MongoDB remove element out array with index

Question

I have an array in a mongodb collection and want to remove one element from it with the index, didnt found how to make it, or an operator for it...

document example:

    {
    "_id": "<someID>",
    "array": [
      {
        "elemt": 1
      },
      {
        "elemt": 2,
      },
      {
        "elemt": 2,
      }]
    }

(duplicates can occur - and dont want to delete these duplicates)

and i want to achive that an element can be removed with the index of it...

Using:

NodeJS 8.9
Mongodb 3.4
(npm) mongodb (native)
Visual Studio 17

It's not very clear... Do you want to remove duplicate element from your array? Or do you want to remove the element at a specific index of the array ? — felix, Jan 15 '18 at 11:50
i want to remove an element with the index of it, and not to remove duplicates, with that i meant: duplicates can occur - and dont want to delete these duplicates — hasezoey, Jan 15 '18 at 11:58
didnt found this before, thanks, but now: how to insert the index? i cant use the templated strings? — hasezoey, Jan 15 '18 at 12:07

Tomasz Bubała · Accepted Answer · 2018-01-15T12:50:15.753

5

I have a 2-step solution to achieve what you described.

Set your array's element to null
Find null element and $pull it from your array.
```
db.collection.update({}, {$unset : {"array.2" : 1 }});
db.collection.update({}, {$pull : {"array" : null }});
```
You can specify the _id in the query. You can't use string templates to specify the index in your query. It will throw out an error "Unexpected template string". You can use computed property:
```
var arrIndex = `array.${index}`;
/* ... */
db.collection.update({}, {$unset : {[arrIndex] : 1 }});
```

or just wrap your string literal in brackets [], like this: [array.${index}].

edited Jan 15 '18 at 12:50

answered Jan 15 '18 at 12:10

Tomasz Bubała

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thanks, but now: how to insert the index? i cant use the templated strings? – hasezoey Jan 15 '18 at 12:11
How are you trying to achieve this? What's the problem? – Tomasz Bubała Jan 15 '18 at 12:14
https://gist.github.com/hasezoey/662822b900baeb01a880b03bef223704 here it says "Unexpected template string" – hasezoey Jan 15 '18 at 12:19
can you set it into variable earlier in the code and then use it? – Tomasz Bubała Jan 15 '18 at 12:31
I updated the answer based on the data you provided. – Tomasz Bubała Jan 15 '18 at 12:42
thanks! putting it in `[]` worked, didnt knowed that... ^^ – hasezoey Jan 15 '18 at 12:58

MongoDB remove element out array with index

1 Answers1