Custom Views field

Now that we have seen how data is exposed to Views, we can start understanding the NodeViewsData handler I mentioned earlier (even if not quite everything) a bit better. But this also provides a good segue back to our Product entity type's views_data handler, where we can now see what the responsibility of getViewsData() is. It needs to return the definition for all of the tables and fields, as well as what they can do. Luckily for us, the base class already provides everything we need to turn our product data into Views fields, filters, sorts, arguments, and potentially relationships, all out of the box.

But let's say we want to add some more Views fields that make sense to us in the context of our product-related functionality. For example, each product has a source field that is populated by the Importer entity from its own source field. This is just to keep track of where they come from. So, we may want to create a Views field that simply renders...