I have two entities which are in a parent/child relationship. Now I want to add a operations link in the parent's list view so that I can show the child's entity form with the reference to the parent pre-populated.
Ideally, the URL would look something like /admin/myparent/123/mychild/add, where 123 is the ID of the parent entity to which the new child should have a reference. I have the link in place in the operations menu, but I can't figure out how to have my ChildEntityForm load in the parent entity based on the URL parameter. How do I do this in Drupal 8?
I found a couple of questions regarding this here on SO, but they were all about Drupal 7. In addition, the documentation (Using parameters in routes) regarding upcasting url parameters states this:
Note that this method of providing the entity data to a form is not used for entity forms, such as forms to add/edit/delete entity data.
So is there a solution to this, preferably one that would not require installing a third-party module?