Mongo: Update value of string array element using the element itself

Question

I have an express app, and I am using mongodb for my DB needs. My collection structure is as follow.

Collection has documents like the one below.

{
    _id: 5caa266c58b170106ff17f40,
    title: "Test2 88 bulkWrite",
    last_save_date: 2019-04-07T17:08:25.149+00:00,
    created_by: "McufNwnQX8YXC0tNSa1fdbt9Tus2",
    stories: [ { story_id: "1", objects: [...] },
               { story_id: "2", objects: [...] },
               { story_id: "3", objects: [...] },
                ... 
             ]    
 }

The ask is simple, when let's say a user clicks a button, the array element {story_id: "2", objects: [...]} is deleted, and all the elements with story_id of more than "2" ( s.a., "3", "4"...) are decremented by one (become "2" and "3").

The first part, i.e., delete has been accomplished, but it's the second part which eludes me. Here is the code:

var storyId = ... (fetch from a request);
var intStoryId = parseInt( storyId) ;

var arrayOfHigherNumber = function() {
    var temp = [];
    if ( intStoryId == 5 ) { return temp; }
    for ( var i = intStoryId + 1; i <= 5; i++ ) {
        temp.push( i.toString() );
    }
    return temp;
}

collection.bulkWrite([
// This works and is able to delete the particular story_id entry
    { updateOne: {
        'filter': {'_id' : ObjectID( docId ) },
        'update': { 
            '$pull': { 'stories': { 'story_id': storyId } }
        }
    }},
// This does NOT work. 
    { updateMany: {
        'filter': { '_id': ObjectID( docId ), 'story_id': { '$in': arrayOfHigherNumber() } },
        'update': {
            '$set': { 'stories': { 'story_id': ( parseInt( 'story_id', 10 ) - 1 ).toString() } 
         }
     }
   }}
])

I have been banging my head against the wall for the last 24 hours and have tried many approaches, including NumberInt, $int, $convert, and several more such as aggregation pipelines, but I have not been able to accomplish this. It seems simple to be accomplished easily, but alas! Please note the story_id is a string, hence it's not that straightforward to use, let's say, a $inc operator.

EDIT

Answer by Anthony Winzlet is correct. I handled it just a bit differently, that's all.

My method

collection.findOneAndUpdate(
    { "_id": ObjectID( docId) },
    { "$pull": { "stories": { "story_id": storyId } } },
    { returnOriginal: false }
)
.then( function( story ) {
    collection.findOneAndUpdate(
        { "_id" : ObjectID( docId ) },
        { "$set": {
            "stories": story.value.stories.map(a => {
                if ( parseInt( a.story_id, 10 ) > parseInt( storyId, 10 ) ) {
                    return { story_id: (parseInt( a.story_id, 10 ) - 1).toString(), objects: a.objects }
                } else {
                    return { story_id: a.story_id , objects: a.objects }
                }
            })
        }}
    )
    .then( function ( result ) {
        response.send( result );
        client.close();
    })
})

Firstly you cannot use the aggregation operators inside the update query. And second what is the type of the story_id field? — Ashh
– Ashh, Commented Apr 9, 2019 at 18:39
It will be better if you can change it to integer value and then you can easily use arrayFilters to update the story_id. If not then you have to use iteration using find query first and then will have to update. — Ashh
– Ashh, Commented Apr 9, 2019 at 18:44
Actually I thought of that earlier as well, but as per my logic a whole JSON is being saved as a document, and I have no control for a pre-conversion in JS using NumberInt, etc. before adding the collection in the DB. However, find seems promising. — Manganese
– Manganese, Commented Apr 9, 2019 at 18:46

Ashh · Accepted Answer · 2019-04-09 20:22:49Z

1

Instead of bulk query use two operations using async await

const story = await collection.findOneAndUpdate(
  { "_id" : ObjectID( docId ) },
  { "$pull": { "stories": { "story_id": storyId } }},
  { "new": true }
)

const update = await collection.findOneAndUpdate(
  { "_id" : ObjectID( docId ) },
  { "$set": {
    "stories": story.stories.map((a, i) => { if (parseInt(a.story_id) > parseInt(story_id)) return { story_id: parseInt(a.story_id) + 1 }})
  }}
)

edited Apr 9, 2019 at 20:22

answered Apr 9, 2019 at 20:02

Ashh

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6 Comments

Manganese Over a year ago

This seems promising, what is story here in story.stories.map(...) ? Should that be a positional operator, s.a., $ ? Running it in the same form will throw Reference Error

Ashh Over a year ago

What is the error? And it should be $set operator. Updated the answer

Manganese Over a year ago

Yeah I could get it'd be $set. Error: ReferenceError: story is not defined

Ashh Over a year ago

Check my above both the query I have defined the story in the first query. So not possible

Manganese Over a year ago

Let me check it more thoroughly, because logically you are right and everything should work.

|

Aiyush Dhar · Accepted Answer · 2019-04-09 18:43:51Z

0

collection.updateMany({ story_id : { $gte : deletedElementNo } }, { $inc : { story_id: -1 } });

I think this is something of the sort you are looking for?

answered Apr 9, 2019 at 18:43

Aiyush Dhar

213 bronze badges

1 Comment

Manganese Over a year ago

story_id is a string unfortunately.

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