Removing empty fields from MongoDB

Question

Normally you would use the following to remove a field from a collection. However the code below does not work for empty ("") fields. How would you go about deleting an empty field in MongoDB?

db.collection.update({}, {$unset: {"": ""}}, {multi:true})

I get the following error message when I try this:

WriteResult({
    "nMatched" : 0,
    "nUpserted" : 0,
    "nModified" : 0,
    "writeError" : {
        "code" : 56,
        "errmsg" : "An empty update path is not valid."
    }
})

How are you defining an "empty field" in your question? Can you edit your question to provide an example? — JohnnyHK, Jun 05 '14 at 18:50
I believe this is the relevant bug: https://jira.mongodb.org/browse/SERVER-12996 — helmy, Jun 05 '14 at 19:41
I have the exact same problem. How was this solved? The accepted answer does not work in latest MongoDB — user1885523, Jul 12 '16 at 21:04
The problem occurred in mongodb 2.6. What it's like in 3.0 and above I don't know. — Jonathan, Jul 13 '16 at 21:46

score 5 · Accepted Answer · answered Jun 05 '14 at 19:21

It looks like empty string keys must only be partially supported by MongoDB.

This isn't as efficient as a multi-update, but it does work to remove those fields in the shell:

db.collection.find().forEach(function(doc) {
    delete doc[''];
    db.collection.save(doc);
});

J.C. Gras · Answer 2 · 2017-08-14T21:33:00.277

5

To do this using the update or updateMany method, you must specify the parameter you want to update, such as name:

db.collection.updateMany({name: ""}, { $unset : { name : 1 }})

edited Aug 14 '17 at 21:33

answered Aug 14 '17 at 21:26

J.C. Gras

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score 2 · Answer 3 · answered Apr 24 '19 at 21:58

2

If you need to delete rows with the field, that is empty, you can use:

db.collection.deleteMany({ 'myField': null})

answered Apr 24 '19 at 21:58

Roman

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score 0 · Answer 4 · answered Jun 22 '23 at 18:31

Updated for mongodb version 4.2+ (db.collection.save is no longer supported)

Empty field keys aren't fully supported by mongodb, and look like they are going to be depreciated.

To get rid of empty field keys

db.collection.find({"":{$exists:true}).forEach(
    (doc)=>{
       delete doc[""];  
       db.collection.replaceOne(doc,doc,{upsert:true})
})

Removing empty fields from MongoDB

4 Answers4