Mongoose populate not working in javascript when Schema is ReadOnly

Mongoose populate not working in JavaScript when Schema is ReadOnly

If you are using Mongoose, a popular object data modeling (ODM) library for MongoDB and Node.js, you may have encountered an issue where the populate function does not work as expected when the schema is set to read-only. In this blog post, we will explore this problem and provide multiple solutions to resolve it.

Understanding the Issue

When the Mongoose schema is set to read-only, the populate function fails to populate the referenced fields. This can be frustrating, especially when you need to access related data from other collections.

Solution 1: Use the lean() Method

The lean() method in Mongoose allows you to retrieve plain JavaScript objects instead of Mongoose documents. By using this method, you can bypass the read-only schema limitation and still populate the referenced fields. Here’s an example:

const userSchema = new mongoose.Schema({
  name: String,
  posts: [{ type: mongoose.Schema.Types.ObjectId, ref: 'Post' }]
}, { read: 'nearest' });

const User = mongoose.model('User', userSchema);

User.findById(userId)
  .populate('posts')
  .lean()
  .exec((err, user) => {
    // Access the populated posts
    console.log(user.posts);
  });

Solution 2: Use the Model.populate() Method

If you prefer to keep the Mongoose schema as read-only, you can use the Model.populate() method instead of the populate() function. This method allows you to manually populate the referenced fields. Here’s an example:

const userSchema = new mongoose.Schema({
  name: String,
  posts: [{ type: mongoose.Schema.Types.ObjectId, ref: 'Post' }]
}, { read: 'nearest' });

const User = mongoose.model('User', userSchema);

User.findById(userId)
  .exec((err, user) => {
    User.populate(user, 'posts', (err, populatedUser) => {
      // Access the populated posts
      console.log(populatedUser.posts);
    });
  });

Conclusion

When working with a read-only Mongoose schema, the populate function may not work as expected. However, you can overcome this limitation by using the lean() method or the Model.populate() method. Choose the solution that best fits your requirements and enjoy seamless population of referenced fields in Mongoose.