Canvas Data Fetching

Data fetching

Project type

Before applying this skill, check package.json for a dependency named @drupal-canvas/headless or starting with @drupal-canvas/headless-. If one is present, this is a Canvas Headless codebase — read canvas-headless first. In headless projects the drupal-canvas package (including its JsonApiClient) is not supported: fetch page trees with the SDK's fetchPage() and content with the SDK's JSON:API client (getClient()), using the framework's idiomatic data-loading path. Do not copy the SWR + JsonApiClient patterns below into a headless codebase. The content-modeling workflow in this skill (identifying content types, verifying queries, checking deserialized shapes) still applies conceptually. If no such dependency is present, this is a Canvas-rendered React codebase: components are React (index.jsx/.tsx) and everything in this skill applies as written. These are the only two project types.

Data fetching with SWR

Use SWR for all data fetching. It provides caching, revalidation, and a clean hook-based API.

import useSWR from 'swr';

const fetcher = (url) => fetch(url).then((res) => res.json());

export default function Profile() {
  const { data, error, isLoading } = useSWR(
    'https://my-site.com/api/user',
    fetcher,
  );

  if (error) return <div>Failed to load</div>;
  if (isLoading) return <div>Loading...</div>;
  return <div>Hello, {data.name}!</div>;
}

Fetching Drupal content with JSON:API

To fetch content from Drupal (e.g., articles, events, or other content types), use the autoconfigured JsonApiClient from the drupal-canvas package combined with DrupalJsonApiParams for query building.

Important: Keep the default serializer enabled in final component code. The runtime contract for Canvas components is the deserialized shape returned by JsonApiClient, not the raw JSON:API document shape.

Important: Do not fabricate JSON:API resource payloads in Workbench mocks. Components that fetch data should render their real loading, empty, or error states in Workbench unless the user explicitly asks for a static, non-fetching preview shape.

Raw JSON:API vs deserialized Canvas data

Do not write component logic from raw JSON:API assumptions such as data[0].attributes.title or data[0].relationships.field_image. Components using JsonApiClient receive deserialized objects instead.

• Use plain HTTP requests only for connectivity checks and broad endpoint existence.
• Use JsonApiClient to inspect the actual shape your component will consume.
• If you inspect the raw JSON:API document for debugging, treat it as a secondary diagnostic view, not the source of truth for component code.
• Do not disable the serializer in final component code.

Verify every JSON:API request returns the expected results

Any JSON:API request you generate — for a new component, a refactor, a filter change, an added include, a changed sort, or a new query for an existing component — must be executed and verified before any rendering logic is written or changed against it. Do not assume a query is correct because it "looks right". Build the query, run it, and confirm the response matches expectations.

A request is verified only after all of these checks pass:

• It runs. No HTTP error, no JSON:API error document, no client exception.
• The result count matches expectations. A list query should return a non-empty collection when content of that type exists. A filtered query should return fewer items than the unfiltered query (and zero only when zero is genuinely expected). A single-resource fetch should return one resource, not null.
• The expected fields are present and populated on the deserialized objects — including fields requested via addFields. Missing or consistently null fields mean the query, the field name, or the content type is wrong.
• Includes resolved to real related entities, not bare references. If you used addInclude, confirm the relationship is hydrated on the deserialized object the component will read.
• Filters and sorts behave as intended. Spot-check that filtered items actually match the filter criteria and sorted items are in the requested order.

If any check fails, fix the query, the field names, or the content-type assumptions — not the component. Do not paper over an empty or wrong response with optional chaining, fallback strings, or "looks fine in the UI" reasoning. Re-run the probe after each fix and only proceed once the response matches expectations.

Use the probe pattern in the next section as the default mechanism for these checks. A probe that prints count: 0, keys: [], or a shape missing the fields the component needs is a failed verification, not a green light.

Probe the deserialized shape before coding

Before writing rendering logic, run a one-off JavaScript probe that uses the same JsonApiClient call and DrupalJsonApiParams query pattern the component will use. Inspect the first returned item and write the component against that deserialized shape.

This probe runs outside the Canvas runtime, so it must provide baseUrl and apiPrefix explicitly. Final component code should not copy that setup; Canvas-provided component code should use the normal autoconfigured new JsonApiClient() path instead.

