allow exporting async functions as databases in json2graphql (#1543)

community/tools/json2graphql/README.md

@@ -202,6 +202,21 @@ module.exports = {
 };
 ```
 
+If you need to do some asynchronous stuff before exporting your data, you can
+also export an function:
+
+*Note: You can require [node-fetch](https://www.npmjs.com/package/node-fetch) in your function*
+
+```js
+const fetch = require('node-fetch');
+
+module.exports = async function() {
+  
+  const db = await fetch (...)
+  return db
+}
+```
+
 ## Use cases
 
 ### Play with GraphQL on your MongoDB data

community/tools/json2graphql/example-datasets/function.js

@@ -0,0 +1,33 @@
+const fetch = require('node-fetch');
+
+const db = async () => {
+  const response = await fetch(
+    'https://bazookaand.herokuapp.com/v1alpha1/graphql',
+    {
+      method: 'POST',
+      headers: {
+        'x-hasura-access-key': 'advancedbitch'
+      },
+      body: JSON.stringify({
+        query: `
+          query {
+            items {
+              id
+              item
+              order_id
+            }
+            users {
+              id
+              name
+              balance
+            }
+          }
+        `,
+      })
+    }
+  );
+  const respObj = await response.json();
+  return respObj.data;
+}
+
+module.exports = db;

community/tools/json2graphql/src/command.js

@@ -23,7 +23,7 @@ class JSON2GraphQL extends Command {
     if (!db) {
       throw new CLIError('path to sample database is required: \'json2graphql <url> -d ./db.js\'');
     }
-    const dbJson = this.getDbJson(db);
+    const dbJson = await this.getDbJson(db);
     const headers = key ? {'x-hasura-access-key': key} : {};
     const urlVerification = await this.verifyUrl(safeUrl, headers);
     if (urlVerification.error) {
@@ -35,7 +35,8 @@ class JSON2GraphQL extends Command {
   }
 
   getDbJson(db) {
-    return require(resolve(db));
+    const ret = require(resolve(db));
+    return typeof ret === 'function' ? ret() : ret;
   }
 
   getSafeUrl(url) {