Handle duplicates with express.js

Question

So I am trying to create a login for the first time with express and react using Postgres. My user can be added to the database so I jumped into handling duplicates. I am using the findUserByEmail function to find my email and then, in my routes, calling that function before posting the email. I hope you guys can help me, I've been 1 week with this.

This is my queries.js where I :

const findUserByEmail = email => {
  return pool.query("SELECT * FROM users WHERE email = $1", [email]);
};

const createUser = (request, response) => {
  const date_created = new Date();
  const { username, email, password } = request.body;

  bcrypt.genSalt(saltRounds, function(err, salt) {
    bcrypt.hash(password, salt, function(err, hash) {
      pool.query(
        `INSERT INTO users (username, email, password, date_created) VALUES ($1, $2, $3, $4 )`,
        [username, email, hash, date_created],
        (error, results) => {
          // console.log("---------->", email);
          if (error) {
            throw error;
          }
          response.status(201).send(`User added with ID: ${results.insertId}`);
        }
      );
    });
  });
};

and this is my index.js:

// ...Other connection code

//Routes

app.get("/users", queries.getUsers);
app.get("/user/:id", queries.getUserById);

app.post("/signup/user", (req, res, next) => {
  console.log(req.body.email, "----------1");
  queries
    .findUserByEmail(req.body.email)
    .then(user => {
      console.log(user.rows.length);
      if (user.rows.length < 0) {
        res.status(400).send("this email is already in use");
      } else {
        console.log("Hello");
        queries.createUser;
      }
    })
    .catch(err => {
      console.log(err);
      res.status(500).send("Something went wrong");
    });
});

app.put("/user/:id", queries.updateUser);
app.delete("/user/:id", queries.deleteUser);

app.listen(port, () => {
  console.log(`App running on port ${port}.`);
});

Is not giving me an error, but when I submit a new user, keeps posting forever and does not change.

My post request worked till now without using the findUserByEmail.

Thanks for your help.

Answer 1

You have no guarantee that findUsersByEmail will find anything, even if there is a previous call, creating a user. The reason is that the query creating the user may not have returned yet.

You need database constraints to deal with this.

Put a unique constraint on the email field and handle duplicate exceptions correctly.