Add type inference from queryFn return type in query-db-collection #356
Description
Description
Currently, query-db-collection requires explicit type parameters or schema for type inference. This issue proposes adding support for inferring types from the queryFn return type, similar to how electric-db-collection uses its ResolveType system.
Current Behavior
Users must provide types in one of these ways:
// Explicit type parameter
const collection = createCollection<Todo>(queryCollectionOptions({...}))
// Schema inference
const collection = createCollection(queryCollectionOptions({
schema: todoSchema,
...
}))Proposed Enhancement
Add automatic type inference from queryFn when no explicit type or schema is provided:
// Type would be inferred from queryFn return type
const collection = createCollection(queryCollectionOptions({
queryFn: async () => {
const response = await fetch('/api/todos')
return response.json() as Todo[] // Type inferred from here
},
...
}))Implementation Details
1. Create Type Helper
type InferQueryFnOutput<TQueryFn> = TQueryFn extends (
context: QueryFunctionContext<any>
) => Promise<Array<infer TItem>>
? TItem
: never2. Add ResolveType System
type ResolveType<
TExplicit = unknown,
TSchema extends StandardSchemaV1 = never,
TQueryFn = unknown,
> =
unknown extends TExplicit
? [TSchema] extends [never]
? InferQueryFnOutput<TQueryFn> extends never
? Record<string, unknown> // fallback
: InferQueryFnOutput<TQueryFn>
: InferSchemaOutput<TSchema>
: TExplicit3. Update QueryCollectionConfig
Update the interface to use the new type resolution system, with priority:
- Explicit type (highest priority)
- Schema inference
- QueryFn return type inference
- Fallback to Record<string, unknown>
Benefits
- Better developer experience with automatic type inference
- Consistency with electric-db-collection's flexible type system
- Reduces boilerplate when types are already defined in queryFn
Testing Requirements
- Test type inference with various queryFn patterns
- Ensure backward compatibility with existing usage
- Verify priority order of type resolution
Related
- Similar to electric-db-collection's ResolveType implementation in packages/electric-db-collection/src/electric.ts:47-57