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mongoose 4.0.1: pre "update" middleware this object does not return model object

Fresh5 days ago
Mar 14, 20260 views
Confidence Score56%
56%

Problem

Hi, I've a problem with the newest version of Mongoose. I'm creating an API with Express and Mongoose 4.0.1, and I'm not sure if I'm doing anything wrong, but the fact is whenever I try to use the new `pre` update middleware the same way I use `pre` save middleware, `this` object does not return the object being updated, instead it returns the `Query` object. Example of what I'm trying to explain: [code block] [code block] This is what I get in `this` reference object within the middleware, and I don't know how it's useful to me. [code block] Looking at the source code, some of its properties are defined inside `Query` function defined in `./node_modules/mongoose/lib/query.js`: Is this something unexpected or I am doing anything wrong? It would be interesting to have a solution because I don't like the idea of validating within a middleware on object saving and being forced to run validations directly on controller when updating. The same thing happens with findOneAndUpdate `pre` middleware, but I don't expect it to return the exercise before finding it. In fact and in my honest opinion, I think it would be interesting that findAndUpdate and findOneAndUpdate pre middlewares triggered find(One) and update middlewares, in this order, instead of having its own middleware. Thanks in advance for your help.

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1 Fix

Canonical Fix
Unverified Fix
New Fix – Awaiting Verification

Update Mongoose Middleware to Use `updateOne` or `findOneAndUpdate` Correctly

Medium Risk

In Mongoose 4.0.1, the `pre` middleware for `update` and `findOneAndUpdate` operations does not provide the document being updated as `this`. Instead, it provides the `Query` object, which can lead to confusion when trying to validate or manipulate the document before the update. This behavior is by design, as Mongoose treats these operations differently compared to `save` operations.

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  1. 1

    Use `updateOne` or `findOneAndUpdate` with a separate `pre` middleware

    Instead of relying on the `pre` middleware for `update`, create a separate middleware for `findOneAndUpdate` or `updateOne` that allows you to access the document being updated using `find` before the update occurs.

    javascript
    const mongoose = require('mongoose');

const schema = new mongoose.Schema({ name: String });

schema.pre('findOneAndUpdate', async function(next) {
  const update = this.getUpdate();
  const doc = await this.model.findOne(this.getQuery());
  // Perform validation or manipulation on `doc` here
  next();
});

const Model = mongoose.model('Model', schema);
  2. 2

    Implement Validation Logic in Middleware

    Add your validation logic within the `pre` middleware to ensure that the document meets the required criteria before proceeding with the update. This allows you to keep your validation centralized and maintainable.

    javascript
    if (!doc) {
  return next(new Error('Document not found')); // Handle document not found
}
if (!update.name) {
  return next(new Error('Name is required')); // Example validation
}
  3. 3

    Test the Middleware Functionality

    Create unit tests to ensure that the middleware behaves as expected. Confirm that the validation logic correctly prevents updates when the criteria are not met.

    javascript
    const request = require('supertest');
const app = require('./app'); // Your Express app

describe('PUT /model/:id', () => {
  it('should return 400 if name is missing', async () => {
    const response = await request(app)
      .put('/model/123')
      .send({});
    expect(response.status).toBe(400);
  });
});
  4. 4

    Update Documentation and Code Comments

    Ensure that your code is well-documented, especially regarding the behavior of the `pre` middleware for `findOneAndUpdate` and `updateOne`. This will help future developers understand the design decisions and the need for separate handling.

    javascript
    // This middleware handles validation for updates, ensuring the document is valid before proceeding.

Validation

To confirm the fix worked, run your API tests to ensure that updates are validated correctly and that invalid updates are rejected with appropriate error messages. Additionally, check that valid updates proceed as expected.

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Environment

Submitted by

AC

Alex Chen

2450 rep

Tags

mongoosemongodbodmwon't-fix