Mongoose, Next.JS OverwriteModelError: Cannot overwrite model once compiled - node.js

Question

I am trying to integrate mongoose and apollo with Next.js
I wrote this wrapper around apollo server:
import mongoose from "mongoose"
const {logger} = require("../middleware/logger");
const connect = async () => {
logger.info("Connecting to DB...");
await mongoose
.connect(process.env.MONGO_URI, {
useNewUrlParser: true,
useFindAndModify: false,
useUnifiedTopology: true
}).then(() => logger.info(`Mongo running at ${process.env.MONGO_URI}`))
.catch(err => logger.error(err));
}
const connectDB = (handler) => async (req, res) => {
if (mongoose.connections[0].readyState !== 1) {
await connect();
}
return handler(req, res);
}
const db = mongoose.connection;
db.once('ready', () => logger.info(`Connected to mongo on ${process.env.MONGO_URI}`));
export default connectDB;
In this model in separate file:
const mongoose = require('mongoose');
const {Schema} = mongoose;
const CustomerSchema = new Schema({
name: {
type: String,
required: [true, 'Customer name is required'],
unique: true,
trim: true,
},
createdAt: {
type: Date,
default: Date.now
}
}, {
toJSON: {
transform: function (doc, ret) {
ret._id = ret._id.toString();
delete ret.__v
}
}
});
module.exports = mongoose.model('Customer', CustomerSchema);
My apollo server looks like this now:
import {ApolloServer, gql} from "apollo-server-micro";
import connectDB from "../../middleware/db-middleware";
const _Customer = require("../../db/models/Customer");
const typeDefs = gql`
type Customer {
id: ID!
name: String!
createdAt: String
}
type Query {
hello: String!
}
type NewCustomerResponse {
success: Boolean!
message: String
}
type Mutation {
addCustomer(name: String!): NewCustomerResponse!
}
`;
const resolvers = {
Mutation: {
addCustomer: async (parent, {name}, context, info) => {
await _Customer.create({name});
return {success: true, message: "Sample message"};
}
}
};
const apolloServer = new ApolloServer({
typeDefs,
resolvers,
context: () => ({}),
});
export default connectDB(apolloServer.createHandler({path: "/api/gql"}));
First run works ok, but when I modify anything, and next.js auto-recompiles source files, it throws this error:
OverwriteModelError: Cannot overwrite `Customer` model once compiled.
Does anyone knows what am I doing wrong and how to resolve this issue?