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Choosing :sql over :ruby for schema_format in Rails

Alessio Bussolari
2 min readDec 19, 2023

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In Ruby on Rails, the configuration option config.active_record.schema_format determines the format for dumping the database schema. It can be set to either :ruby (using Ruby DSL) or :sql (using plain SQL). While :ruby is the default and works well for many applications, there are compelling reasons to consider :sql, particularly in more complex setups.

Understanding the Differences

:ruby Format:

  • Uses Ruby DSL to generate schema.rb.
  • Is database-agnostic, making it suitable for simpler applications or when switching between different DBMS (Database Management Systems).

:sql Format:

  • Generates structure.sql using raw SQL statements.
  • Captures all database-specific elements like triggers, views, stored procedures, and complex indexes.

Advantages of :sql Format

  1. Database Specific Features:
    If your application uses database-specific features like foreign key constraints, advanced indexing, triggers, or stored procedures, :sql ensures these are accurately captured in the schema file. The Ruby DSL used in schema.rb can’t always express these complex database features.
  2. Complex Indexes:
    Some complex indexing options available in databases like PostgreSQL or MySQL may not be expressible or portable in the Ruby DSL.
  3. Consistency and Reliability:
    :sql provides a more accurate representation of the database schema, ensuring consistency between different environments and reducing the risk of migration-related issues.
  4. Migration History:
    The structure.sql file can offer a more comprehensive historical view of schema changes, especially when using database-specific features.

Considerations for Using :sql Format

  • Portability: If you plan to switch between different types of databases (e.g., from MySQL to PostgreSQL), :sql format may be less portable, as it includes database-specific syntax.
  • Readability: structure.sql can be harder to read and interpret compared to the more straightforward Ruby DSL in schema.rb.

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Alessio Bussolari

Ruby on Rails programmer since 2009. Current CTO at COSMIC SRL, where I lead the team in creating innovative solutions.