Validation Helpers on Your Models
Add reusable validation directly in shared code.
Validation Helpers on Your Models is a free Kotlin Multiplatform Academy lesson on CoddyKit — lesson 4 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Kotlin Multiplatform Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Models Can Check Themselves
A model should know what valid looks like. Adding validation to shared code means both apps enforce the same rules.
A Computed Property
A computed property derives a value from the model's fields. It runs whenever you read it, with no stored state.
data class User(val name: String) {
val isNamed: Boolean get() = name.isNotBlank()
}Expose an isValid Flag
Give the model an isValid property that bundles all its rules into one boolean both apps can trust.
val isValid: Boolean
get() = name.length in 2..30Add a Validation Method
A function on the model can run a check and return a result, keeping the logic right next to the data.
fun hasValidEmail(): Boolean =
email.contains("@")Return Specific Errors
Instead of a plain boolean, return a list of messages so the UI can tell the user exactly what to fix.
fun errors(): List<String> =
if (name.isBlank()) listOf("Name required") else emptyList()Reuse Across Fields
Extract a small helper so several models can share the same rule, like a reusable email or length check.
fun String.isEmail(): Boolean = contains("@") && contains(".")Validate in commonMain
Keep every rule in commonMain so Android and iOS validate identically and your forms never disagree.
Guard at Creation with init
An init block with require can reject bad data the moment a model is built, stopping invalid objects early.
init { require(name.isNotBlank()) { "Name required" } }Keep Validation Pure
Validation should only read fields and return results, never touch UI or network. Pure rules stay portable and testable.
Easy to Unit Test
Because the logic is plain Kotlin, you can test it once in commonTest and trust it on every platform.
Why This Matters
Shared validation means a rule changes in exactly one place and instantly applies to both apps. 🙂
Quick Check
Where should reusable model validation live?
Recap
Add validation as computed properties, methods or init checks in commonMain, keep it pure, and both apps enforce identical rules.
Frequently asked questions
Is the “Validation Helpers on Your Models” lesson free?
Yes — the full text of “Validation Helpers on Your Models” is free to read here on the web, and the Kotlin Multiplatform Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Kotlin Multiplatform Academy course, upgrade to CoddyKit PRO.
What will I learn in “Validation Helpers on Your Models”?
Add reusable validation directly in shared code. You practise Kotlin Multiplatform Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Kotlin Multiplatform Academy?
No prior experience is required. Kotlin Multiplatform Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 4 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Validation Helpers on Your Models” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Kotlin Multiplatform Academy lesson?
Yes. Every Kotlin Multiplatform Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Data Classes for Your Domain
- Enums & Sealed Classes for State
- Null Safety in Shared Models
- Validation Helpers on Your Models