Use a command in this pattern:

node --input-type=module -e "
globalThis.window = {};
import { JsonApiClient } from 'drupal-canvas';
import { DrupalJsonApiParams } from 'drupal-jsonapi-params';

const describeShape = (value) => {
  if (Array.isArray(value)) {
    return value.length > 0 ? [describeShape(value[0])] : ['empty-array'];
  }
  if (value && typeof value === 'object') {
    return Object.fromEntries(
      Object.entries(value).map(([key, nestedValue]) => [key, describeShape(nestedValue)]),
    );
  }
  if (value === null) {
    return 'null';
  }
  return typeof value;
};

const client = new JsonApiClient('https://example.ddev.site', {
  apiPrefix: 'jsonapi',
});
const queryString = new DrupalJsonApiParams()
  .addSort('created', 'DESC')
  .addFields('node--article', ['title', 'created', 'body', 'path'])
  .getQueryString();

const items = await client.getCollection('node--article', { queryString });
const first = items?.[0];

console.log('count:', items?.length ?? 0);
console.log('keys:', first ? Object.keys(first) : []);
console.log('shape:', JSON.stringify(first ? describeShape(first) : null, null, 2));
console.log(JSON.stringify(first, null, 2));
"

Pass the site root as baseUrl, not the /jsonapi endpoint. Adjust the resource type, filters, includes, sorts, and fields to match the component you are building. Do not inspect one query shape and implement a different one in the component.

If this probe fails in a local HTTPS development environment, check whether Node trusts the local certificate chain before assuming the JSON:API client or query is wrong.

import { getNodePath, JsonApiClient } from 'drupal-canvas';
import { DrupalJsonApiParams } from 'drupal-jsonapi-params';
import useSWR from 'swr';

const Articles = () => {
  const client = new JsonApiClient();
  const { data, error, isLoading } = useSWR(
    [
      'node--article',
      {
        queryString: new DrupalJsonApiParams()
          .addSort('created', 'DESC')
          .getQueryString(),
      },
    ],
    ([type, options]) => client.getCollection(type, options),
  );

  if (error) return 'An error has occurred.';
  if (isLoading) return 'Loading...';
  return (
    <ul>
      {data.map((article) => (
        <li key={article.id}>
          <a href={getNodePath(article)}>{article.title}</a>
        </li>
      ))}
    </ul>
  );
};

export default Articles;

Including relationships with addInclude

When you need related entities (e.g., images, taxonomy terms), use addInclude to fetch them in a single request.

Avoid circular references in JSON:API responses. SWR uses deep equality checks to compare cached data, which fails with "too much recursion" errors when the response contains circular references.

Do not include self-referential fields. Fields that reference the same entity type being queried (e.g., field_related_articles on an article query) create circular references: Article A references Article B, which references back to Article A. If you need related content of the same type, fetch it in a separate query.

Use addFields to limit the response. Always specify only the fields you need. This improves performance and helps avoid circular reference issues:

const params = new DrupalJsonApiParams();
params.addSort('created', 'DESC');
params.addInclude(['field_category', 'field_image']);

// Limit fields for each entity type
params.addFields('node--article', [
  'title',
  'created',
  'field_category',
  'field_image',
]);
params.addFields('taxonomy_term--categories', ['name']);
params.addFields('file--file', ['uri', 'url']);

Creating content list components

When building a component that displays a list of content items (e.g., a news listing, event calendar, or resource library), follow this workflow:

Setup gate

Before any JSON:API discovery or content-type checks, verify local setup:

