MissingSchemaError while using Mongoose Populate with only one model - mongodb

Question

**I have answered below. In short you need to require the Model in the module in which you wish to populate, even though you do not refer to it directly.
I am hitting a strange problem with mongoose when populating just one particular array of IDs.
I have three models, User, Company and Widgets.
When I return the company populated with the users all is fine using:
Company.findOne({ name: 'xyz' })
.populate('users')
.exec(function(err, company) {
if (err) return res.send(err)
res.send(company)
})
However when I try to replace populate 'users' with 'widgets' I get the following error:
{
"message": "Schema hasn't been registered for model \"widget\".\nUse mongoose.model(name, schema)",
"name": "MissingSchemaError"
}
Here are the models:
USER:
const UserSchema = new Schema({
name: String,
email: {
type: String,
unique: true,
required: true
},
password: {
type: String,
required: true
},
company: {
type: Schema.Types.ObjectId,
ref: 'company'
}
});
const User = mongoose.model("user", UserSchema);
COMPANY:
const CompanySchema = new Schema({
name: String,
URL: {
type: String,
unique: true
},
users: [{
type: Schema.Types.ObjectId,
ref: 'user'
}],
widgets: [{
type: Schema.Types.ObjectId,
ref: 'widget'
}]
});
const Company = mongoose.model('company', CompanySchema);
WIDGET:
const WidgetSchema = new Schema({
title: {
type: String,
required: true
},
maker: String
});
const Widget = mongoose.model('widget', WidgetSchema);
I have manually inspected the _ids in the widget array of the company model and they are all correct.

Answer 1

OK, so this was a lack of understanding on my behalf.
In the module where I was using:
Company.findOne({ name: 'xyz' })
.populate('users')
.exec(function(err, company) {
if (err) return res.send(err)
res.send(company)
})
I had imported the User model for other uses in the module. However, as I was not directly referring to Widget I had not imported it. Having done some more research I found that you need to import a model when populating even though not referring to it directly.
Let me know if best to delete whole thread or leave for reference.