kotlin-best-practices

Kotlin Best Practices — Quick Reference

Null Safety

!! is banned. Use ?., ?:, or null check for smart cast.

See code-patterns.md for all null safety examples.

Either Error Handling

Managers return Either<ClientException, T> -- never throw. Controllers unwrap with .throwOrValue().

See code-patterns.md for manager + controller examples.

Enum Usage

Never hardcode strings when an enum exists. Use EnumName.VALUE.value everywhere.

See code-patterns.md for enum definition and usage patterns.

Exposed ORM Patterns

Extend UUIDTable, use text() not varchar(). Always filter deletedAt.isNull(). Soft delete via timestamp update, never hard delete.

See code-patterns.md for table, query, and soft delete examples.

Transaction Rules

Reads use db.replica, writes use db.primary. Multi-table writes go in one transaction block -- all succeed or all rollback.

See code-patterns.md for transaction examples.

Conversion Pattern

Put companion object { fun from(entity) } inside Response DTOs. Never create separate mapper files.

See code-patterns.md for the full pattern.

What to Avoid

• !! -- always use ?., ?:, or null check
• @Suppress -- fix the root cause
• Throwing exceptions -- return Either.left() instead
• VARCHAR in SQL -- use TEXT
• Hardcoded strings for enum values
• Table base class -- use UUIDTable
• Field injection -- use constructor injection