Skip to main content

Data Association Study Notes: Six Steps to Embedded Data


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 mongoose and connect to MongoDB inside the file. And, we need to make sure the MongoDB is running in another window.


Then, we define user and post schemas by giving each of them an object with related items. For user, we need to have email, and name. For post, we need to have post title and content. And then, we put each schema into a mongoose model.

Step Two: Test New User

We create a new user with name "Mary" and email "mary@nyu.edu". And then, we save the user data into the database. As we run the server, it shows the new user information with unique id. And we use the same way to create new post and test successful.



Step Three: Embed Data

In order to relate the user to post, we need to embed data. To do that, we need to have a post attribute inside the user. Inside the post attribute, we will have many posts. So, we need to add the post schema inside of an array. Therefore, we tell the mongoose we want it to be a list which is an array of posts.

We also need to move the post schema to the top, so Node can find the post variable first, then related to the user schema.


Step Four: Push post to a new user

We create another new user. Then, we push the posts to the new user which we defined: newUser.posts.push(). Then, we save the new user and new post.


As result, it shows the new user with new posts in the database. The post has an array which includes the post title and content.



Step Five: Retrieve the data

We can use user.findOne({}, function()) to retrieve the a particular data from database. In this case, we retrieve Lily's data, and we see all her information and post.


Step Six: Add new post 

We can also push the post to the same user inside the retrieve function and save the data. 


Once we run the server, it shows Lily has two posts in the post array.


Comments

Popular posts from this blog

Intermediate Express.js: How To Add Styles & Partials in EJS File?

So far, we only have simple HTML tags and ejs tags in each ejs file. Every template page has no style at all. And the basic HTML header and footer are also missing. Today, I learned how to add styles and partials in ejs file. Link Style Step One: Touch a Separate CSS file I create a new directory "Style" under the "EJSDemo" directory, then I add a new CSS file "app.css" inside "Style" folder. Step Two: Add app.use(express.static()) in the app.js I add app.use(express.static("style")) in the "app.js". This will tell Express.js to serve the content of "Style" directory. Step Three: Write styles in CSS file I simple give body an orange background color and set text color to be grey. Step Four: Link to CSS file in the EJS file I just add <link> tag to link the "app.css" file on the top of the h1 tag in each ejs template. As the result, when I run the app and...

Intro to Backend: Is Browser The Only Place To Send HTTP Request?

Today,  I begin to learn the second part of web develop course: backend. Frontend is the stuff that we can see and interactive with, such as HTML, CSS, and JS. We can type our code, style our page, or write some function to make interaction. However, backend is everything else. For example, we type Target web address in the Internet Browser. As we hit "enter", there are a few steps to go through: 1. The HTTP request is sent to a particular server's IP address. 2. The server figures out what to send us 3. It sends a HTTP response back to us Those process we are hard to see, and it happens in less than one second. The instructor said that the browser is not the only place to send the HTTP request, and there are so many choices out there. In this learning course, we are going to use Postman App . Postman allows us to make HTTP requests and viewer responses. It is really for developers to understand how things are working or debug something. In the P...

Intermediate CSS: Three Steps To Create A Photo Gallery

I have seen many image blogs these years. People love to post their photos online to express life and feeling.  Image is powerful because it could bring a visual story to audience. People can see what you see, and may be feel the same way as you feel, too. If we want to build our own photo gallery, what should we do? Luckily, the boot-camp instructor just showed me how to use HTML and CSS to create a simple photo gallery.  I would love to share my study note here. (p.s. all the image links are provided by Udemy course instructor) Step One: Add Image Links on HTMLPage The instructor provides all the image links. All we need to do is add those links inside the <img> tag. Without CSS, the page will looks like this: they are not organized, and sizes are different, too. Step Two: Set Image Property Values We set the width of each photo the same value which is 30%, so there will be three images per line. The percentage value can help...