How to create a likes and comment system in PostgreSQL? - node.js

Question

Context: I'm in an apprenticeship at Openclassrooms.com (Web dev path), and I'm doing the last project: I have to create a social network website from scratch, for the front-end I must use a framework of my choice (Vue.js, React, Angular, Svelte...) and for the back-end I must use an SQL database (like MySQL, PostgreSQL, Oracle, SQLite...).
For the Front-end, I'm using Angular.
For the Back-end, I'm using Node.js + Express + Sequelize
For the Database, I chose PostgreSQL
I did almost all the routes for the signup, login, view all posts and do CRUD operations with a single post.
But I'm stuck with the post controller for the likes and comments.
In the previous project of my apprenticeship, I had to create the Back-end where I had to do almost the same thing the posts were without comments), at the exception that I used Mongoose to make CRUD operations in MongoDB
The user had this model:
const mongoose = require("mongoose");
const sauceSchema = mongoose.Schema({
userId: { type: String, required: true },
name: { type: String, required: true },
manufacturer: { type: String, required: true },
description: { type: String, required: true },
mainPepper: { type: String, required: true },
imageUrl: { type: String, required: true },
heat: { type: Number, required: true, minimum: 1, maximum: 10 },
likes: { type: Number, required: true },
dislikes: { type: Number, required: true },
usersLiked: { type: Array, required: true },
usersDisliked: { type: Array, required: true },
});
module.exports = mongoose.model("Sauce", sauceSchema);
So here's how the likes for the previous project with MongoDB + Mongoose worked:
When the user liked a post, the front-end would send the userId (string) of the person who liked + like (integer between -1 and 1) + post_id (string) to the back-end
We search for the post in the database, and if it's present in the database, then we'll manipulate the likes/dislikes
Switch case 1: the like = 1/-1 → is the like/dislike present in the array of usersLiked/usersDisliked?
If it is → we remove the userId from the usersLiked/usersDisliked
If not → we add the userId in the usersLiked/usersDisliked array
And the amount of likes/dislikes is the length of the array
case 2: the like = 0 (meaning the user removes the like/dislike of the post) → Is the userId present in the usersLiked array?
If it is → we remove the userId from the usersLiked
If not → we remove the userId from the usersDisiked
Here's the code btw:
const findIndexInArray = require("../utils/likeSauce-function");
exports.likeSauce = (req, res, next) => {
Sauce.findOne({
_id: req.params.id,
})
.then((sauce) => {
let userId = req.body.userId;
let numberOfLikes = sauce.likes;
let numberOfDislikes = sauce.dislikes;
let usersLikedArray = sauce.usersLiked;
let usersDislikedArray = sauce.usersDisliked;
let userLikedOrDisliked = req.body.like;
console.log("Valeur de likes dans B2D: ", userLikedOrDisliked);
switch (userLikedOrDisliked) {
case 1:
{
//Où on like
let indexFound = findIndexInArray(usersLikedArray, userId);
if (indexFound > -1) {
console.log(
"User ID: " +
userId +
" found in the usersLikedArray → Like cancelled"
);
usersLikedArray.splice(indexFound, 1);
} else {
console.log(
"User ID: " +
userId +
" has NOT been found in the array of userIDs → Like added"
);
usersLikedArray.push(userId);
}
numberOfLikes = usersLikedArray.length;
let sauceObject = {
...JSON.parse(JSON.stringify(sauce)),
usersLiked: usersLikedArray,
likes: numberOfLikes,
};
Sauce.updateOne({ _id: req.params.id }, {...sauceObject, _id: req.params.id })
.then(() =>
res
.status(200)
.json({ message: "Sauce Object SUCCESSFULLY modified !" })
)
.catch((error) => res.status(400).json({ error }));
break;
}
//
case -1:
{
//Où on like
let indexFound = findIndexInArray(usersDislikedArray, userId);
if (indexFound > -1) {
console.log(
"User ID: " +
userId +
" found in the usersLikedArray → Like cancelled"
);
usersDislikedArray.splice(indexFound, 1);
} else {
console.log(
"User ID: " +
userId +
" has NOT been found in the array of userIDs → Like added"
);
usersDislikedArray.push(userId);
}
numberOfDislikes = usersDislikedArray.length;
let sauceObject = {
