Every Rails application carries its history inside the database.
Tables evolve, columns change, and assumptions made two years ago suddenly don’t hold anymore. That’s why database migrations in Ruby on Rails deserve more than a quick rails db:migrate and crossed fingers.
If you’ve worked with Ruby on Rails long enough, you already know the truth:
database migrations will indeed go wrong at some point.
You can plan carefully, follow best practices, and test everything in staging and still hit a snag when a migration meets real-world data, production traffic, or an edge case no one anticipated.
That’s not a failure.
That’s just software development.
Over the years, while working on Rails migrations and Rails upgrades, we’ve seen a familiar set of issues come up again and again. The good news? Most of them are predictable and fixable, if you know what to look for.
Here’s a practical rundown of the most common Rails database migration problems, along with approaches that actually work in the real world.
1. Version Conflicts and Migration Collisions
When multiple developers are working in parallel, migration conflicts are almost inevitable. Two people generate migrations at the same time, both get the same timestamp, and suddenly Rails isn’t sure what comes first.
You’ll usually notice this through schema conflicts or migrations running out of order.
How to handle it:
Reorder the migrations logically and regenerate sequential numbers if needed. The key is to ensure migrations run in a deterministic order, especially before merging into main or deploying.
2. Schema Drift and Missing Elements
A migration fails halfway through. Someone fixes it locally and moves on. Weeks later, production doesn’t match what the schema claims it should look like.
This “schema drift” is more common than teams like to admit.
How to handle it:
Run rails db:migrate:status to spot migrations that didn’t apply cleanly. Identify what failed, fix the underlying issue, and reapply the missing steps instead of forcing things forward blindly.
3. Data Type Mismatches
Changing a column from string to integer (or any strict type) sounds simple, until existing data doesn’t comply.
One invalid value can bring the entire migration to a halt.
How to handle it:
Avoid direct type changes on live data. Instead:
- Create a new column with the desired type
- Migrate data in safe, validated batches
- Swap columns once everything checks out
This approach is slower, but far safer.
4. Long-Running or Locked Queries
Large tables don’t like being altered casually. Adding indexes, updating millions of rows, or modifying constraints can lock your database, and that’s when alerts start firing.
How to handle it:
Break migrations into smaller steps. Use batch updates for data changes. When supported, rely on database-specific features like concurrent index creation to reduce locking.
5. Foreign Key and Constraint Failures
Dropping or modifying constraints can fail if related data still exists, even if that data shouldn’t be there.
How to handle it:
Before touching constraints, clean up invalid or orphaned data. Make data integrity part of the migration plan, not an afterthought.
6. Rollback Failures
Not all Rails migrations are reversible. Dropping a column doesn’t magically bring the data back when you roll back.
How to handle it:
Always assume rollbacks are risky. Test them in staging, document irreversible steps clearly, and rely on verified backups for anything destructive.
Rollbacks are safety nets, not time machines.
7. Environment Mismatches
A migration works perfectly on your machine… then fails in production.
Different database versions, missing extensions, or adapter quirks are usually to blame.
How to handle it:
Keep staging as close to production as possible. If production runs PostgreSQL 14 with specific extensions, staging should too. “Close enough” isn’t close enough for migrations.
8. Data Loss Risks
Commands like drop_table or remove_column are fast, powerful, and unforgiving.
How to handle it:
Double-check destructive operations. Communicate them clearly. And never, ever run them without reliable backups in place.
Final Thought
Rails migrations are less about writing perfect code and more about understanding how data behaves over time, especially under load, with real users and real edge cases.
Issues don’t mean you did something wrong. They mean your application is alive, evolving, and growing.
Approach migrations with patience, caution, and a healthy respect for production data and they’ll stop feeling scary and start feeling manageable.
And if you ever feel stuck while building, migrating, or upgrading your Rails application, our team of expert developers at RailsFactory is always around to help you think through the problem and find a safe path forward.
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