Alex Rivera | Logout

In mongoDb, how do you remove an array element by its index?

Asked 2011-01-03T20:58:01.327
116

In the following example, assume the document is in the db.people collection.

How to remove the 3rd element of the interests array by it's index?

{
  "_id" : ObjectId("4d1cb5de451600000000497a"),           
  "name" : "dannie",  
  "interests" : [  
    "guitar",  
    "programming",           
    "gadgets",  
    "reading"  
  ]   
}

This is my current solution: 

var interests = db.people.findOne({"name":"dannie"}).interests;  
interests.splice(2,1)  
db.people.update({"name":"dannie"}, {"$set" : {"interests" : interests}});

Is there a more direct way?

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1 Answer

159

There is no straight way of pulling/removing by array index. In fact, this is an open issue http://jira.mongodb.org/browse/SERVER-1014 , you may vote for it.

The workaround is using $unset and then $pull:

db.lists.update({}, {$unset : {"interests.3" : 1 }}) 
db.lists.update({}, {$pull : {"interests" : null}})

Update: as mentioned in some of the comments this approach is not atomic and can cause some race conditions if other clients read and/or write between the two operations. If we need the operation to be atomic, we could:

  • Read the document from the database
  • Update the document and remove the item in the array
  • Replace the document in the database. To ensure the document has not changed since we read it, we can use the update if current pattern described in the mongo docs
answered 2011-01-03T22:19:38.007

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