Introduction to MongoDB $strLenBytes Operator

$strLenBytes is an aggregation operator in MongoDB that is used to calculate the number of bytes in a string. Its return value is an integer that represents the number of bytes in the string. When it is necessary to compare, sort, or limit the length of a string, the $strLenBytes operator can be used.

Syntax

The syntax of the $strLenBytes operator is as follows:

{ $strLenBytes: <expression> }

Where <expression> is an expression that represents a string. The expression can be a text string, a field, or an expression that returns a string.

Use Cases

The $strLenBytes operator can be used in many scenarios, such as:

• Comparing the length of strings;
• Sorting strings;
• Limiting the length of strings;
• Calculating the length of a string and adding it as a field to a document.

Examples

Sample Data

Assuming we have the following documents:

{ "_id": 1, "name": "Tom", "description": "This is a test." }
{ "_id": 2, "name": "Jack", "description": "This is another test." }

Example 1: Using $strLenBytes to calculate the length of a string

We can use the $strLenBytes operator to calculate the length of the string in the description field and add it as a new field to the document. The operation is as follows:

db.collection.aggregate([
  {
    $addFields: {
      descriptionLength: { $strLenBytes: "$description" }
    }
  }
])

After executing this aggregation operation, the result is as follows:

{ "_id": 1, "name": "Tom", "description": "This is a test.", "descriptionLength": 14 }
{ "_id": 2, "name": "Jack", "description": "This is another test.", "descriptionLength": 21 }

As we can see, the new field descriptionLength represents the length of the string in the description field.

Example 2: Using $strLenBytes to limit the length of a string

We can use the $strLenBytes operator to limit the length of the string in the description field and truncate it to a specified length. The operation is as follows:

db.collection.aggregate([
  {
    $addFields: {
      descriptionShort: {
        $substrBytes: [
          "$description",
          0,
          { $min: [{ $strLenBytes: "$description" }, 10] }
        ]
      }
    }
  }
])

After executing this aggregation operation, the result is as follows:

{ "_id": 1, "name": "Tom", "description": "This is a test.", "descriptionShort": "This is a " }
{ "_id": 2, "name": "Jack", "description": "This is another test.", "descriptionShort": "This is an" }

As we can see, the new field descriptionShort represents the string in the description field that has been truncated to the specified length.

Conclusion

The $strLenBytes operator can be used in the aggregation pipeline to calculate the number of bytes in a string. It can conveniently help us process strings, obtain their length, and use them for statistical, sorting, filtering, and other operations.

In summary, $strLenBytes operator is a very useful aggregation operator in MongoDB. It can conveniently handle strings and improve query efficiency for scenarios that require string length calculation, filtering, sorting, and other operations, making data processing simpler and more efficient.