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Let's look at how we are going to model our data for this application.

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The most difficult part when it comes to building applications as a Fullstack developer or as a back

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end developer is how the data is going to be modular.

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That is based on my experience.

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So let's have a look at the logic behind the data flow.

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We are going to build a block application.

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So for block application, first step is we need to ask ourselves what are the users, who is going

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to use our application and what kind of data that we need.

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So let's look at the data flow.

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First one is we need users to use the application and for users we're going to have two types or three

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types based on your business logic.

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One is we can have the admin and then the super admin or any normal user, but for our case we are going

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to have two categories of users.

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One is authenticated user and then normal user.

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When we say authenticated, meaning that a user who has logged in and then the person can create and

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then delete a post.

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But for a normal user, the person can only view the post.

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So the next entity or data that we need to handle is what we call post, because the entire logic about

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application is about creating posts.

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The next concept is what we call comment because a user can comment on your post.

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So we need to have a separate entity or data for comment.

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And lastly, we are going to have what is called categories.

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These entities is what we call model and mongoose.

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So let's say how these models or entities or data are related.

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And this is what we call database relationship, meaning how comment is being related to post and how

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post is being related to categories, users and comment.

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And for Mongoose, we have different types of database relationship.

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One is called 1 to 1 relationship, one to many or many to many relationships.

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So let's see how these models are going to relate to each other.

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First step is let's focus on the users and then the post.

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Is it going to be 1 to 1 or one to many or many to many?

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In this case, it's going to be one to many relationships, meaning that a user can create many posts.

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So if a user view my profile or if I view my profile, I'll be able to see all the posts that I have

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created.

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The next one going to be the users and then the comment.

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Again, a user can create many comments.

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So in this case it's going to be one to many relationships.

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A user can create many comments, but one comment belongs to a single user.

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You can see that this one represents this user and then the red represents this one as well.

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So this show is that a comment belongs to a single user and for post and then the user is like I said,

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is going to be one to many relationships.

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So if I view a single post or be able to see a single user who created that post, I won't be able to

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see two or more users who has created a single post.

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The next one going to be the users and category for this one to a user can create many categories,

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but one category belongs to a single user.

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So this is what we call one to many relationship.

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So let's look at the comments and posts.

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What kind of relationship are you going to use?

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Definitely is going to be one to many relationships, meaning that a single post can have many comments,

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but one comment belongs to a single post.

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So what about post?

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And then the category is going to be 1 to 1 relationship, or it can be one to many relationships,

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meaning that a post can belongs to two or more categories, but ideally a post belongs to a single category.

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For this one, it's up to you.

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If you want a post to belong to two or more categories.

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So this is the flow.

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This is the relationship that we are going to use.

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Next is let's talk about how we are going to say the document into the model, for example, users and

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posts.

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For this one too, we have ways of doing it.

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When it comes to MongoDB, one is called using the embedded way, meaning that we are going to save

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the entire post into the user's field and this is what we call embedded, meaning we are using the entire

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post into the arrays of user field and we have the nest type and that is what you call by referencing

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meaning that instead of using the entire object, we are going to use only the idea of the post and

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save it into the user's field.

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And this is the recommended way of doing it that is using the reference way.

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Before we continue for our purpose, we are not going to create a separate model for categories, but

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instead we are going to create a field and then pass in the accepted categories.

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Well, as we proceed, all this concept will be clear to you.

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All right, Let's continue in the next video.