Updates are handled identically to inserts when using the save method. The only difference is that instead of starting with a new entity, we start with an existing entity.
You can update multiple fields at once using the update method. This is similar to the create method for creating new entities.
There is no need to call save when using the update method.
By default, if you have a key in the struct that doesn't match a property in the entity the update method will fail. If you add the optional argument ignoreNonExistentAttributes set to true, those missing keys are ignored. Now you can pass the rc scope from your submitted form directly into the update method and not worry about any other keys in the rc like event that would cause the method to fail.
Updates can be performed against any number of entities that match a given query.