Problem:

I have three posts types: Customers, Appointments, Checklists.

Customers relates one to many with Appointments and Appointments relates one to one with Checklists.

I am trying to create an interface that allows to find the Customer, see past Appointments and Checklists and create a new Appointment

Solution:

The workflow should like below:

1) In the single "Customer" post, you can display one child post form link for creating child "Appointment" post,

2) after user submit the post form, redirect him to single "Appointment" post,

3) Same as above, in the single "Appointment" post, display another child post form link for creating grand-child "Checklist" post

Relevant Documentation:

https://toolset.com/course-lesson/selecting-parent-posts-when-using-forms-to-create-child-items/