Core

This package contains core types and interfaces that all Gadget client implementations must conform to. @gadgetinc/core defines the contracts for API clients, connections, model managers, records, and operations that are shared across all generated Gadget clients.

Note that developers shouldn't need to use this package directly and should instead use their generated client plus framework-specific binding packages like @gadgetinc/react.

Overview

@gadgetinc/core provides the type system foundation for the Gadget framework. It exports TypeScript types and interfaces that:

- Define what a Gadget API client looks like (AnyClient)
- Specify how connections to Gadget backends work (AnyConnection)
- Describe model managers and their operations (AnyModelManager, AnyInternalModelManager)
- Define record shapes and behavior (GadgetRecord, GadgetRecordList)
- Provide filter, sort, and selection types for querying data
- Declare action and function metadata structures

Key Exports

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- AnyClient - Interface for any Gadget app's API client instance. Defines methods like query(), mutate(), transaction(), and properties like connection and internal.
- AnyConnection - Interface for managing the connection to a Gadget backend, including authentication, GraphQL client access, and transaction support.
- AnyCoreImplementation - Interface for core utility functions like GadgetRecord construction, variable disambiguation, and error handling.

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- AnyModelManager - Generic interface representing one model's API (e.g., api.widget). Provides methods like findOne(), findMany(), findFirst().
- AnyInternalModelManager - Interface for internal API model managers used within Gadget backend code.
- GadgetRecord - Represents one record returned from a Gadget API call. Includes helper methods for change tracking, field access, and serialization.
- GadgetRecordList - An array of GadgetRecord instances with built-in pagination support (hasNextPage, nextPage(), etc.).

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- ActionFunction - Metadata and types for model actions (create, update, delete, custom actions).
- BulkActionFunction - Metadata for bulk operations on multiple records.
- GlobalActionFunction - Metadata for global actions not tied to a specific model.
- ViewFunction - Metadata for backend view queries.

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The package exports comprehensive type definitions for querying Gadget data:

- Filter types: IDFilter, StringFilter, IntFilter, FloatFilter, DateTimeFilter, JSONFilter, BooleanFilter, StateFilter, etc.
- AnyFilter - Union type for all filter types, supporting AND, OR, and NOT combinators.
- AnySort - Type for sort orders, including field-based sorting and vector similarity sorting.
- FieldSelection - Type for selecting specific fields from GraphQL responses.
- Options types: FindManyOptions, BaseFindOptions, InternalFindOptions, etc.

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- Select - Type utility for extracting a subset of a schema based on a selection.
- DefaultSelection - Type utility for defaulting selections when none are provided.
- AvailableSelection - Converts a schema type into valid selection options.
- Scalar types: GadgetID, DateTime, EmailAddress, URLString, JSONBlob, CurrencyAmount, etc.

Architecture

The @gadgetinc/core package uses TypeScript's structural typing to define contracts without imposing implementation details. Generated Gadget clients implement these interfaces, ensuring consistent APIs across all apps.

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The package exports symbols used to attach internal state to client objects:

``typescript
export const $modelRelationships = Symbol.for("gadget/modelRelationships");
export const $coreImplementation = Symbol.for("gadget/coreImplementation");
`

These symbols allow generated clients to store metadata and implementation details without polluting the public API surface.

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GadgetRecord includes built-in change tracking to detect modifications:

`typescript
record.changed(); // Returns true if any field has changed
record.changes(); // Returns { field: { current, previous } } for changed fields
record.flushChanges(); // Marks current state as "saved"
record.revertChanges(); // Reverts to last saved state
`

This enables optimistic UI updates and efficient data synchronization.

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GadgetRecordList extends Array with pagination helpers:

`typescript
list.hasNextPage; // boolean
list.endCursor; // string cursor for next page
await list.nextPage(); // Fetches next page of results
`

This implements Relay-style cursor pagination across all Gadget APIs.

For Gadget Developers

This package is the single source of truth for type definitions across the Gadget ecosystem. When adding new features:

1. Define types here first in @gadgetinc/core
2. Have generated clients implement the new types
3. Update framework packages (@gadgetinc/react, etc.) to leverage the new types
4. Ensure backward compatibility or coordinate breaking changes

The testing/ subdirectory exports test utilities like mockUrqlClient for use in other packages' test suites.

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After releasing a new version of @gadgetinc/core, ensure that:

1. Generated clients are regenerated to use the new version
2. Framework packages like @gadgetinc/react and @gadgetinc/client-hooks are updated
3. The PlatformDependencyVersions` variable in Gadget mainline is updated