Modifies an existing document or documents in a collection.
The method can modify specific fields of an existing document or documents or replace an existing document entirely, depending on the update parameter.
By default, the update() method updates a single document. Set the Multi Parameter to update all documents that match the query criteria.
The update() method has the following form:
db.collection.update(
<query>,
<update>,
{
upsert: <boolean>,
multi: <boolean>,
writeConcern: <document>
}
)
