如何循环用户在所有列表中发布的类别

I am trying to display all of the categories a user on my site has posted in. This is how my models are set up: A user is able to create many listings. This is a one to many relation. A listing is able to have multiple categories, and categories have multiple listings (there are multiple listings with the same category). How do I show all categories a user has listed? I have tried I am trying to display all of the categories a