Removing empty fields from MongoDB

To remove empty fields from MongoDB documents, use updateMany() with the $unset operator. This operation identifies documents with empty string values and removes those fields entirely.

Syntax

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

Sample Data

Let us create a collection with documents containing empty fields ?

db.removeEmptyFieldsDemo.insertMany([
    { "StudentName": "" },
    { "StudentName": "Chris" },
    { "StudentName": "" },
    { "StudentName": "Robert" }
]);

{
    "acknowledged": true,
    "insertedIds": [
        ObjectId("5ce92b9578f00858fb12e919"),
        ObjectId("5ce92b9878f00858fb12e91a"),
        ObjectId("5ce92b9c78f00858fb12e91b"),
        ObjectId("5ce92ba078f00858fb12e91c")
    ]
}

View Current Documents

db.removeEmptyFieldsDemo.find();

{ "_id": ObjectId("5ce92b9578f00858fb12e919"), "StudentName": "" }
{ "_id": ObjectId("5ce92b9878f00858fb12e91a"), "StudentName": "Chris" }
{ "_id": ObjectId("5ce92b9c78f00858fb12e91b"), "StudentName": "" }
{ "_id": ObjectId("5ce92ba078f00858fb12e91c"), "StudentName": "Robert" }

Remove Empty Fields

Use updateMany() to remove all empty StudentName fields ?

db.removeEmptyFieldsDemo.updateMany(
    { "StudentName": "" },
    { $unset: { "StudentName": 1 } }
);

{ "acknowledged": true, "matchedCount": 2, "modifiedCount": 2 }

Verify Results

db.removeEmptyFieldsDemo.find();

{ "_id": ObjectId("5ce92b9578f00858fb12e919") }
{ "_id": ObjectId("5ce92b9878f00858fb12e91a"), "StudentName": "Chris" }
{ "_id": ObjectId("5ce92b9c78f00858fb12e91b") }
{ "_id": ObjectId("5ce92ba078f00858fb12e91c"), "StudentName": "Robert" }

Conclusion

The $unset operator with updateMany() effectively removes empty string fields from MongoDB documents. Documents with empty fields will have those fields completely removed, while documents with valid values remain unchanged.