var userSchema = mongoose.schema({
  username: {type: String, unique: true, index:true, required: true},
  email: {type: String, unique: true, required: true},
  first_name: String,
  last_name: String,
  password: {type: String, required: true},
  role: {type: String, enum: ["admin", "user", "guest"], required: true},
  dob: Date,
  gender: {type: String, enum: ["male", "female"]},
  phone: String,
  profile_picture: String,
  created_on: Date,
  updated_on: Date
});