How to insert documents into MongoDB collections

insertOne and insertMany

MongoDB provides two core insert methods. insertOne adds a single document and returns an object containing the auto-generated or provided insertedId. insertMany accepts an array of documents and returns the count and all inserted IDs. Both methods are asynchronous and should always be awaited.

// insertOne — returns { acknowledged: true, insertedId: ObjectId }
const result = await db.collection('products').insertOne({
  name: 'Mechanical Keyboard',
  price: 79.99,
  category: 'peripherals',
  inStock: true,
  createdAt: new Date()
})
console.log(result.insertedId) // ObjectId('...')

// insertMany — insert an array of documents
const res = await db.collection('products').insertMany([
  { name: 'Mouse', price: 29.99, inStock: true },
  { name: 'Monitor', price: 299.99, inStock: false }
])
console.log(res.insertedCount) // 2
console.log(res.insertedIds)   // { '0': ObjectId, '1': ObjectId }

Ordered vs unordered inserts

By default, insertMany runs in ordered mode — it stops at the first error and skips remaining documents. Pass { ordered: false } to continue inserting remaining documents even after a failure in one of them, maximizing successful writes in a batch.

await db.collection('events').insertMany(docs, { ordered: false })
// Partial success: check insertedCount vs docs.length

If you supply a duplicate _id, MongoDB throws error code 11000. Omit _id entirely to let MongoDB auto-generate an ObjectId. Insert operations do not validate document structure unless a JSON Schema validator is attached to the collection at the database level.