MongoDB Update Operators

// $set — set field value (creates field if it doesn't exist)
db.users.updateOne(
  { email: "alice@example.com" },
  { $set: { age: 30, city: "Boston", "address.zip": "02101" } }
)

// $unset — remove a field from the document
db.users.updateOne(
  { email: "alice@example.com" },
  { $unset: { temporaryToken: "" } }
)

// $inc — increment (or decrement with negative value)
db.users.updateOne({ _id: ObjectId("...") }, { $inc: { loginCount: 1 } })
db.products.updateOne({ sku: "LAPTOP-001" }, { $inc: { stock: -1 } })

// $mul — multiply a field value
db.products.updateOne({ sku: "LAPTOP-001" }, { $mul: { price: 1.1 } })  // 10% price increase

// $rename — rename a field
db.users.updateMany({}, { $rename: { "fname": "firstName", "lname": "lastName" } })

// $min — update only if new value is less than current
db.scores.updateOne({ userId: "u1" }, { $min: { lowestScore: 45 } })

// $max — update only if new value is greater than current
db.scores.updateOne({ userId: "u1" }, { $max: { highScore: 98 } })

// $currentDate — set field to current date
db.users.updateOne(
  { email: "alice@example.com" },
  { $currentDate: { lastLogin: true, lastModified: { $type: "timestamp" } } }
)

// $push — append a value to an array
db.users.updateOne(
  { email: "alice@example.com" },
  { $push: { hobbies: "gaming" } }
)

// $push with $each — append multiple values
db.users.updateOne(
  { email: "alice@example.com" },
  { $push: { hobbies: { $each: ["cooking", "hiking"] } } }
)

// $push with $each, $slice, $sort — keep only last 5 sorted items
db.users.updateOne(
  { email: "alice@example.com" },
  {
    $push: {
      recentViews: {
        $each: [{ productId: "p1", viewedAt: new Date() }],
        $slice: -5,
        $sort: { viewedAt: -1 }
      }
    }
  }
)

// $pop — remove first (-1) or last (1) element
db.users.updateOne({ email: "alice@example.com" }, { $pop: { hobbies: 1 } })   // remove last
db.users.updateOne({ email: "alice@example.com" }, { $pop: { hobbies: -1 } })  // remove first

// $pull — remove all elements matching a condition
db.users.updateOne(
  { email: "alice@example.com" },
  { $pull: { hobbies: "gaming" } }
)
db.orders.updateOne(
  { _id: ObjectId("...") },
  { $pull: { items: { qty: { $lt: 1 } } } }
)

// $addToSet — add only if value doesn't already exist (no duplicates)
db.users.updateOne(
  { email: "alice@example.com" },
  { $addToSet: { tags: "verified" } }
)

// upsert: true — insert if no document matches the filter
db.pageViews.updateOne(
  { page: "/home" },
  { $inc: { views: 1 }, $setOnInsert: { createdAt: new Date() } },
  { upsert: true }
)

// arrayFilters — update specific elements in nested arrays
// Update the qty of a specific item in an order's items array
db.orders.updateOne(
  { _id: ObjectId("...") },
  { $set: { "items.$[item].qty": 5 } },
  { arrayFilters: [{ "item.productId": "LAPTOP-001" }] }
)

// Update all array elements matching a condition
db.students.updateMany(
  {},
  { $set: { "grades.$[g].passed": true } },
  { arrayFilters: [{ "g.score": { $gte: 60 } }] }
)

// Field operators:
// $set         — set field value
// $unset       — remove field
// $inc         — increment/decrement
// $mul         — multiply
// $rename      — rename field
// $min         — update if new value is smaller
// $max         — update if new value is larger
// $currentDate — set to current date/timestamp
// $setOnInsert — set only on upsert insert

// Array operators:
// $push        — append to array
// $pop         — remove first/last element
// $pull        — remove matching elements
// $pullAll     — remove all listed values
// $addToSet    — add if not already present
// $each        — modifier for $push/$addToSet
// $slice       — modifier to limit array size
// $sort        — modifier to sort array elements
// $position    — modifier to insert at position

// Positional operators:
// $            — first matching element
// $[]          — all elements
// $[identifier] — filtered elements (with arrayFilters)