add script that helps a database admin find and remove tasks with duplicated IDs for a single user

migrations/duplicatedTasksFindAndRemove.js

@@ -0,0 +1,89 @@
+/*
+ * IMPORTANT:
+ *
+ * DO NOT TRUST THIS SCRIPT YET
+ *
+ *
+ * This has been written by Alys to identify and remove duplicated tasks 
+ * i.e., tasks that have the same `id` value as another task.
+ * However it could almost certainly be improved (the aggregation step HAS
+ * to be easier that this!) and Alys is still working on it. Improvements
+ * welcome.
+ *
+ * If you use it, do ALL of the following things:
+ * 
+ * - configuration, as described below
+ * - make a full backup of the user's data
+ * - be aware of how to restore the user's data from that backup
+ * - test the script first on a local copy of the database
+ * - dump the user's data to a text file before running the script so that
+ *   it can later be compared to a dump made afterwards
+ * - run the script once first with both of the db.users.update() commands
+ *   commented-out and check that the printed task IDs are correct
+ * - run the script with all code enabled
+ * - dump the user's data to a text file after running the script 
+ * - diff the two dumps to ensure that only the correct tasks were removed
+ * 
+ * 
+ * When two tasks exist with the same ID, only one of those tasks will be
+ * removed (whichever copy the script finds first).
+ * If three tasks exist with the same ID, you'll probably need to run this
+ * script twice.
+ * 
+ */
+
+
+// CONFIGURATION:
+// - Change the uuid below to be the user's uuid.
+// - Change ALL instances of "todos" to "habits"/"dailys"/"rewards" as
+//   needed. Do not miss any of them!
+
+
+var uuid='30fb2640-7121-4968-ace5-f385e60ea6c5';
+
+db.users.aggregate([
+    {$match: {'_id': uuid} },
+    {$project: { 
+        '_id':0, 'todos':1
+    }},
+    {$unwind: '$todos'},
+	{$group: {
+		_id: { taskid: '$todos.id' },
+		count: { $sum: 1 } 
+	}},
+	{ $match: { 
+		count: { $gt: 1 } 
+	}},
+	{ $project: {
+		'_id.taskid':1,
+	}},
+	{$group: {
+		_id: { taskid: '$todos.id' },
+		troublesomeIds: { $addToSet: "$_id.taskid" },
+	}},
+	{ $project: {
+		'_id':0,
+		troublesomeIds:1,
+	}},
+]).forEach(
+	function(data) {
+		// print( "\n" ); printjson(data);
+		data.troublesomeIds.forEach( function(taskid) {
+			print('non-unique task: ' + taskid);
+			db.users.update({
+					'_id': uuid,
+					'todos': { $elemMatch: { id: taskid } }
+				},
+				{ $set: { "todos.$.id" : 'de666' }
+			});
+		});
+	}
+);
+
+db.users.update(
+	{'_id': uuid},
+	{ $pull: { todos: { id: 'de666' } } },
+	{ multi: false }
+);
+
+