How to create a Content Type field that will be only set by query parameters? I'm using Drupal 7. I want to create an Entity Reference field in my Order content type that will be set based on whatever the query parameter node ID is for my parent node. In other words, the user is viewing a table list of parent nodes. The right-most column is a link to "File Order" (as in, create a child node relating to that particular parent node). So the URL that it links to is /node/add/order?nid=[nid of parent].

On the Order node add screen, the "Related Node ID" Entity Reference field should auto-populate based on whatever the nid query parameter is. So the user should not have to worry at all about setting that value ever. How do I do this?
The Prepopulate module appears to be what you're looking for.