> ## Documentation Index
> Fetch the complete documentation index at: https://docs.usebracket.com/llms.txt
> Use this file to discover all available pages before exploring further.

# MongoDB primary keys

> How Bracket treats MongoDB primary keys

## Summary

Bracket uses MongoDB ObjectId values to uniquely map each document to the opposing data source. The user does not need to do any prep work to configure primary keys.

<Tip>If you would like to sync the MongoDB ObjectId to a field in the opposing data sources, just add the `_id` field to the field mapping. The `_id` field will be read-only in the opposing source.</Tip>