fix(Single Statement Deletions): Prevent Mongo timeouts caused by store recounts. (#1506 - [LL-293](https://learningpool.atlassian.net/browse/LL-293))

#1506
https://learningpool.atlassian.net/browse/LL-293

Author: PrinceWaune

api/src/routes/HttpRoutes.js

@@ -64,8 +64,8 @@ import personaIdentifierRESTHandler from 'api/routes/personas/personaIdentifierR
 import UserOrganisationsRouter from 'api/routes/userOrganisations/router';
 import UserOrganisationSettingsRouter from 'api/routes/userOrganisationSettings/router';
 import BatchDelete from 'lib/models/batchDelete';
-import getOrgFromAuthInfo from 'lib/services/auth/authInfoSelectors/getOrgFromAuthInfo';
-import { updateStatementCountsInOrg } from 'lib/services/lrs';
+import getLrsFromAuthInfo from 'lib/services/auth/authInfoSelectors/getLrsFromAuthInfo';
+import { decrementStatementCount } from 'lib/services/lrs';
 import * as routes from 'lib/constants/routes';
 
 const router = new express.Router();
@@ -361,8 +361,9 @@ restify.serve(router, Statement, {
   postDelete: (req, _, next) => {
     // Update LRS.statementCount
     const authInfo = getAuthFromRequest(req);
-    const organisationId = getOrgFromAuthInfo(authInfo);
-    updateStatementCountsInOrg(organisationId)
+    const lrsId = getLrsFromAuthInfo(authInfo);
+
+    decrementStatementCount(lrsId)
       .then(() => next())
       .catch(err => next(err));
   },

lib/models/lrs.js

@@ -58,4 +58,11 @@ schema.statics.updateStatementCount = async (lrs) => {
   });
 };
 
+schema.statics.decrementStatementCount = async (lrs) => {
+  getConnection()
+    .model('Lrs')
+    .update({ _id: lrs._id }, { $inc: { statementCount: -1 } })
+    .exec();
+};
+
 export default getConnection().model('Lrs', schema, 'lrs');

lib/services/auth/authInfoSelectors/getLrsFromAuthInfo.js

@@ -0,0 +1,5 @@
+import get from 'lodash/get';
+
+export default authInfo =>
+  get(authInfo, ['client', 'lrs_id'], {});
+

lib/services/lrs.js

@@ -6,3 +6,10 @@ export const updateStatementCountsInOrg = async (organisationId) => {
   const lrsList = await Lrs.find({ organisation: organisationId });
   await Promise.map(lrsList, Lrs.updateStatementCount);
 };
+
+export const decrementStatementCount = async (lrsId) => {
+  const lrs = await Lrs.findOne({ _id: lrsId });
+  if (lrs) {
+    await Lrs.decrementStatementCount(lrs);
+  }
+};