Updating nested arrays in mongodb

Solution 1:

Here's the big question, do you need to leverage Mongo's "addToSet" and "push" operations? If you really plan to modify just individual items in the array, then you should probably build these arrays as objects.

Here's how I would structure this:

{
    id: 1,
    items: 
        { 
          "2" : { "blocks" : { "3" : { txt : 'hello' } } },
          "5" : { "blocks" : { "1" : { txt : 'foo'}, "2" : { txt : 'bar'} } }
        }
}

This basically transforms everything in to JSON objects instead of arrays. You lose the ability to use $push and $addToSet but I think this makes everything easier. For example, your query would look like this:

db.objects.update({'items.2': {$exists:true} }, {'$set': {'items.2.blocks.0.txt': 'hi'}})

You'll also notice that I've dumped the "IDs". When you're nesting things like this you can generally replace "ID" with simply using that number as an index. The "ID" concept is now implied.

This feature has been added in 3.6 with expressive updates.

db.objects.update( {id: 1 }, { $set: { 'items.$[itm].blocks.$[blk].txt': "hi", } }, { multi: false, arrayFilters: [ { 'itm.id': 2 }, { 'blk.id': 3} ] } )

Solution 2:

The ids which you are using are linear number and it has to come from somewhere like an additional field such 'max_idx' or something similar. This means one lookup for the id and then update. UUID/ObjectId can be used for ids which will ensure that you can use Distributed CRUD as well.

Solution 3:

MongoDB 3.6 added all positional operator $[] so if you know the id of block that need update, you can do something like:

db.objects.update({'items.blocks.id': id_here}, {'$set': {'items.$[].blocks.$.txt': 'hi'}})