Let's walk through the problems in your schema first—these are almost certainly causing your populate() failures:

1. Broken Nested Schema Structure #

You’re incorrectly using type: {} to define nested objects under social and requests. In Mongoose, nested fields don’t need an extra type wrapper—you can directly define their structure. This invalid syntax confuses Mongoose and prevents proper reference resolution for populate().

2. Typo in Date Default #

Date.Now() is a typo—it should be Date.now() (lowercase n). Using Now() will throw a reference error because that’s not a valid Date method.

3. Misplaced & Incomplete select Option #

Your select: fa... line is cut off and placed in the wrong spot. If you want to hide the requests field by default, the select: false should be a direct option of the requests object, not nested inside a type block.

4. Incomplete Schema Definition #

The requests section of your schema is truncated, which would cause Mongoose to fail initializing the model entirely.

Corrected User Schema #

Here’s the fixed version with all issues resolved:

const mongoose = require('mongoose');
const Schema = mongoose.Schema;

const UserSchema = new Schema({ 
  name: { type: String }, 
  location: { type: String }, 
  picture: { type: String }, 
  social: { 
    followers: { 
      type: [{ 
        user: { type: mongoose.Schema.Types.ObjectId, ref: 'User' }, 
        date: { type: Date, default: Date.now } // Fixed typo, no need for parentheses here
      }], 
      select: false // Kept default hidden, correct placement
    }, 
    requests: { 
      follow: [{ 
        user: { type: mongoose.Schema.Types.ObjectId, ref: 'User' }, 
        date: { type: Date, default: Date.now }
      }],
      select: false // Optional: hide requests by default
    } 
  }
});

module.exports = mongoose.model('User', UserSchema);

Proper populate() Usage #

Since you’ve set select: false on some fields, you need to explicitly include them in your query before populating:

Populate Followers

User.findById(yourUserId)
  .select('social.followers') // Explicitly include the hidden field
  .populate('social.followers.user') // Target the nested user reference
  .exec((err, user) => {
    if (err) throw err;
    console.log('Populated followers:', user.social.followers);
  });

Populate Follow Requests

User.findById(yourUserId)
  .select('social.requests.follow')
  .populate('social.requests.follow.user')
  .exec((err, user) => {
    if (err) throw err;
    console.log('Populated follow requests:', user.social.requests.follow);
  });

Quick Note #

If you already created a collection with the broken schema, you may need to drop the existing collection or migrate the data to match the new structure—Mongoose won’t automatically fix existing documents with invalid schema formatting.

内容的提问来源于stack exchange，提问作者Vivek