From 2b2e1d4b9aa2ef18bc091cf54716e9b9b88f557e Mon Sep 17 00:00:00 2001
From: Matteo Pagliazzi <matteopagliazzi@gmail.com>
Date: Fri, 9 Nov 2018 12:58:39 +0100
Subject: [PATCH] rewrite mongoose migration to avoid using recursion

---
 .../users/20181023_veteran_pet_ladder.js      | 88 ++++++-------------
 1 file changed, 28 insertions(+), 60 deletions(-)

diff --git a/migrations/users/20181023_veteran_pet_ladder.js b/migrations/users/20181023_veteran_pet_ladder.js
index cbe8044d53..265808d5aa 100644
--- a/migrations/users/20181023_veteran_pet_ladder.js
+++ b/migrations/users/20181023_veteran_pet_ladder.js
@@ -2,52 +2,10 @@
 const MIGRATION_NAME = '20181023_veteran_pet_ladder';
 import { model as User } from '../../website/server/models/user';
 
-function processUsers (lastId) {
-  let query = {
-    migration: {$ne: MIGRATION_NAME},
-    'flags.verifiedUsername': true,
-  };
-
-  const fields = {
-    'items.pets': 1,
-  };
-
-  if (lastId) {
-    query._id = {
-      $gt: lastId,
-    };
-  }
-
-  return User.find(query)
-    .limit(250)
-    .sort({_id: 1})
-    .select(fields)
-    .exec()
-    .then(updateUsers)
-    .catch((err) => {
-      console.log(err);
-      return exiting(1, `ERROR! ${err}`);
-    });
-}
-
 const progressCount = 1000;
 let count = 0;
 
-function updateUsers (users) {
-  if (!users || users.length === 0) {
-    console.warn('All appropriate users found and modified.');
-    displayData();
-    return;
-  }
-
-  let userPromises = users.map(updateUser);
-  let lastUser = users[users.length - 1];
-
-  return Promise.all(userPromises)
-    .then(() => {
-      return processUsers(lastUser._id);
-    });
-}
+const batchSize = 250;
 
 function updateUser (user) {
   count++;
@@ -71,24 +29,34 @@ function updateUser (user) {
   return user.save();
 }
 
-function displayData () {
-  console.warn(`\n${count} users processed\n`);
-  return exiting(0);
-}
+module.exports = async function processUsers () {
+  let query = {
+    migration: {$ne: MIGRATION_NAME},
+    'flags.verifiedUsername': true,
+  };
 
-function exiting (code, msg) {
-  code = code || 0; // 0 = success
-  if (code && !msg) {
-    msg = 'ERROR!';
-  }
-  if (msg) {
-    if (code) {
-      console.error(msg);
+  const fields = {
+    items: 1,
+  };
+
+  while (true) { // eslint-disable-line no-constant-condition
+    const users = await User // eslint-disable-line no-await-in-loop
+      .find(query)
+      .limit(batchSize)
+      .sort({_id: 1})
+      .select(fields)
+      .exec();
+
+    if (users.length === 0) {
+      console.warn('All appropriate users found and modified.');
+      console.warn(`\n${count} users processed\n`);
+      break;
     } else {
-      console.log(msg);
+      query._id = {
+        $gt: users[users.length - 1],
+      };
     }
-  }
-  process.exit(code);
-}
 
-module.exports = processUsers;
+    await Promise.all(users.map(updateUser)); // eslint-disable-line no-await-in-loop
+  }
+};