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MongoDB Relational Migrator - Simplifying PostgreSQL to MongoDB Migration

Selva June 20, 2026 0 Comments

Introduction

Migrating from relational databases to NoSQL databases has traditionally been a challenging task. Unlike relational databases that organize data into normalized tables, MongoDB follows a document-oriented model where related data is often embedded within a single document. This architectural difference makes migration more than a simple data transfer—it requires schema redesign.

To simplify this process, MongoDB provides Relational Migrator, a free graphical tool that analyzes relational schemas, recommends an optimized MongoDB document model, and assists with data migration.

In this article, we'll explore how to migrate a PostgreSQL database using MongoDB Relational Migrator and examine its intelligent schema mapping capabilities.

What is MongoDB Relational Migrator?

MongoDB Relational Migrator is a desktop application designed to simplify migrations from relational databases to MongoDB.

Instead of manually redesigning your schema, the tool automatically:

  • Connects to relational databases
  • Discovers tables and relationships
  • Analyzes foreign keys
  • Recommends an optimized MongoDB document model
  • Generates sample JSON documents
  • Performs migration into MongoDB

Supported source databases include:

  • PostgreSQL
  • MySQL
  • SQL Server
  • Oracle Database

Target database:

  • MongoDB Community
  • MongoDB Enterprise
  • MongoDB Atlas

Why Use MongoDB Relational Migrator?

Migrating manually usually involves:

  • Understanding hundreds of relationships
  • Redesigning normalized tables
  • Writing ETL scripts
  • Validating migrated data
  • Optimizing document structures

MongoDB Relational Migrator automates much of this work, allowing developers to focus on reviewing and refining the suggested document model rather than building it from scratch.

Demo Environment

For this demonstration, the following environment was used.

Component

Version

PostgreSQL

17

MongoDB

Community Edition

MongoDB Relational Migrator

1.16.2

Operating System

Windows 11

The sample PostgreSQL database contains:

  • Customers
  • Customer Addresses
  • Customer Profiles
  • Products
  • Orders
  • Order Items
  • Employees
  • Categories
  • JSONB columns
  • Arrays
  • Recursive tables
  • Partitioned tables
  • Table inheritance

This provides a realistic enterprise-style schema for evaluation.

Step 1: Connect to PostgreSQL

The first step is establishing a connection to the source PostgreSQL database.

Provide:

  • Host
  • Port
  • Database
  • Username
  • Password

After validating the credentials, Relational Migrator confirms a successful connection.

Screenshot

Step 2: Select Tables

Once connected, the tool discovers all available schemas and tables.

You can choose:

  • Manual Selection
  • Bulk Selection

For this demo, all application tables were selected.

Screenshot

Step 3: Generate the Initial MongoDB Schema

This is one of the most interesting parts of the migration.

Relational Migrator offers three options:

  • Match relational schema
  • Recommended MongoDB schema
  • Empty MongoDB schema

For this demo, we selected:

Start with a Recommended MongoDB Schema

The tool analyzes:

  • Primary Keys
  • Foreign Keys
  • Relationship Cardinality
  • Table Structure

It then recommends which tables should become:

  • Top-level collections
  • Embedded documents

For example:

Customers

│

├── Customer Addresses

├── Customer Profiles

└── Orders

instead of creating separate collections for every table.

Screenshot

Step 4: Pre-Migration Analysis

Before any migration begins, the tool performs a comprehensive assessment of the source database.

The analysis includes:

  • Migration readiness
  • Unsupported database features
  • Potential risks
  • Performance considerations
  • Data type compatibility

The dashboard provides an overall readiness score along with detailed recommendations.

This feature helps identify issues before the migration starts, reducing the likelihood of surprises during execution.

Screenshot

Step 5: Visual Mapping

One of the standout features of Relational Migrator is its visual mapping interface.

Instead of reading SQL scripts or ER diagrams, you can see how relational tables are transformed into MongoDB collections.

