What is Association? Association will allow us to have multiple pieces of data collections in our database that are related to one another. Just like a Facebook user can have multiple posts or images in his account. Three Types of Association One to One: One of entity that's related to one another entity. For example, one student has one unique student ID. One to Many: One entity that's related to many of other entity. For example, one student has multiple social media accounts. And those social media accounts only belong to this student. Many to Many: Many entity related to both ways. For example, one student can take many course, and one course has many students. Embedded Data In this example, we will do the "One to Many" type. We have user and post. We want one user to have multiple posts. Step One: Set up and define schema Firstly, we need to create a new file "embed,js", and npm install mongoose. Then, we require the mong...