CODEWITHSUNDEEP
arraysmongodbnested
src091
src091

Reputation: 2847

Updating nested arrays in mongodb

I have a document in mongodb with 2 level deep nested array of objects that I need to update, something like this:

{
    id: 1,
    items: [
        {
            id: 2,
            blocks: [
                {
                    id: 3
                    txt: 'hello'
                }
            ]
        }
    ] 
}

If there was only one level deep array I could use positional operator to update objects in it but for second level the only option I've came up is to use positional operator with nested object's index, like this:

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

This approach works but it seems dangerous to me since I'm building a web service and index number should come from client which can send say 100000 as index and this will force mongodb to create an array with 100000 indexes with null value.

Are there any other ways to update such nested objects where I can refer to object's ID instead of its position or maybe ways to check if supplied index is out of bounds before using it in query?

Upvotes: 51

Views: 30222

Answers (6)

Prat
Prat

Reputation: 1

This is pymongo function for find_one_and_update. I searched a lot to find the pymongo function. Hope this will be useful

find_one_and_update(filter, update, projection=None, sort=None, return_document=ReturnDocument.BEFORE, array_filters=None, hint=None, session=None, **kwargs)

Example

db.pymongo_object.find_one_and_update( filter = {'id' : 1}, update= {$set: {"items.$[array1].blocks.$[array2].txt": "hi"}}, array_filters =[{"array1.id" :2}, {"array2.id": 3}])

Also see pymongo documentation.

Upvotes: 0

Katya Kamenieva
Katya Kamenieva

Reputation: 376

db.col.update({"items.blocks.id": 3},
{ $set: {"items.$[].blocks.$[b].txt": "bonjour"}},
{ arrayFilters: [{"b.id": 3}] }
)

https://docs.mongodb.com/manual/reference/operator/update/positional-filtered/#update-nested-arrays-in-conjunction-with

Upvotes: 1

Pier-Luc Gendreau
Pier-Luc Gendreau

Reputation: 13814

Building on Gates' answer, I came up with this solution which works with nested object arrays:

db.objects.updateOne({
  ["items.id"]: 2
}, {
  $set: {
    "items.$.blocks.$[block].txt": "hi",
  },
}, {
  arrayFilters: [{
    "block.id": 3,
  }],
});

Upvotes: 5

Cuong Le Ngoc
Cuong Le Ngoc

Reputation: 11975

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'}})

Upvotes: 1

Gates VP
Gates VP

Reputation: 45277

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} ] } )

Upvotes: 30

Seraj
Seraj

Reputation: 31

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.

Upvotes: 3

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