MongoDB $toUpper Operator

Example 1 — Sample Data

Imagine three employees. Names are lowercase; departments use mixed case on purpose so we can see grouping later.

db.employees.insertMany([
  { _id: 1, name: "john doe", department: "engineering" },
  { _id: 2, name: "alice smith", department: "marketing" },
  { _id: 3, name: "bob jones", department: "Engineering" }
]);

How the Data Is Stored in MongoDB

After the insert, MongoDB keeps three documents in employees. Run find() to see them:

db.employees.find()

[
  { _id: 1, name: "john doe", department: "engineering" },
  { _id: 2, name: "alice smith", department: "marketing" },
  { _id: 3, name: "bob jones", department: "Engineering" }
]

Read each document like this:

How It Works

1. Insert once. insertMany adds three employee documents to employees.
2. Case is stored as written. engineering and Engineering are different strings until you normalize them.
3. find() shows the same shape. What you inserted is what you get back—ready for $toUpper next.

Example 2 — Uppercase a Field

Goal: add an upperName field that is the uppercase form of name, without changing the original.

db.employees.aggregate([
  {
    $addFields: {
      upperName: { $toUpper: "$name" }
    }
  }
]);

{
  _id: 1,
  name: "john doe",
  department: "engineering",
  upperName: "JOHN DOE"
}
{
  _id: 2,
  name: "alice smith",
  department: "marketing",
  upperName: "ALICE SMITH"
}
{
  _id: 3,
  name: "bob jones",
  department: "Engineering",
  upperName: "BOB JONES"
}

How It Works

1. Read the stored name. John’s document has name: "john doe" from Example 1.
2. Convert case. $toUpper: "$name" → "JOHN DOE".
3. Keep all fields. $addFields adds upperName; the original name stays unchanged.

Example 3 — Case-Insensitive Group

Same employees, but group by uppercase department so engineering and Engineering count as one team.

db.employees.aggregate([
  {
    $group: {
      _id: { $toUpper: "$department" },
      count: { $sum: 1 },
      employees: { $push: "$name" }
    }
  },
  { $sort: { count: -1 } }
]);

{
  _id: "ENGINEERING",
  count: 2,
  employees: ["john doe", "bob jones"]
}
{
  _id: "MARKETING",
  count: 1,
  employees: ["alice smith"]
}

How It Works

1. Same stored documents. Still using the three employees from Example 1.
2. Normalize the key. $toUpper turns both department spellings into "ENGINEERING".
3. Group and count. $group merges John and Bob under one bucket; Marketing stays alone.
4. Easy check. Engineering should show count: 2.