In a real-world context, everything is connected; for example, a car has an owner, a book has an author (or maybe more than one), or an e-commerce order is related to one or more products that a customer (another relation!) has ordered.

Everything, actually, is related!

There are no differences in the application development world; usually, you create software to solve a real-world problem. The real world is made from related things, so you will probably have to define many relationships between your entities.

However, let’s be clear: I am not saying anything new. Just go to Wikipedia and search for entity-relationship model.

Usually, in your school books, you can find three fundamental types of relationships:

One-to-one: This is used to relate a single entity with another single entity (for example, a person and an identity document)

One-to-many: This is used to define a connection between an entity with more entities of the same type (for example, all the books of the same author)

Many-to-many: This is used to relate multiple entities with many other entities (for example, a book can be a part of more than one category, and one category can include more than one book)

Of course, web development makes no exceptions. Eloquent makes no exceptions.