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.


Labels:

Comments

Post a Comment

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...
Post a Comment
Read more

My Story: A Mommy Start To Learn Code From Zero

From Google Image I am not a programmer, and I thought I would never become one. Everytime I see someone is coding, I think he or she must be very talent.  For me, coding is a very difficult subject to learn. Not only the language has so many rules, but also the logical reasoning behind the language is complex.  In my graduated school, I knew many friends who didn't have any coding background, but they are doing programmer or developer jobs now. Some of them went to school to study coding, and some of them  learned to code by themselves. Their stories are so impressive.  I wasn't ready to learn code until I finished my first Chinese book "留学，我的青春呀!" recently. I always want to be a writer and write my own book. I started writing blog three years ago, and I updated my post two to three times every week. As I enjoyed writing , I started to get some followers, likes, and good comments on my blog. Then, I decided to plan my first book. My First...
Post a Comment
Read more

Three Most Common HTML Form Elements You Should Know

When I visited the Facebook page at the first time, it required me to sign up. Therefore, I completed the sign up form to create my new account. The form is very simple to fill in because it only asks for very common information such as full name, phone number, new password, birthday, and gender. It only took me one or two minutes to finish the form. Not only Social media sites require us to sign up first before we post anything, but many business or eCommerce sites also ask us to create new account before we take any action. For example, when I go to the Origins skin care site, it will pop up a email sign up form window. To encourage new customers to sign up, it gives a 15% off for the first order. It is definitely an attractive call-to-action message. Anyway, if your website requires users to sign up, you need to know how to create a HTML form. Yesterday, I just learned how to build a simple HTML form from Udemy course. And it is not that hard. All you need to kno...
Post a Comment
Read more