One very clever article showing all types of complicated relations that you may stumble upon in your job.
The author shows in a very clean way how to create such migrations, seeds and models.
Check out how morphs(), morphTo(), morphToMany(), morphedByMany and withPivot() are used.
Read it a couple of times, test it with all possible databases Laravel supports and see the differences, check the structure created: tables, data, foreign keys. Add, delete records and see what happens inside the database. Try creating your own app using these functions to get even more clear picture.
Laravel, Eloquent, polymorphism, one-to-many, many-to-many and polymorphic many-to-many relationships:
Defining relationships among database tables with Eloquent.
