WhatToWatch/server/models/user.js

const user = (sequelize, DataTypes) => {
  const User = sequelize.define('user', {
    username: {
      type: DataTypes.STRING,
    },
  });

  // User.associate = models => {
  // User.hasMany(models.PlexLibrary, {onDelete: 'CASCADE'});
  // User.hasMany(models.PlexSection, {onDelete: 'CASCADE'});
  // };

  User.findByLogin = async login => {
    let user = await User.findOne({
      where: {username: login},
    });

    if (!user) {
      user = await User.findOne({
        where: {email: login},
      });
    }

    return user;
  };

  return User;
};

export default user;