fix avoid crash if book does not exists anymore

Author: marcorobol

.env.example

@@ -12,6 +12,7 @@ SUPER_SECRET='your-secret-key'
 # Url to the MongoDb database
 # DB_URL='your-db-url-with-user-and-password'
 DB_URL='mongodb://127.0.0.1:27017'
+DB_URL='mongodb+srv://<user>:<password>@cluster0.jyosd.mongodb.net/?retryWrites=true&w=majority'
 
 # Path to external frontend - If not provided, basic frontend in static/index.html is used
 FRONTEND='../EasyLibVue/dist'

app/booklendings.js

@@ -27,12 +27,12 @@ router.get('', async (req, res) => {
         return {
             self: '/api/v1/booklendings/' + dbEntry._id,
             student: {
-                self: '/api/v1/students/' + dbEntry.student._id,
-                email: dbEntry.student.email
+                self: '/api/v1/students/' + dbEntry.student?._id,
+                email: dbEntry.student?.email
             },
             book: {
-                self: '/api/v1/books/' + dbEntry.book._id,
-                title: dbEntry.book.title
+                self: '/api/v1/books/' + dbEntry.book?._id,
+                title: dbEntry.book?.title
             }
         };
     });

scripts/clearBooks.js

@@ -1,12 +1,11 @@
 require('dotenv').config()
-var Books   = require('../app/models/book'); // get our mongoose model
+var mongoose = require('mongoose');
 
+var Books = require('../app/models/book'); // get our mongoose model
 
-
-var mongoose    = require('mongoose');
 // connect to database
 mongoose.connect(process.env.DB_URL)
-.then ( async () => {
+.then( async () => {
 	console.log("Connected to Database")
 
 	// Clear books