Value or CSV files, which we will do using the Drupal Batch API.
Processing CSV data is very common on the web. Whilst it is quite common to integrate with an API it is sometimes simpler to just generate a CSV file of the data you need from one system and upload it into a form on a website. Most systems will allow you to export data as a CSV file of some kind, but it's also very easy to export a CSV from commonly used programs like Excel and Google Sheets.
Processing a CSV file in PHP is quite simple, but once you reach one hundred records you will find that PHP will start to throw errors due to timeouts or memory issues. The solution is to employ the Batch API to spread the load of that processing over a number of different requests.