In this URL: les-formateurs-du-digital.fr/?category=test
It seems okay with the legacy view to display some information from the test category and information from the CPT associated with this category.
First question: Can I use only one view to get information from the category and CPT, or do I need to create two views?
Second question: These URLs are not really clean. I need a URL like this: les-formateurs-du-digital.fr/test or les-formateurs-du-digital.fr/category/test or something similar.
First question: Can I use only one view to get information from the category and CPT, or do I need to create two views?
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It depends what information you would like to display and how.
Normally, For instance:
if you have a post type Book with taxonomy "Book Authors" and custom fields (Book Name, Book Status, Book Cover Image, Published Year).
Now, when you create a view to display post type Book, with this view you can display Books posts with attached taxonomy terms for "Book Authors" and custom fields (Book Name, Book Status, Book Cover Image, Published Year).
Second question: These URLs are not really clean. I need a URL like this: les-formateurs-du-digital.fr/test or les-formateurs-du-digital.fr/category/test or something similar.
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I'm afraid that this is not possible due to the nature of a WordPress Query and the Custom Query parameters added by Views that is eventually added to support parametric search as we need to pass the URL arguments to the Query so it returns the correct results.