1. Resolve Canvas config values before writing code or probing Drupal. Check, in this order:
   • shell environment variables
   • .env in the project root
   • ~/.canvasrc
2. Determine the effective CANVAS_SITE_URL.
3. Determine the effective CANVAS_JSONAPI_PREFIX. If it is not set, default to jsonapi.
4. Record the resolved values before continuing:
   • CANVAS_SITE_URL=<resolved site root>
   • CANVAS_JSONAPI_PREFIX=<resolved prefix>
5. Verify that CANVAS_SITE_URL is the site root, not the JSON:API endpoint. For example, use https://example.ddev.site, not https://example.ddev.site/jsonapi.
6. Send an HTTP request to {CANVAS_SITE_URL}/{resolved JSON:API prefix}. Success means HTTP 200.
7. If the request is successful, continue with Drupal data fetching.
8. If the request is unsuccessful (or required values are missing), ask the user whether they want to:
   • Configure Drupal connectivity now, or
   • Continue with static content instead of Drupal fetching.
9. If the user chooses to configure connectivity, provide setup instructions:
   • CANVAS_SITE_URL=<their Drupal site root>
   • CANVAS_JSONAPI_PREFIX=jsonapi (optional; defaults to jsonapi) Then wait for the user to confirm they updated shell env, .env, or ~/.canvasrc, and resolve the values again before retrying the request.
10. If the user chooses not to configure connectivity, proceed with static content.
11. Do not start content-type discovery, field inspection, or component coding until the effective CANVAS_SITE_URL and JSON:API prefix are known.
12. Do not update Vite config (vite.config.*) to troubleshoot connectivity. Connectivity issues must be resolved via correct config values and Drupal site availability, not build tooling changes.

Step 1: Analyze the list structure

Examine the design to understand what data each list item needs:

• What fields are displayed (title, date, image, category, etc.)?
• How are items sorted (newest first, alphabetical, etc.)?
• Are there filters or pagination?

Step 2: Identify or request the content type

Before writing code, verify that an appropriate content type exists in Drupal:

1. Check the JSON:API endpoint of your local Drupal site (configured via the resolved CANVAS_SITE_URL and JSON:API prefix from the Setup gate) to find a content type that matches the required structure. A plain HTTP request is acceptable for endpoint discovery only, after passing the Setup gate.

2. If a matching content type exists, use it and note which fields are available.

3. Inspect a sample response through JsonApiClient using the same resource type and query pattern the component will use. Run a one-off probe command, inspect the first returned item, and verify the deserialized field shape before writing rendering logic.

4. If no matching content type exists, stop and prompt the user to create one. Provide:

   • A suggested content type name
   • The required field structure based on the list design

Step 3: Build the component

Create the content list component using JSON:API to fetch content. Only use fields that actually exist on the content type and on the deserialized objects returned by JsonApiClient—do not assume raw JSON:API field nesting will match the runtime data shape.

Handling filters

If the list includes filters based on entity reference fields (e.g., filter by category, filter by author):

• Do not hardcode filter options. Filter options should be fetched dynamically using JSON:API.
• Fetch the available options for each filter (e.g., all taxonomy terms in a vocabulary) and populate the filter UI from that data.

This ensures filters stay in sync with the actual content in Drupal and new options appear automatically without code changes.

Navigation / Menu Components

Components like headers, footers, and sidebars often need menu links from Drupal. Use a dual implementation: fetch from a Drupal menu when one exists, and fall back to a static array when no menu is configured yet.

This means the component works immediately (using the hardcoded fallback), and automatically upgrades to live Drupal-managed links once the CMS editor creates the corresponding menu.

import { JsonApiClient, sortMenu } from 'drupal-canvas';
import useSWR from 'swr';

// Static fallback — always define this; it renders when no Drupal menu exists
const FALLBACK_LINKS = [
  { id: 'home', title: 'Home', url: '/' },
  { id: 'about', title: 'About', url: '/about' },
];

const client = new JsonApiClient();

const Navigation = ({ menuName = 'main' }) => {
  const { data, error, isLoading } = useSWR(
    menuName ? ['menu_items', menuName] : null,
    ([type, id]) => client.getResource(type, id),
  );

  // Use live Drupal menu links when available; otherwise use fallback
  const links =
    !error && !isLoading && data ? Array.from(sortMenu(data)) : FALLBACK_LINKS;

  return (
    <nav>
      {links.map(({ id, title, url }) => (
        <a key={id} href={url}>
          {title}
        </a>
      ))}
    </nav>
  );
};

Rules for menu components:

• Always define a FALLBACK_LINKS constant with representative links. This makes the component useful in Workbench and on sites where the Drupal menu hasn't been created yet.
• Expose menuName as a prop and register it in component.yml so CMS editors can configure which Drupal menu to use without code changes.
• menuName = null disables fetching (SWR key is null) and renders the fallback — useful for pure static previews.
• After building a nav-type component, include a note in the manual steps summary telling the user to create the corresponding menu in Drupal at /admin/structure/menu/add.

component.yml example for menuName:

props:
  properties:
    menuName:
      title: Menu name
      type: string
      examples:
        - main
        - footer