TypeError: Cannot read property 'execPost' of undefined

[mrdulin]

Try to use the Query class to build a query.

import mongoose from 'mongoose';
import { config } from '../../config';

mongoose.set('debug', true);

const schema = new mongoose.Schema({
	name: String,
});
const User = mongoose.model('user', schema);

(async function main() {
	try {
		await mongoose.connect(config.MONGODB_URI);

		// test
		const query = new mongoose.Query();
		const r2 = await query
			.setOptions({ lean: true })
			// @ts-ignore
			.collection(User.collection)
			.where({ name: 'Tom Benzamin' })
			.select({ _id: 0, address: 0 })
			.exec();
		console.log('r2: ', r2);
	} catch (error) {
		console.error(error);
	} finally {
		await mongoose.connection.close();
	}
})();

Got a runtime error:

TypeError: Cannot read property 'execPost' of undefined
    at /home/lindu/workspace/mongoose-codelab/v7/node_modules/mongoose/lib/query.js:4440:28
    at new Promise (<anonymous>)
    at _executePostHooks (/home/lindu/workspace/mongoose-codelab/v7/node_modules/mongoose/lib/query.js:4437:10)
    at Query.exec (/home/lindu/workspace/mongoose-codelab/v7/node_modules/mongoose/lib/query.js:4409:15)
    at processTicksAndRejections (internal/process/task_queues.js:95:5)
    at async main (/home/lindu/workspace/mongoose-codelab/v7/stackoverflow/53437031/index.ts:20:14)

The code line that throws this error is here

function _executePostHooks(query, res, error, op) {
  return new Promise((resolve, reject) => {
    const opts = error ? { error } : {};

    query._queryMiddleware.execPost(op || query.op, query, [res], opts, (error, res) => {
      if (error) {
        return reject(error);
      }

      resolve(res);
    });
  });
}

Why query._queryMiddleware is undefined? Did I build the query correctly? There is no post middleware in my code.

[vkarpov15]

We will improve this error message, but the general idea is that you're not supposed to instantiate the Query class directly. From the Query API docs:

Why are you using this pattern to create queries rather than using models?

[mrdulin]

Yeah, I know it's recommended to use the static methods of the Model. Shouldn't these two ways be equivalent? Model.find() is equivalent to new mongoose.Query()? If instantiating the Query class directly is not recommended, why not make it private? Anyway, is this error caused by a bug?

[hasezoey]

Anyway, is this error caused by a bug?

no, the query is just not expected to execute without a model and operation being associated with it (the error does not directly happen at new because those can be set before being executed)

you should be able to do

new Query(undefined, undefined, MODEL, undefined);
// or
const query = new Query();
query.model = MODEL;

see

mongoose/lib/model.js

Lines 2077 to 2081 in 67b4224

	const mq = new this.Query({}, {}, this, this.$__collection);
	mq.select(projection);
	mq.setOptions(options);
	return mq.find(conditions);

also see #13571

[mrdulin]

I thought query.collection(User.collection) make an association with a model/collection.

[vkarpov15]

You can think of Query as an abstract class - the Query class methods are part of our documented API, but the constructor isn't, because we don't expect people to instantiate the Query class directly.