Question

I’m attempting to create my own todo list using Javascript, Python and MongoDB. I’m getting stuck on how to handle the task ordering.

My current idea is to have an order field in each task document and when the order changes on the client I would grab the task list from the db and reorder each task individually/sequentially. This seems awkward because large todo lists would mean large amount of queries. Is there a way to update a field in multiple documents sequentially?

I’m also looking for advice as to whether this is the best way to do this. I want to be able to maintain the todo list order but maybe I’m going about it the wrong way.

{
  "_id" : ObjectId("50a658f2cace55034c68ce95"),
  "order" : 1,
  "title" : "task1",
  "complete" : 0
}

{
  "_id" : ObjectId("50a658fecace55034c68ce96"),
  "order" : 2,
  "title" : "task2",
  "complete" : 1
}

{
  "_id" : ObjectId("50a65907cace55034c68ce97"),
  "order" : 3,
  "title" : "task3",
  "complete" : 1
}

{
  "_id" : ObjectId("50a65911cace55034c68ce98"),
  "order" : 4,
  "title" : "task4",
  "complete" : 0
}

{
  "_id" : ObjectId("50a65919cace55034c68ce99"),
  "order" : 5,
  "title" : "task5",
  "complete" : 0
}

Answer 1

Mongo is very very fast with queries, you should not be as concerned with performance as if you were using a full featured relational database. If you want to be prudent, just create a todo list of 1k items and try it out, it should be pretty instant.

for (var i = 0; i < orderedListOfIds.length; i++)
{
  db.collection.update({ '_id': orderedListOfIds[i] }, { $set: { order:i } })
}

then

db.collection.find( { } ).sort( { order: 1 } )