Updating nested array subdocuments based on a field in the main document is a common task when working with MongoDB and Mongoose. Here’s a simple guide and example to help you accomplish this.
Plan
- Use
Model.updateMany()
orModel.findOneAndUpdate()
to update multiple or a single document. - Use an aggregation pipeline (
[{}]
) as the second argument to reference document fields. - Use the
$set
stage within the pipeline to update the nested array. - Use the
$$ROOT
variable to reference fields from the main document.
Example
Assume you have a User
model where each user has an array of posts
, and you want to set each post’s authorName
field based on the user’s name
field.
Here’s how you can do it:
const mongoose = require('mongoose');
const { Schema } = mongoose;
const postSchema = new Schema({
title: String,
content: String,
authorName: String, // This is what we want to update
});
const userSchema = new Schema({
name: String,
posts: [postSchema],
});
const User = mongoose.model('User', userSchema);
async function updatePostAuthorNames() {
await User.updateMany(
{}, // Update condition, {} means all documents
[
{
$set: {
posts: {
$map: {
input: "$posts",
as: "post",
in: {
$mergeObjects: [
"$$post",
{ authorName: "$name" } // Set authorName in each post to the user's name
]
}
}
}
}
}
]
);
}
updatePostAuthorNames().then(() => console.log('Update complete.'));
Explanation
- Define Schemas: Define the
postSchema
anduserSchema
. - Update Logic:
- Use
updateMany()
to update all user documents. - Use an aggregation pipeline to modify the documents.
- The
$set
stage updates theposts
array. - The
$map
operator iterates over theposts
array. - The
$mergeObjects
operator merges the original post object ($$post
) with a new object containing the updatedauthorName
set to the user’sname
.
- Use
Running the Update
To run the update function, simply call it:
updatePostAuthorNames().then(() => console.log('Update complete.'));
This script updates the authorName
for all posts based on their respective user’s name
.
Conclusion
Updating nested array subdocuments using a main document field value in MongoDB with Mongoose is straightforward with the right approach. Using aggregation pipelines and Mongoose’s powerful querying capabilities, you can efficiently perform these updates.