Mongo - How to update an array without creating 'duplicate'?

Question

I'm trying to do something with Mongo but I'm stuck. I'm certain the answer is super easy but I can't find it out. Thank you very much for your help.

I have a document (see below) I want to update.

{
  _id: ObjectId("57d52d9c56f0dc1c93254265"),
  processus: [
    {
      action: "action 1",
      date: ISODate("2016-08-23T22:00:00Z")
    },
    {
      action: "action 2",
      date: ISODate("2016-12-11T23:00:00Z")
    }
  ]
}

More precisely, I want to "change the date" of action 1. For example, I want to make my document like this:

{
  _id: ObjectId("57d52d9c56f0dc1c93254265"),
  processus: [
    {
      action: "action 1",
      date: "another date"
    },
    {
      action: "action 2",
      date: ISODate("2016-12-11T23:00:00Z")
    }
  ]
}

Below my update statement (which doesn't work / same thing with $push)

db.collection('...').update(
     { _id : ObjectId(...) },
     { $addToSet: {
          processus: {
            $each: [ { "action" : "action 1", "date" : "another date" } ],
          }
     }}
)

Indeed, the resulting document is:

{
  _id: ObjectId("57d52d9c56f0dc1c93254265"),
  processus: [
    {
      action: "action 1",
      date: "another date"
    },
    {
      action: "action 1",
      date: ISODate("2016-08-23T22:00:00Z")
    },
    {
      action: "action 2",
      date: ISODate("2016-12-11T23:00:00Z")
    }
  ]
}

Any idea? Thanks again.

RootHacker · Accepted Answer · 2016-09-11 17:35:58Z

1

For doing this you need to use $set with the positional operator $

db.collection('...').update(
 { _id : ObjectId("..."),
  "processus.action": "action 1" 
 },
 { $set: { 
    "processus.$.date": "another date"
 }          
})

The positional $ operator identifies an element in an array to update without explicitly specifying the position of the element in the array.The positional operator acts as a placeholder for the first entry in the array that match the filter(query document) sent to the update command.

edited Sep 11, 2016 at 17:35

answered Sep 11, 2016 at 17:19

RootHacker

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2 Comments

charnould Over a year ago

It works - almost - perfectly. Indeed, it works only if processus.action : action 1 exists. Both the id and action 1 are in the "filter part"... So how to make processus.action : action 1 be updated with another date' if it already exists, or be "insert" if it doesn't. A little bit like upsert : true` ? Thanks again.

RootHacker Over a year ago

The positional operator cannot be combined with an upsert since it requires a matching array element.

Antony Zh · Accepted Answer · 2016-09-11 11:03:18Z

0

You can use $set for an array of subdocuments with a numerical array key:

db.collection.update({ _id: ... }, { $set: { processus.0.date: another_date }})

answered Sep 11, 2016 at 11:03

Antony Zh

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2 Comments

charnould Over a year ago

Thanks. The problem is that I sort all these actions by date. So action[0] changes over time. So your proposal does not apply... Do you have any other idea? Thank you very much

Antony Zh Over a year ago

In this case you have to rewrire a whole array, or load it in your code, calculate the position of the necessary element and perform an update. I think there are no other options.

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