MongoDB Update Documents

To update documents in MongoDB you pass a filter to choose documents and an update document with operators like $set that describe the change. updateOne changes the first match, updateMany changes all matches.

updateOne with $set

$set changes or adds fields without touching the rest of the document.

db.products.updateOne(
  { name: "Honey" },
  { $set: { stock: 50, price: 12.65 } }
)

{
  acknowledged: true,
  insertedId: null,
  matchedCount: 1,
  modifiedCount: 1,
  upsertedCount: 0
}

updateMany with $inc

$inc adds to a number (use a negative value to subtract). Here every beverage gets 10 extra units of stock.

db.products.updateMany(
  { category: "Beverages" },
  { $inc: { stock: 10 } }
)

{ acknowledged: true, insertedId: null, matchedCount: 2, modifiedCount: 2, upsertedCount: 0 }

Array Operators: $push, $addToSet, $pull

$push appends to an array, $addToSet appends only if the value is missing, and $pull removes matching values.

db.products.updateOne({ name: "Green Tea" }, { $addToSet: { tags: "organic" } })
db.products.updateOne({ name: "Almonds" }, { $pull: { tags: "organic" } })
db.products.find({ tags: "organic" }, { _id: 0, name: 1, tags: 1 })

[
  { name: 'Basmati Rice', tags: [ 'organic' ] },
  { name: 'Green Tea', tags: [ 'organic' ] }
]

Other Update Operators

• $unset removes a field
• $rename renames a field
• $mul multiplies a number
• $min / $max update only if the new value is lower / higher
• $currentDate sets a field to the current date

Upsert and replaceOne

With upsert: true, MongoDB inserts a new document when nothing matches. replaceOne swaps the whole document (except _id) for a new one.

db.products.updateOne(
  { name: "Wheat Flour" },
  { $set: { category: "Grains", price: 8, stock: 200 } },
  { upsert: true }
)

{
  acknowledged: true,
  insertedId: ObjectId('6720a7a9c2b9e81d4f3a1b0b'),
  matchedCount: 0,
  modifiedCount: 0,
  upsertedCount: 1
}

Frequently asked questions

What is the difference between updateOne and replaceOne?

updateOne applies operators like $set to change specific fields. replaceOne replaces the entire document with the one you pass, removing any fields you leave out.

How do I update a nested field in MongoDB?

Use dot notation: { $set: { "address.city": "Lahore" } }. Setting address: {...} instead would replace the whole embedded document.

How do I update a specific element in an array?

Use the positional operator: filter on the element, then $set: { "items.$.qty": 5 }. For several elements use arrayFilters with $[name].