...JSON.parse(JSON.stringify(sauce)),
usersDisliked: usersDislikedArray,
dislikes: numberOfDislikes,
};
Sauce.updateOne({ _id: req.params.id }, {...sauceObject, _id: req.params.id })
.then(() =>
res
.status(200)
.json({ message: "Sauce Object SUCCESSFULLY modified !" })
)
.catch((error) => res.status(400).json({ error }));
break;
}
case 0:
{
let index = findIndexInArray(usersLikedArray, userId);
if (index > -1) {
usersLikedArray.splice(index, 1);
numberOfLikes = usersLikedArray.length;
let sauceObject = {
...JSON.parse(JSON.stringify(sauce)),
usersLiked: usersLikedArray,
likes: numberOfLikes,
};
Sauce.updateOne({ _id: req.params.id }, {...sauceObject, _id: req.params.id })
.then(() =>
res.status(200).json({
message: "Sauce Object SUCCESSFULLY liked !",
})
)
.catch((error) => res.status(400).json({ error }));
} else {
index = findIndexInArray(usersDislikedArray, userId);
if (index > -1) {
usersDislikedArray.splice(index, 1);
numberOfDislikes = usersDislikedArray.length;
let sauceObject = {
...JSON.parse(JSON.stringify(sauce)),
usersDisliked: usersDislikedArray,
dislikes: numberOfDislikes,
};
Sauce.updateOne({ _id: req.params.id }, {...sauceObject, _id: req.params.id })
.then(() =>
res.status(200).json({
message: "Sauce Object SUCCESSFULLY disliked !",
})
)
.catch((error) => res.status(400).json({ error }));
}
}
break;
}
default: //Pas de likes/dislikes AJOUTÉS par défaut
break;
}
})
.catch((error) => {
console.log("Error while attempting to find the sauce: " + error);
res.status(404).json({ error });
});
};
So that's the algorithm with the likes/dislikes of a post with MongoDB + Mongoose,
It's a rather simple implementation...
But how do I implement the like/dislike feature with PostgreSQL + Sequelize?
At first, I thought that I had to add a likes attribute to the table post, but that's wrong, I actually had to create a table for the likes and comments
So for the likes table:
-1 like_id attribute as the primary key
-2 other attributes as foreign keys (user_id and post_id)
For the comments table:
-1 comment_id attribute as the primary key
-3 other attributes as foreign keys (user_id, post_id and like_id)
Here also are the Sequelize models for each feature:
module.exports = (sequelize, Sequelize) => {
const Like = sequelize.define("like", {
like_id: {
type: Sequelize.INTEGER,
allowNull: false,
unique: true,
autoIncrement: true,
primaryKey: true,
},
user_id: {
type: Sequelize.STRING,
allowNull: false,
// references: "user", //Nom de notre table
// referencesKey: "user_id", //L'attribut référencé de la PK ce cette table
},
post_id: {
type: Sequelize.STRING,
allowNull: false,
// references: "post", //Nom de notre table
// referencesKey: "post_id", //L'attribut référencé de la PK ce cette table
},
});
return Like;
};
module.exports = (sequelize, Sequelize) => {
const Comment = sequelize.define("comment", {
comment_id: {
type: Sequelize.INTEGER,
allowNull: false,
unique: true,
autoIncrement: true,
primaryKey: true,
},
user_id: {
type: Sequelize.INTEGER,
allowNull: false,
references: "user",
referencesKey: "user_id",
},
post_id: {
type: Sequelize.INTEGER,
allowNull: false,
references: "post",
referencesKey: "post_id",
},
likes_id: {
type: Sequelize.INTEGER,
allowNull: false,
references: "likes", //Nom de notre table
referencesKey: "likes_id",
},
});
return Comment;
};
For the controller, I just have no idea as to how to do it, I looked at some posts but nothing very satisfying, if anyone could enlighten me, even just by giving me a hint, I'd be very grateful.
Also, here's an Entity Relationship Diagram to show all the tables I created:

Answer 1

I try this with mongoose but i hope with sequelize you can adjust to fit your request. I hope this can help you if there's any problem you can fix this comment and let me know.
export const commentPost = async (req, res) => {
try {
const { id } = req.params;
const { comment } = req.body;
if (!mongoose.Types.ObjectId.isValid(id)) throw new Error(`No post with id: ${id}`);
const post = await PostMessage.findById(id);
if (!post) throw new Error(`No post found with id: ${id}`);
post.comments.push({ text: comment });
const updatedPost = await post.save();
res.json(updatedPost);
} catch (err) {
res.status(404).send(err.message);
}
}