The interface displays:

  • Relational schema
  • MongoDB collections
  • Embedded relationships
  • Reference mappings

Developers can manually adjust the suggested mappings whenever required.

For example:

Customers

   │

   ├── CustomerProfile

   ├── CustomerAddresses

   └── Orders

becomes

customers

{

   profile:{},

   addresses:[ ],

   orders:[ ]

}

This visualization makes it easy to understand the resulting document model before migration.

Screenshot

Step 6: Review Generated JSON Documents

Another useful capability is the automatic generation of sample MongoDB documents.

The JSON preview allows developers to verify:

  • Nested objects
  • Embedded arrays
  • Field names
  • Data types
  • Collection structure

This helps validate the document model before any data is migrated.

Example:

{

   "_id": ObjectId(),

   "productName": "Laptop",

   "price": 45000,

   "attributes": {},

   "orderItems": [

      {

         "quantity": 2,

         "price": 45000

      }

   ]

}

This preview significantly reduces uncertainty during schema design.

Screenshot

Step 7: Configure MongoDB Destination

After reviewing the schema, configure the destination MongoDB server.

Provide:

  • Connection URI
  • Database
  • Authentication credentials

Once connected successfully, the migration destination is ready.

Screenshot

Step 8: Migration Options

MongoDB Relational Migrator supports multiple migration modes.

Available options include:

  • Snapshot Migration
  • Continuous Migration
  • Data Verification
  • Error Handling
  • Selective Collection Migration

Snapshot mode performs a one-time migration, while Continuous mode keeps MongoDB synchronized with ongoing changes in the relational database.

Screenshot

Step 9: Review Migration Summary

Before execution, the tool displays a migration summary.

This includes:

  • Migration mode
  • Number of tables
  • Rows to migrate
  • Data size
  • Target collections
  • Validation messages

This final review provides an opportunity to verify the migration plan before starting the actual data transfer.

Screenshot

Note: In this demonstration, we stop at the review stage to focus on schema discovery and document modeling. Production migrations may require additional schema refinement, particularly for complex many-to-many relationships and application-specific business logic.

Key Features

MongoDB Relational Migrator offers several capabilities that simplify relational-to-document migrations:

  • Automatic schema discovery
  • Intelligent document modeling
  • Embedded document recommendations
  • Visual mapping interface
  • JSON schema generation
  • Pre-migration compatibility analysis
  • Snapshot and continuous migration modes
  • Migration validation
  • Support for PostgreSQL, MySQL, SQL Server, and Oracle

Benefits

Organizations adopting MongoDB can benefit from:

  • Reduced migration effort
  • Faster modernization projects
  • Better document schema design
  • Visual relationship mapping
  • Lower migration risk
  • Easier validation before deployment
  • Improved understanding of MongoDB best practices

Best Practices

To achieve successful migrations:

  • Review the recommended document model before migrating.
  • Understand application query patterns when deciding between embedding and referencing.
  • Test migrations using a representative subset of production data.
  • Validate generated JSON documents before moving to production.
  • Review many-to-many relationships carefully, as they may require manual refinement.
  • Perform application-level testing after migration to ensure expected behavior.

Conclusion

MongoDB Relational Migrator significantly simplifies one of the most challenging aspects of database modernization: transforming normalized relational schemas into optimized MongoDB document models.

Its combination of automated schema discovery, visual mapping, pre-migration analysis, and JSON document generation helps developers understand how relational data can be represented in MongoDB before executing a migration.

While complex scenarios such as many-to-many relationships or advanced business logic may still require manual adjustments, the tool dramatically reduces the time and effort involved in planning and validating a migration.

For organizations considering a move from PostgreSQL, MySQL, SQL Server, or Oracle to MongoDB, MongoDB Relational Migrator is an excellent starting point for evaluating schema transformations and accelerating modernization initiatives.

 

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