使用Java更新MongoDB中的特定字段而不是整个文档

Question

I'm using MongoDB 3.2 and MongoDB Java Driver 3.2. In order to update the document I use the following code:

unfetchedEpisodes.stream()
    .forEach(ep -> {
        BasicDBObject updatedFields = new BasicDBObject();
        updatedFields.append("fetchStatus", "IN_PROCESS");

        updateColFields(updatedFields, dbCollection, new ObjectId(ep.get("_id").toString()));
    });

public void updateColFields(BasicDBObject updatedFields, MongoCollection<Document> dbCollection, ObjectId docID) {

    BasicDBObject setQuery = new BasicDBObject();
    setQuery.append("$set", updatedFields);

    BasicDBObject searchQuery = new BasicDBObject("_id", docID);

    dbCollection.updateOne(searchQuery, setQuery);
}

This code works but I'm not sure that this code updates only the specific field (eg fetchStatus ) of the document and not overwrites the whole document.

My question:
Does this code update only the specific field of the document or simply overwrites the whole document ?

Answer 1

It just updates the specified field. The field will be created if it doesn't exist. Other fields remain untouched. According to documentation :

The $set operator replaces the value of a field with the specified value.

and

If the field does not exist, $set will add a new field with the specified value, provided that the new field does not violate a type constraint. If you specify a dotted path for a non-existent field, $set will create the embedded documents as needed to fulfill the dotted path to the field.