What is the relationship between fieldgroups and templates?

[jordanlev]

I'm attempting to write a module that will create some templates, fields, and pages upon installation. I found this helpful forum thread that shows the code: https://processwire.com/talk/topic/4921-how-to-create-template-file-using-api-under-a-module/ ... but I am curious what is the conceptual difference between fieldgroups and templates? Looking at the database of a basic install, I don't see any records in the fieldgroups table that are not also represented in the templates table. Is it possible to have fieldgroups that are not part of a template? If so, what are some use cases for this? If not, then why even have two distinct entities instead of combining them into 1?

Thanks!

[Martijn Geerts]

Several templates can have the same fieldgroup.

Say you build a site for a greengrocer, and you want to sell fruit. You want to have different templates for apples pears and oranges, but don't need different fields, then you could share 1 fieldgroup with the apples pears and oranges templates. This way you could search $pages->find('template=apples') and find only apples, but use the same logic for pears and oranges. It could  save you time & extra logic.

When you delete a template with the API, be sure to delete the fieldgroup to, if it is the last template that uses the fieldgroup.