When a database structure changes for an API, what specific process helps manage these changes over time in a controlled and repeatable way?

When a database structure changes for an API, the specific process that helps manage these changes over time in a controlled and repeatable way is called Database Migration, also known as Schema Migration. This process involves defining and applying incremental, version-controlled changes to a database's schema, which is its fundamental structure including tables, columns, relationships, and constraints.

The core of database migration relies on a series of migration scripts (often written in SQL or generated by Object-Relational Mappers). Each script represents a single, atomic change to the database schema, such as adding a new table, altering a column, or creating an index. These scripts are meticulously versioned, meaning they are given a unique identifier and ordered sequentially, typically stored alongside the application's code in a version control system like Git.

A dedicated migration tool or framework is then used to manage these scripts. When a database needs to be updated, this tool examines the available migration scripts and compares them against a record (usually stored in a special table within the database itself) of which migrations have already been applied to that specific database instance. It then executes only the new, unapplied scripts in their correct sequential order. This ensures that changes are applied consistently and predictably every time, regardless of the database's current state, making the process repeatable.

This systematic approach provides a controlled way to evolve the database schema because every change is explicitly defined, tracked, and applied in a specific order. It prevents manual errors, ensures that all development, testing, and production environments have the exact same schema structure at any given version, and supports rolling back changes if necessary (though the primary focus is on forward-only, additive migrations). By integrating database migrations into the development workflow, teams can automate database schema updates as part of their continuous integration and deployment pipelines, maintaining compatibility between the API and its underlying data storage as both evolve.