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