Removing undefined from MongoDB array

Question

I have added undefined values to array using script performed on a server side (Mongo version - 3.4.10).

Let's say I have document like

{
   "array" : ["a","b", undefined]
}

and I want to remove undefined element.

When I query it like this

find({"array" :  {$elemMatch : {$in : [null], $exists : true} }})

It returns above document - Mongo treats null and undefined as equal.

However, below update query is not removing element as expected (works fine for nulls)

update({} ,{ $pull : {"array" : {$in : [null]} }}, {multi : true})

It is also not possible to use undefined as math expression

InMatchExpression equality cannot be undefined

Question: How do you remove elements in such a situation?

Have you tried db.collection.updateMany({}, {"$pull": { "array": undefined }});? — chridam
– chridam, Commented Mar 23, 2018 at 11:48

Rahul Raj · Accepted Answer · 2018-03-24 04:18:37Z

4

db.collection.update(
 {},
 {$pull: {"address.coord":{$type: 6}}},
 {multi:true}

)

Refer the type & pull operators for more details. It will remove all the undefined matches as per your requirement. If your document structure have nested arrays, use $[] positional operators.

answered Mar 24, 2018 at 4:18

Rahul Raj

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