Removing the array element in mongoDB based on the position of element

问题

Actually I need to remove an element from the array based on its position. Using $pop we can remove element from top or bottom (considering it as a stack. 0th element at top) as explained here.

We can also remove element from array based on the value of the elements in the array using $pull as explained here.

But I need to remove element from the array based on position. So is there any way I can do this.

回答1:

From documentation:

{ $pull : { field : {$gt: 3} } } removes array elements greater than 3

So i suppose that you can do somethig like this for now:

{ $pull : { field : {$gt: 3, $lt: 5} } } // shoud remove elemet in 4 position

Or try update using position operator, i suppose shoud be something like this:

  { $pull : "field.4" } 

  { $pull : {"field.$": 4}}

It is only a suggestion, because i can't test it right now.

Update:

Seems you cant do it right know in one step(there is such bug in jira)

But you can remove using unset element in position and that pull elemets with null value:

{$unset : {"array.4" : 1 }}
{$pull : {"array" : null}}

回答2:

Here's your answer MongoDB pull array element from a collection

To remove specific element from an array of some document first you need to identify this element. For instance I have a document with array and every element of this array is an object:

`{
    "_id" : ObjectId("5140f34888dd50971900002d"),
    "_permissions" : {
        "edit" : [
            {
                "profile_id" : NumberLong(123),
                "comment" : "app/project owner"
            },
            {
                "profile_id" : NumberLong("153579099841888257"),
                "comment" : "project admin"
            },
            {
                "profile_id" : NumberLong("153579095869882369"),
                "comment" : "project admin"
            }
        ],
        "view" : [
            {
                "profile_id" : NumberLong(123),
                "comment" : "app/project owner"
            },
            {
                "profile_id" : NumberLong("153579099841888257"),
                "comment" : "project admin"
            },
            {
                "profile_id" : NumberLong("153579095869882369"),
                "comment" : "project admin"
            }
        ]
    }
}`

So let's remove "profile_id" with "153579099841888257" value from "_permissions.view" array. Here we go

`db.collection.update({_id: ObjectId("5140f34888dd50971900002d")}, {$pull:{"_permissions.view": {"profile_id": NumberLong("153579099841888257")}}});`

I define scope of the object (to make sure id doesn't affect any other first found document)
Identify needed element to pull out: "profile_id" with "153579099841888257" value in the "_permissions.view" array

来源：https://stackoverflow.com/questions/4969768/removing-the-array-element-in-mongodb-based-on-the-position-of-element

标签

arrays

mongodb

pull