Reverse array field in MongoDB

Question

I have a collection with a location field that was entered in the wrong order:

location: [38.7633698, -121.2697997]

When I try to place a 2

Answer 1

Starting from MongoDB 3.4 we can use the $reverseArray operator to do this beautifully.

Reverse the array:

db.collection.aggregate(
    [ 
        { "$project": { "location": { "$reverseArray": "$location" } } }
    ]
)

which yields:

{
    "_id" : ObjectId("576fdc687d33ed2f37a6d527"), 
    "location" : [ -121.2697997, 38.7633698 ] 
}

Update all documents

To update all the documents in your collection, you have a couple of options.

The first is to add a $out stage to your pipeline and replace the old collection. In this case, you will need to explicitly include all the other field in the $projection stage. The $out stage look like this:

{ "$out": "collection" }

Answer 2

db.loc.find().forEach(function (doc) {
    var loc = [ doc.location[1], doc.location[0] ]; 
    db.loc.update(doc, { $set: { location: loc } });
})