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Migrate from MongoDB to Postgres

Move your application from MongoDB to Postgres — convert document schemas to relational tables, rewrite queries to use a Postgres client, and migrate your data.
AuthorCognition
CategoryMigrations
FeaturesPlaybooks
1

Design the Postgres schema

Analyze your MongoDB collections and design relational equivalents. If your data involves multiple collections with relationships, create an Entity-Relationship Diagram first to validate normalization decisions before writing any SQL.Key translation patterns:
  • Document IDs: Convert MongoDB _id fields to UUID or SERIAL primary keys
  • Nested objects: Flatten into separate tables with foreign key relationships
  • Arrays: Use Postgres array types or separate junction tables
  • Embedded documents: Extract into related tables with proper normalization
Once the schema is ready, set up security: create Postgres roles with appropriate privileges, and enable Row Level Security (RLS) policies on tables that need row-level access control.
2

Migrate backend queries and dependencies

Replace your MongoDB driver (e.g. mongoose, mongodb) with a Postgres client library — Prisma, Drizzle, TypeORM, or node-postgres depending on your stack. Update your environment config with DATABASE_URL or equivalent connection credentials.Query migration patterns:
  • Find operations → SQL SELECT queries or ORM .findMany() / .select()
  • Aggregation pipelines → JOINs, GROUP BY, subqueries, window functions
  • Updates → SQL UPDATE statements
  • Inserts → SQL INSERT or bulk insert methods
If your app uses custom JWT auth with a MongoDB user store, update the user lookup queries to use Postgres while keeping the same token generation and validation logic.
3

Update the frontend service layer

Update frontend services to handle any data shape changes from the migration — most commonly _id becoming id. Keep existing service method signatures so components don’t need changes.
  • Update authentication services if the auth flow changed
  • Adjust HTTP client request/response handling for new data shapes
  • Update route guards and resolvers if data fetching patterns changed
4

Migrate data and run end-to-end tests

Export your MongoDB data, transform it to match the Postgres schema, and import it.After import, run the full test suite against the Postgres backend. Verify all CRUD operations, authentication flows, and role-based access work correctly.
5

Deploy and optimize

Deploy with feature flags for gradual rollout. Keep the MongoDB instance as a fallback during the transition.Post-deploy checklist:
  • Add indexes for frequently queried columns
  • Use EXPLAIN ANALYZE to identify slow queries
  • Set up connection pooling (e.g. PgBouncer)
  • Monitor query performance and connection utilization
  • Document rollback procedures for critical issues
Once everything is stable and verified, decommission the MongoDB instance.
6

Make it repeatable with a playbook

If you need to run this migration pattern across multiple services or repositories, save it as a playbook so every session follows the same process. Below is an example playbook for a MongoDB to Postgres migration: