Using MongoDB with Mongoose — Nested Documents

To make MongoDB database manipulation easy, we can use the Mongoose NPM package to make working with MongoDB databases easier.

In this article, we’ll look at how to use Mongoose to manipulate our MongoDB database.

Modify Nested Documents

We can modify nested documents by accessing the path and then set the value for it.

For example, we can write:

async function run() {
  const mongoose = require('mongoose');
  const connection = mongoose.createConnection('mongodb://localhost:27017/test');
  const childSchema = new mongoose.Schema({ name: 'string' });
  const parentSchema = new mongoose.Schema({
    children: [childSchema],
    child: childSchema
  });
  const Child = await connection.model('Child', childSchema);
  const Parent = await connection.model('Parent', parentSchema);
  const parent = new Parent({ children: [{ name: 'Matt' }, { name: 'Sarah' }] })
  await parent.save();
  parent.children[0].name = 'Mary';
  await parent.save();
  console.log(parent);
}
run();

We get the children subarray’s first entry’s name property and set it to 'Mary' .

Then we call save on the parent to save everything.

We can also call the set method to do the same thing.

For example, we can write:

async function run() {
  const mongoose = require('mongoose');
  const connection = mongoose.createConnection('mongodb://localhost:27017/test');
  const childSchema = new mongoose.Schema({ name: 'string' });
  const parentSchema = new mongoose.Schema({
    children: [childSchema],
    child: childSchema
  });
  const Child = await connection.model('Child', childSchema);
  const Parent = await connection.model('Parent', parentSchema);
  const parent = new Parent({ children: [{ name: 'Matt' }, { name: 'Sarah' }] })
  await parent.save();
  parent.set({ children: [{ name: 'Mary' }] });
  await parent.save();
  console.log(parent);
}
run();

We replaced the children array with the given entry.

Then we save the parent and child entries with the save method.

Adding Subdocuments to Arrays

We can add subdocuments to arrays.

For example, we can write:

async function run() {
  const mongoose = require('mongoose');
  const connection = mongoose.createConnection('mongodb://localhost:27017/test');
  const childSchema = new mongoose.Schema({ name: 'string' });
  const parentSchema = new mongoose.Schema({
    children: [childSchema],
    child: childSchema
  });
  const Child = await connection.model('Child', childSchema);
  const Parent = await connection.model('Parent', parentSchema);
  const parent = new Parent({ children: [{ name: 'Matt' }, { name: 'Sarah' }] })
  parent.children.push({ name: 'Jane' });
  await parent.save();
  console.log(parent);
}
run();

We call push on the children array to append an entry to the children subarray.

Removing Subdocuments

To remove subdocuments, we can call the remove method.

For example, we can write:

async function run() {
  const mongoose = require('mongoose');
  const connection = mongoose.createConnection('mongodb://localhost:27017/test');
  const childSchema = new mongoose.Schema({ name: 'string' });
  const parentSchema = new mongoose.Schema({
    children: [childSchema],
    child: childSchema
  });
  const Child = await connection.model('Child', childSchema);
  const Parent = await connection.model('Parent', parentSchema);
  const parent = new Parent({ children: [{ name: 'Matt' }, { name: 'Sarah' }] })
  await parent.children[0].remove();
  await parent.save();
  console.log(parent);
}
run();

to remove a document from the children array.

To remove an object, we can call the remove method on the object:

async function run() {
  const mongoose = require('mongoose');
  const connection = mongoose.createConnection('mongodb://localhost:27017/test');
  const childSchema = new mongoose.Schema({ name: 'string' });
  const parentSchema = new mongoose.Schema({
    children: [childSchema],
    child: childSchema
  });
  const Child = await connection.model('Child', childSchema);
  const Parent = await connection.model('Parent', parentSchema);
  const parent = new Parent({ child: { name: 'Matt' } })
  await parent.child.remove();
  await parent.save();
  console.log(parent);
}
run();

Conclusion

We can work with nested MongoDB documents easily with Mongoose.