Fix Gatsby CMS Preview

NOTES.md

@@ -0,0 +1,64 @@
+# Parallel Query Running
+
+With [PQR](#https://www.gatsbyjs.com/docs/reference/release-notes/v3.10/#experimental-parallel-query-running), multiple processes run queries.
+
+How to test this scenario locally: just run `gatsby build`.
+
+In this scenario, we want to only fetch data once in the main process, cache the responses and reuse them inside the workers.
+
+- `process.env.NODE_ENV` is set to `production`;
+- A first process calls `createSchemaCustomization`;
+- A number of subsequent processes (with `GATSBY_WORKER_ID` env variable set to a number) call `sourceNodes`.
+
+# Deferred Static Generation
+
+With [DSG](https://www.gatsbyjs.com/docs/reference/rendering-options/deferred-static-generation/), instead of generating every page up front, you can decide to generate certain pages at build time and others only when a user accesses the page for the first time. Subsequent page requests use the same HTML and JSON generated during the very first request to this page.
+
+How to test this scenario locally: run `gatsby build` and `gatsby serve` from the command line, and make sure some pages are marked with `defer: true`.
+
+In this scenario:
+
+- page that has not been generated yet gets requested;
+- `gatsby serve` will only call `createSchemaCustomization` (not `sourceNodes`);
+
+# Develop preview mode
+
+How to test this scenario locally: just run `gatsby develop`.
+
+In this scenario:
+
+- `process.env.NODE_ENV` is set to `development`;
+- `createSchemaCustomization` gets called;
+- `sourceNodes` gets called;
+
+# Gatsby CMS Preview
+
+This is the "CMS Preview" functionality offered by Gatsby Cloud.
+
+How to test this scenario locally?
+
+Run:
+
+```
+ENABLE_GATSBY_REFRESH_ENDPOINT=true GATSBY_EXPERIMENTAL_DISABLE_SCHEMA_REBUILD=true gatsby develop
+```
+
+The `GATSBY_EXPERIMENTAL_DISABLE_SCHEMA_REBUILD` above is important — and Gatsby Preview sets this env variable for us — because otherwise the `createSchemaCustomization` hook would be called, reloading everything from scratch.
+
+Webhooks must trigger create/update/delete/publish events on items/assets to the `/__refresh` endpoint. The webhook must have the following custom body:
+
+```
+{
+  "event_type":"{{event_type}}",
+  "entity_id":"{{#entity}}{{id}}{{/entity}}",
+  "entity_type":"{{entity_type}}"
+}
+```
+
+Also make sure to set `disableLiveReload: true` in plugin config to avoid nodes from being refreshed by Pusher notifications.
+
+In this scenario:
+
+- `process.env.NODE_ENV` is set to `development`;
+- `createSchemaCustomization` gets called;
+- `sourceNodes` gets called with the `context.webhookBody` set to the body of the incoming webhook;

package.json

@@ -1,6 +1,6 @@
 {
   "name": "gatsby-source-datocms",
-  "version": "3.0.19-0",
+  "version": "3.0.19-3",
   "description": "Gatsby source plugin for building websites using DatoCMS as data source",
   "main": "index.js",
   "repository": {

src/hooks/createSchemaCustomization/index.js

@@ -66,20 +66,20 @@ module.exports = async (
     },
   };
 
-  let activity;
+  if (!process.env.GATSBY_WORKER_ID) {
+    let activity;
 
-  activity = reporter.activityTimer(`loading DatoCMS schema`, {
-    parentSpan,
-  });
+    activity = reporter.activityTimer(`loading DatoCMS schema`, {
+      parentSpan,
+    });
 
-  activity.start();
+    activity.start();
 
-  if (!process.env.GATSBY_WORKER_ID) {
     await loader.load();
     await loader.saveStateToCache(cache);
-  }
 
-  activity.end();
+    activity.end();
+  }
 
   createTypes(context);
 };

src/hooks/sourceNodes/index.js

@@ -72,7 +72,19 @@ module.exports = async (
       `DatoCms${instancePrefix ? pascalize(instancePrefix) : ''}${type}`,
   };
 
-  if (webhookBody && Object.keys(webhookBody).length) {
+  // we need this both for Gatsby CMS Preview and live reload on local development
+
+  loader.entitiesRepo.addUpsertListener(entity => {
+    createNodeFromEntity(entity, context);
+  });
+
+  loader.entitiesRepo.addDestroyListener(entity => {
+    destroyEntityNode(entity, context);
+  });
+
+  const isWebhook = webhookBody && Object.keys(webhookBody).length > 0;
+
+  if (isWebhook) {
     const {
       entity_id: entityId,
       entity_type: entityType,
@@ -139,16 +151,8 @@ module.exports = async (
     });
   });
 
-  const queue = new Queue(1, Infinity);
-
   if (process.env.NODE_ENV !== `production` && !disableLiveReload) {
-    loader.entitiesRepo.addUpsertListener(entity => {
-      createNodeFromEntity(entity, context);
-    });
-
-    loader.entitiesRepo.addDestroyListener(entity => {
-      destroyEntityNode(entity, context);
-    });
+    const queue = new Queue(1, Infinity);
 
     loader.watch(loadPromise => {
       queue.add(async () => {