MongoDB $strLenCP Operator

Example 1 — Sample Data

Imagine two titles: hello (ASCII) and café (accented). We save them in a collection named titles.

db.titles.insertMany([
  { _id: 1, text: "hello" },
  { _id: 2, text: "café" }
]);

How the Data Is Stored in MongoDB

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

db.titles.find()

[
  { _id: 1, text: "hello" },
  { _id: 2, text: "café" }
]

Read those documents like this:

"hello" → h e l l o → 5 code points

"café"  → c a f é   → 4 code points

Form rule example:
  max 10 characters → use $strLenCP, not $strLenBytes

How It Works

1. Insert once. insertMany adds two title documents to titles.
2. Strings stay as written. Accents are still single characters even if they use more bytes.
3. find() shows the same shape. What you inserted is what you get back—ready for $strLenCP next.

Example 2 — Measure Character Length

Goal: add a chars field with the code-point length of each text value.

db.titles.aggregate([
  {
    $addFields: {
      chars: { $strLenCP: "$text" }
    }
  }
]);

{ _id: 1, text: "hello", chars: 5 }
{ _id: 2, text: "café", chars: 4 }

How It Works

1. Read each string. MongoDB already has "hello" and "café" from Example 1.
2. Count code points. $strLenCP counts characters, not UTF-8 bytes.
3. ASCII is simple. "hello" → 5.
4. Accents count as one. "café" → 4, even though é uses 2 bytes in storage.

Example 3 — Characters vs Bytes

Same data, but also compute $strLenBytes so you can see when character count and byte length diverge.

db.titles.aggregate([
  {
    $addFields: {
      chars: { $strLenCP: "$text" },
      bytes: { $strLenBytes: "$text" }
    }
  }
]);

{ _id: 1, text: "hello", chars: 5, bytes: 5 }
{ _id: 2, text: "café", chars: 4, bytes: 5 }

How It Works

1. Same stored titles. Still using hello and café from Example 1.
2. Characters. $strLenCP reports what users count.
3. Bytes. $strLenBytes reports UTF-8 storage size.
4. Easy check. For café, chars = 4 but bytes = 5—pick the operator that matches your rule.