Why is mongoose not allowing me to find by $in on _id unless I have a schema wrapping another schema? - mongodb

Question

Please, if anyone can help explain the below situation. I've lost hours only to discover a working solution but it doesn't make sense why it needs to be implemented this way.
For some reason if I connect mongo over nodejs, using 1 mongoose schema, I cannot search via $in.
When I wrap that single schema in another schema, with no additional information $in returns a match.
Note: the command line works always. So it is something to do with the way the schema needs to be impelemnted.
I am new to mongoose so maybe there is something obvious i am missing but it does not make any sense. Any help appreciated.
thanks
creation of data in docker
Note there is only one record:
#!/bin/bash
set -e
mongo <<EOF
use ${MONGO_DB_NAME}
db.createCollection("persons")
db.persons.insert({"name": "CPU"})
EOF
schema.ts
import { Model, Schema, Document, Connection } from 'mongoose';
interface IPerson {
_id: string;
name: string;
};
type TSchemaPerson = Schema<IPerson>;
const SchemaPerson: TSchemaPerson = new Schema({
_id: String,
name: String
});
// ##########################################################################
// ODD BEHAVIOUR ?
// I have to wrap SchemaPerson inside SchemaPersons,
// even though its basically a duplication in order to get $in to return a result
// --------------------------------------------------------
// \/
const SchemaPersons: Schema<TSchemaPerson> = new Schema({SchemaPerson});
// ##########################################################################
const collectionName: string = 'Person';
export type TDocumentPerson = Model<Document & IPerson>;
export type TConnPersons = (con: Connection) => TDocumentPerson;
// ##########################################################################
// ODD BEHAVIOUR ?
// If I return SchemaPerson instead of SchemaPersons here then $in does not return a result --------
// \/
const ModelPersons: TConnPersons = con => con.model(collectionName, SchemaPersons);
// ##########################################################################
export default ModelPersons;
graphql - resolver.ts
const persons: QueryResolvers['persons'] = async (parent, args, context) => {
console.log('persons()');
const { dbConn }: IContext = context;
if (dbConn) {
const Person: TDocumentPerson = ModelPersons(dbConn);
let result;
let resultIn;
try {
result = await Person.find().exec();
console.log('result = ', result); // Result in both cases = [ { _id: 5f36e199ebd39f53b437834b, name: 'CPU' } ]
resultIn = await Person.find({
_id: {
$in: [new ObjectId('5f36e199ebd39f53b437834b')]
}
}).exec();
// ##########################################################################
// ODD BEHAVIOUR ?
// Result with SchemaPersons = [ { _id: 5f36e199ebd39f53b437834b, name: 'CPU' } ]
// Result with SchemaPerson = [ ]
console.log('resultIn = ', resultIn);
// ##########################################################################
} catch (err) {
console.log('err = ', err);
}
}
};
Note if I change the model to a collection then it does work. See below:
schema.ts - connecting as collection
import { Schema, Collection, Connection } from 'mongoose';
interface IPerson {
_id: string;
name: string;
};
type TSchemaPerson = Schema<IPerson>;
const SchemaPerson: TSchemaPerson = new Schema({
_id: String,
name: String
});
export type TCollectionPersons = Collection & IPerson;
export type TConnPersons = (con: Connection) => TCollectionPersons;
const CollectionPersons: TConnPersons = con => con.collection('persons', SchemaPerson)
export default CollectionPersons;
resolver.ts
const persons: TCollectionPersons = CollectionPersons(dbConn);
let result;
let resultIn;
let resultById
try {
result = await persons.find().toArray();
console.log('result = ', result);
// Result [ { _id: 5f36e199ebd39f53b437834b, name: 'CPU' } ]
resultIn = await persons.find({
_id: {
$in: [new ObjectId('5f36e199ebd39f53b437834b')]
}
}).toArray();
console.log('resultIn = ', resultIn);
// Result [ { _id: 5f36e199ebd39f53b437834b, name: 'CPU' } ]
// cannot use findById on collection.
// resultById = await persons.findById('5f36e199ebd39f53b437834b');
} catch (err) {
console.log('err = ', err);
}
}