How to Fix Mongoose Cannot Overwrite Model Once Compiled Error

If you're using mongoose library with serverless framework, then you might have run to the following issue

Cannot overwrite YOUR_MODEL_NAME model once compiled.

As the error suggest this error occurs as a result of trying to override the same model again.

And you can actually fix it pretty easily.

Just assign the model only if it's not assigned already

Here's a quick example of how to do it.

const mongoose = require('mongoose');

const { Schema } = mongoose;
mongoose.Promise = global.Promise;

const customerSchema = new Schema(
    {
        name: {
            type: String,
            required: 'Please supply a name',
            trim: true
        },
        email: {
            type: String,
            unique: true,
            lowercase: true,
            trim: true,
            required: 'Please Supply an email address'
        }
    
    },
);

module.exports =
    mongoose.models.Customer || mongoose.model('Customer', customerSchema);