Video Transcripts (English)

As a first step toward modeling relationships between entities in our bookstore app, let’s examine different types of relationships.

In this video, you'll learn how to identify three basic types of relationships: one-to-one, one-to-many, and many-to-many.

We’ll use the following questions to identify the relationship between two entities: can entity A be related to more than one entity B, and can entity B be related to more than one entity A.

Let’s apply these questions to Publisher and Headquarters entities.

You may remember that when we established entities in a previous unit, we included headquarters as an attribute of the publisher entity.

Let’s assume, now, that headquarters actually exists as its own entity in our app.

Can a publisher have more than one headquarters and can a headquarters have more than one publisher?

In our example, the answer to both of these questions is no. A publisher can only have one headquarters and a headquarters can only belong to one publisher.

We call this relationship one-to-one.

Next, let’s examine the relationship between printed books and review entities.

One book can have multiple reviews.

On the other hand, a single review can only be related to one book.

We call this relationship one-to-many.

To introduce the final relationship, let’s review Printed Books and Authors entities.

A book can have multiple authors and an author could have written more than one book.

This is a many-to-many relationship.

Nicely done. In this video we covered the following types of relationships: one-to-one, one-to-many, and many-to-many.

We also learned a set of questions to help us identify the relationship between two entities: can entity A be related to more than one entity B, and can entity B be related to more than one entity A.

In the next video, we’ll take a look at one of MongoDB’s super powers: Embedding vs referencing.