# Type Inference

Locality IDB provides powerful type inference utilities out of the box. Instead of hand-crafting TS interfaces for selection, insertion, and update payloads, you can infer them directly from your schema definitions.

```typescript
import { defineSchema, column } from 'locality-idb';
import type { InferSelectType, InferInsertType, InferUpdateType } from 'locality-idb';

const schema = defineSchema({
  users: {
    id: column.int().pk().auto(),
    name: column.text(),
    email: column.text().unique(),
    age: column.int().optional(),
    createdAt: column.timestamp(),
  },
});

// 1. Infer the full row type returned from select queries
type User = InferSelectType<typeof schema.users>;
/*
Type inferred as:
{
  id: number;
  name: string;
  email: string;
  age?: number;
  createdAt: string;
}
*/

// 2. Infer the insert payload type (auto-generated columns like pk and timestamps are optional)
type InsertUser = InferInsertType<typeof schema.users>;
/*
Type inferred as:
{
  name: string;
  email: string;
  age?: number;
  id?: number;         // Optional because of .auto()
  createdAt?: string;  // Optional because it auto-generates a timestamp
}
*/

// 3. Infer the update payload type (primary keys are omitted, other fields are optional)
type UpdateUser = InferUpdateType<typeof schema.users>;
/*
Type inferred as:
{
  name?: string;
  email?: string;
  age?: number;
  createdAt?: string;
}
*/
```