Error hashing password field mongodb

I am creating a user model for an app. My user schema is this:

const mongoose = require('mongoose');
const Schema =  mongoose.Schema;
const bcrypt = require('bcrypt-nodejs');
SALT_WORK_FACTOR = 10;

const userSchema = Schema({
  email:{type: String, required: true},
  encrypted_password:{type: String, required: true},
  reset_password_token:{type: String},
  reset_password_sent_at:{type: Date},
  sign_in_count:{type: Number},
  current_sign_in_at:{type: Date},
  last_sign_in_at:{type: Date},
  current_sign_in_ip:{type: String},
  last_sign_in_ip:{type: String},
  active:{type: Boolean},
  role_id:[{ type: Schema.Types.ObjectId, ref: 'roles' ,required: true}],
  create_date:{type: Date, default: Date.now},
});

This is my create method:

module.exports.insert = (user, callback) => {
  User.create(user,callback);
}

I add this function to hashing the password, but doesn't work:

User.pre('create', function(next) {
    var user = this;

    // only hash the password if it has been modified (or is new)
    if (!user.isModified('encrypted_password')) return next();

    // generate a salt
    bcrypt.genSalt(SALT_WORK_FACTOR, function(err, salt) {
        if (err) return next(err);

        // hash the password using our new salt
        bcrypt.hash(user.encrypted_password, salt, function(err, hash) {
            if (err) return next(err);

            // override the cleartext password with the hashed one
            user.encrypted_password = hash;
            next();
        });
    });
});

I get the error

User.pre is not a function.

How can I store a encrypted password using the create function to save the data.

Thanks in advance

via joselegit