Mongo update all records with a field that's null

Question

How do I update all Mongo documents that have a single field set to 'null', or that doesn't have a value at all?

What I have, but I'm not sure if it's correct:

db.collection.update({name: {$eq: null}}, {$set: {name: 'test'}})

Answer 1

If the name field is not there try:

db.collection.update({"name": {"$exists": false}}, {"$set": {"name": "test"}})

$set will add a new field with the specified value, provided that the new field does not violate a type constraint.

If it is there and null, or does not have a value set:

db.collection.update({"name": null}, {"$set": {"name": "test"}})

---

You can combine both queries using $or as

db.collection.update(
    {
        "$or": [
            { "name": { "$exists": false } }, 
            { "name": null }
        ]
    }, 
    { "$set": { "name": "test" } }
)

---

For MongoDB 3.2 and above, use updateMany() which updates multiple documents within the collection based on the filter:

db.collection.updateMany(
    {
        "$or": [
            { "name": { "$exists": false } }, 
            { "name": null }
        ]
    }, 
    { "$set": { "name": "test" } }
)