add schema gneerator for activity.js

scripts/database/entry/activity.JS

@@ -9,6 +9,28 @@ class Activity extends Entry {
     constructor(PROPERTIES) {
         super(PROPERTIES);
     };
+
+    /* 
+    Generate a schema for MongoDB. 
+
+    @return {OBJECT} the schema
+    */
+    static generateTemplate() {
+        let SCHEMA = {
+            "username": {"type": String, "required": true},
+            "description": {"type": String},
+            "date": {"type": Number},
+            "duration": {"type": Number}
+        }
+        let TEST = new Activity();
+
+        // Verify that the schema is valid.
+        Object.keys(SCHEMA).forEach((KEY) => {
+            if (!Object.keys(TEST).includes(KEY)) {delete SCHEMA[KEY];};
+        });
+
+        return (SCHEMA)
+    }
 }
 
 module.exports = Activity;