MongoDB $rename Operator

The $rename operator in MongoDB lets you change field names without altering the stored values. It’s useful for schema cleanup and consistent naming across collections, even for nested fields.

• Renames fields without affecting data.
• Supports nested fields via dot notation.
• Allows multiple renames in one update.

Features of $rename Operator

Here are some features of $rename operator:

• Schema Refactoring: Helps standardize and reorganize field names.
• Nested & Arrays: Works with embedded documents using dot notation, but does not directly rename fields inside array elements.
• Safe Behavior: No operation if the source field is missing, replaces the target if it exists

Syntax

{ $rename: { <oldField>: <newField>, <oldField2>: <newField2>, ... } }

• <oldField>: The current name of the field you want to rename.
• <newField>: The new name for the field.
• The new name must be different from the old name.
• For embedded or nested documents, we can use dot notation to refer to the field within the nested structure.

Examples of MongoDB $rename

Examples of how to use the $rename operator in MongoDB, using an Employee collection as a sample.

• Database: GeeksforGeeks 
• Collection: Employee 
• Document: Three documents that contain the details of the employees in the form of field-value pairs.

Example 1: Rename a Single Field

Renaming experienceYear field to experience in the employee’s document whose first name is Noah. 

db.Employee.updateOne(
   { "name.first": "Noah" },
   { $rename: { "experienceYear": "experience" } }
)

Output:

Example 2: Renaming a multiple field

Renaming the department field to unit in all the documents present in the Employee collection. 

db.Employee.updateMany(
   {},
   { $rename: { "department": "unit" } }
)

Output:

Example 3: Rename a Field in an Embedded Document

Renaming personalDetails.contactInfo to personalDetails.phoneNumber field in an embedded document of the employee whose name is Ethan. 

db.Employee.updateOne(
   { "name.first": "Ethan" },
   { $rename: { "personalDetails.contactInfo": "personalDetails.phoneNumber" } }
)

Output:

Example 4: Renaming a Non-Existent Field

If a field does not exist in the document, the $rename operation will not perform any action. However, we can add a field first and then rename it. Here’s how you can rename a middle name to middleName:

db.Employee.updateMany(
   { "name.middle": { $exists: false } },
   { $set: { "name.middle": "" } }
);
db.Employee.updateMany(
   {},
   { $rename: { "name.middle": "name.middleName" } }
)

Output:

Usage of MongoDB $rename Operator

Here are some usage of $rename operator:

• Schema evolution: When you need to change the name of a field during schema migration or when adapting to new application requirements.
• Field standardization: When renaming fields to standardize naming conventions across your collection.
• Refactoring database: If you're restructuring your database to improve data consistency or query efficiency.