The DataStore Models provides two methods to save data;
save() generates a primary key (in this case, an
id), if one is not provided.
The DataStore provides a
saveOrUpdate method to use for upserts.
If the primary key(in this case an
id) is provided, the DataStore will
try to update the existing document if it exists, if it does not exist
or no primary key was provided, the DataStore saves the data as a new document.