add database cleaning at start

index.js

@@ -29,3 +29,6 @@ var mongoDB = config.get('dbConfig.host');
 mongoose.connect(mongoDB, { useNewUrlParser: true, useUnifiedTopology: true });
 var db = mongoose.connection;
 db.on('error', console.error.bind(console, 'MongoDB connection error:'));
+
+// Delete previous content of the database
+db.dropDatabase();