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Clarify Fern Definition type validation section (API Definitions) #618

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Merged
merged 4 commits into from
Aug 27, 2025
Merged

Clarify Fern Definition type validation section (API Definitions) #618

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41b5a98
clarify type validation section
devalog Aug 27, 2025
c273d42
update wording
devalog Aug 27, 2025
a71136a
clarify wording even more
devalog Aug 27, 2025
a5e8fff
nit
devalog Aug 27, 2025
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26 changes: 1 addition & 25 deletions fern/products/api-def/ferndef-pages/types.mdx
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Expand Up @@ -282,7 +282,7 @@ interface Person {

### Validating types

You can add validation constraints to your types (both aliases and references) to ensure data integrity. Validation constracts are automatically enforced in generated SDKs.
You can add validation constraints to your types (both aliases and references) to ensure data integrity. These validation constraints exist in your API definition and are enforced by the server, but the generated client SDKs don't include validation logic.

<CodeBlock title="Fern Definition">
```yaml {8-11, 15-17}
Expand All @@ -305,30 +305,6 @@ types:
max: 150
```
</CodeBlock>
<CodeBlock title="Generated TypeScript SDK from Fern Definition">

```typescript
interface Person {
/** The person's full name */
name: string;
/** Age in years */
age: number;
}

// Validation is automatically enforced when creating Person objects
const client = new YourApiClient();
try {
const person = await client.createPerson({
name: "A", // Fails minLength validation
age: -5, // Fails min validation
});
} catch (error) {
if (error instanceof ValidationError) {
console.log(`Validation failed: ${error.message}`);
}
}
```
</CodeBlock>

<AccordionGroup>
<Accordion title="String validation reference">
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