Creating sub-module in MongoDB while loading test data from json file - node.js

Question

I am trying to load default data into my MongoDB database from a node.js backend.
This is the data I am loading as JSON:
[
{
"datetime": "28/08/2021 16:01:00",
"sensor": {
"id": 1,
"type": "Temperature"
},
"value": 2502
},
{
"datetime": "28/08/2021 16:02:00",
"sensor": {
"id": 2,
"type": "Temperature"
},
"value": 2252
}
]
And these are the mongoose models:
const SensorType = Object.freeze({
Temperature: "Temperature"
});
const SensorSchema = new mongoose.Schema({
id: { type: Number, required: true },
type: { type: Object.values(SensorType), required: true },
});
Object.assign(SensorSchema.statics, { SensorType });
const Sensor = mongoose.model('Sensor', SensorSchema);
const DataEntrySchema = new mongoose.Schema({
datetime: { type: String, required: true },
sensor: { type: SensorSchema, required: true },
value: { type: Number, required: true }
});
const DataEntry = mongoose.model('DataEntry', DataEntrySchema);
Loading the DataEntries like this:
mongoose.connect("mongodb://127.0.0.1:27017/",{
useCreateIndex:true,
useNewUrlParser: true,
useUnifiedTopology: true}
).then(() => {
console.log('Database Successfully Connected')
if(fill_default_data) {
DataEntry.create(
JSON.parse(fs.readFileSync(path.resolve(__dirname, 'test_data.json'), 'utf8'))
);
}
}, error => {
console.log(error)
}
);
However, I am noticing that no Sensor-objects are created inside MongoDB, only DataEntries - why is that? And how can I create Sensor-objects as well?
Of course, a DataEntry object has the sensor attached but if I call Sensor.find().then( sensors => res.json(sensors) ) an empty array is returned.

Answer 1

You probably can't use a schema in another schema. You need to use refs instead.
So something like this sensor: { type: SensorSchema, required: true } won't work.
You should replace it with sensor: { type: number, required: true, ref: 'Sensor' },, where the ref is the name of the model you want to refer to as a string. Notice that the type is a number as you want to pass the id of the relevant SensorDocument in the DataEntryDocument.
Moreover id is a virtual, you should use _id instead when you want to spec out ids in mongoose schemes.
So your mongoose schemes should look like:
const SensorSchema = new mongoose.Schema({
_id: { type: mongoose.Schema.Types.Number, required: true },
type: { type: mongoose.Schema.Types.String, required: true },
});
const Sensor = mongoose.model('Sensor', SensorSchema);
const DataEntrySchema = new mongoose.Schema({
datetime: { type: mongoose.Schema.Types.String, required: true },
sensor: { type: mongoose.Schema.Types.Number, ref: 'Sensor', required: true },
value: { type: mongoose.Schema.Types.Number, required: true }
});
const DataEntry = mongoose.model('DataEntry', DataEntrySchema);
I still don't know why the Object.freeze and Object.assign are here.
Now if you want a DataEntry, you first need to create a Sensor.
const sensor = new Sensor({ _id: 0, type: 'Temperature' })
await sensor.save()
const dataEntry = new DataEntry({ sensor: 0, datetime: 'some timestamp as string', value: 25 })
await dataEntry.save()
I am leaving the validation-specific logic out as it is out of the scope of this query.
You can checkout docs for mongoose populate for more information.