How to migrate from MySQL to MongoDB

Introduction

Migrating from a traditional relational database like MySQL to a NoSQL database such as MongoDB requires understanding the differences between the two and careful planning. The following tutorial will guide you through the process, step-by-step, from setting up the databases to transforming and importing your data.

Prerequisites

• MySQL installed with existing data
• MongoDB installed
• Understanding of relational and document-oriented data models
• Access to a terminal or command prompt

Step-by-Step Instructions

Step 1: Preparation and Planning

Begin by examining your existing MySQL schema to determine how to transform tables into MongoDB collections. Understand the relationships between tables and identify which ones can become embedded documents.

Step 2: Exporting Data from MySQL

Export your MySQL data into JSON or CSV using a command like:

SELECT * FROM table_name INTO OUTFILE '/path/to/file.csv' FIELDS TERMINATED BY ',' ENCLOSED BY '"' LINES TERMINATED BY '\n';

This will generate a CSV file for each table which you can then prepare for MongoDB.

Step 3: Schema Transformation

Design your MongoDB schema by considering how to map relational concepts like foreign keys to MongoDB’s document references, or by deciding what data to embed.

Step 4: Data Transformation

Write scripts to transform your exported data into the format that Mongo expects. Here’s a basic Python script that might help:

import csv
import json

def convert(csv_file, json_file):
    with open(csv_file, 'r') as cf, open(json_file, 'w') as jf:
        reader = csv.DictReader(cf)
        json_list = []
        for row in reader:
            json_list.append(row)
        json.dump(json_list, jf)

convert('table_name.csv', 'table_name.json')

Step 5: Importing Data into MongoDB

Using the mongoimport tool, you can import the JSON files into MongoDB:

mongoimport --db newdbname --collection newcollection --file /path/to/table_name.json

Repeat for each table or collection. Once imported, check the data integrity and the relations between documents.

Advanced Data Transformation

For more complex transformations involving relationships, consider writing a custom migration script that loads data from the CSV, transforms it, and then inserts it into MongoDB.

Handling Complex Relationships

MongoDB handles relationships differently. If your MySQL data has a lot of joins, you may need to rethink your approach. Embed directly related data, and use references for less closely related data. Script examples for these operations can be complex and specific to your data.

Data Validation

After importing, validate your MongoDB collections for content and structure to ensure it matches your new schema design.

Optimization and Indexing

Optimize your new MongoDB setup by analyzing query patterns and setting up indexes:

db.collection.createIndex({"fieldname": 1})

This is critical for performance, especially on large datasets.

Tips and Tricks

Here are some additional tips to help with the migration:

• Test your migration with a subset of data first.
• Consider using third-party tools for larger migrations.
• Document your data mapping and transformation rules.
• Validate the consistency of data post-migration.

Conclusion

Migrating from MySQL to MongoDB is a multi-step process that involves careful planning and execution. By following this guide, taking care to properly transform your data to suit MongoDB’s architecture, and validating the data post-migration, you can successfully complete the transition.