What are migrations?

Summary

In this chapter, we explore database migrations in Sails and why they matter.

Understanding migrations
- As your application evolves, database schemas change to accommodate new requirements.
- Changes like adding columns or indexes require migration to reflect updates in relational databases like MySQL and PostgreSQL.
- MongoDB handles schema changes more flexibly but still requires migrations for constraints like unique attributes or indexing.
Why migrations matter
- They ensure your database structure remains in sync with your Waterline models.
- They help manage breaking changes efficiently across different datastores.
Sails' approach to migrations
- Sails provides two modes for handling migrations, which will be covered in the next lessons.
- Understanding when and how to use these modes is crucial for maintaining a stable database structure.

Transcript

All right. So in this chapter, we're going to be talking about database migration and how we handle that in Sails.

We're going to kick off by looking at:

What migrations are
Why they're important
Why you should care

Why migrations matter

Let's say you're building your application, and your database is in its earliest state. You're still figuring out the client's requirements, which keep evolving. You don't know for sure what the final database structure will look like.

Over time, you’ll iterate over your database schema, making breaking changes, such as:

Adding new columns
Creating new indexes

For MongoDB, this isn’t much of a problem because new attributes can just appear in documents. But for relational databases like MySQL or PostgreSQL, if you add a new column, you need to migrate that change to the physical database.

What is migration?

Migration ensures that your Waterline model changes are reflected in your physical database (PostgreSQL, MySQL, or even MongoDB when adding constraints like unique attributes or indexes).

How Sails handles migrations

Sails provides two modes for handling database migrations.

The next two lessons will dive into these modes, explaining how they work and when to use them.