Data Client Schema

1. Defining Schemas

Define schemas to represent the JSON returned by an endpoint. Compose these to represent the data expected.

Object

• Entity - represents a single unique object (denormalized)
• new Union(Entity) - polymorphic objects (A | B)
• {[key:string]: Schema} - immutable objects
• new Invalidate(Entity|Union) - to delete an Entity

List

• new Collection([Schema]) - mutable/growable lists
• [Schema] - immutable lists
• new All(Entity|Union) - list all Entities of a kind

Map

• new Collection(Values(Schema)) - mutable/growable maps
• new Values(Schema) - immutable maps

Derived / selector pattern

• new Query(Queryable) - memoized programmatic selectors

  const queryRemainingTodos = new Query(
    TodoResource.getList.schema,
    entries => entries.filter(todo => !todo.completed).length,
  );
  

  const groupTodoByUser = new Query(
    TodoResource.getList.schema,
    todos => Object.groupBy(todos, todo => todo.userId),
  );
  

2. Entity best practices

• Every Entity subclass defines defaults for all non-optional serialised fields.
• Override pk() only when the primary key ≠ id.
• pk() return type is number | string | undefined
• Override Entity.process(value, parent, key, args) to insert fields based on args/url
• static schema (optional) for nested schemas or deserialization functions
  • When designing APIs, prefer nesting entities

3. Entity lifecycle methods

• Normalize order: process() → validate() → pk() → if existing: mergeWithStore() which calls shouldUpdate() and maybe shouldReorder() + merge(); metadata via mergeMetaWithStore().
• Denormalize order: createIfValid() → validate() → fromJS().

4. Union Types (Polymorphic Schemas)

To define polymorphic resources (e.g., events), use Union and a discriminator field.

import { Union } from '@data-client/rest'; // also available from @data-client/endpoint

export abstract class Event extends Entity {
  type: EventType = 'Issue';    // discriminator field is shared
  /* ... */
}
export class PullRequestEvent extends Event { /* ... */ }
export class IssuesEvent extends Event { /* ... */ }

export const EventResource = resource({
  path: '/users/:login/events/public/:id',
  schema: new Union(
    {
      PullRequestEvent,
      IssuesEvent,
      // ...other event types...
    },
    'type', // discriminator field
  ),
});

5. Supplementary Endpoints (enrich existing entities)

When an endpoint returns partial or differently-shaped data for an entity already in cache (e.g., a metadata endpoint, a stats endpoint, a lazy-load expansion endpoint), use the same Entity as the schema — don't create a wrapper entity.

See partial-entities for patterns and examples.

6. Best Practices & Notes

• Always set up schema on every resource/entity/collection for normalization
• Normalize deeply nested or relational data by defining proper schemas
• Use Entity.schema for client-side joins
• Use Denormalize<> type from rest/endpoint/graphql instead of InstanceType<>. This will handle all schemas like Unions, not just Entity.

7. Common Mistakes to Avoid

• Don't forget to use fromJS() or assign default properties for class fields
• Manually merging or 'enriching' data; instead use Entity.schema for client-side joins

References

For detailed API documentation, see the references directory:

• Entity - Normalized data class
• Collection - Mutable/growable lists
• Union - Polymorphic schemas
• Query - Programmatic selectors
• Invalidate - Delete entities
• Values - Map schemas
• All - List all entities of a kind
• Array - Immutable list schema
• Object - Object schema
• schema - Schema overview
• relational-data - Relational data guide
• computed-properties - Computed properties guide
• partial-entities - Partial entities guide
• side-effects - Side effects guide
• sorting-client-side - Client-side sorting guide

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