I was working with Swift programming in MacOS and discovered: if you use the default Core Data database, the first table has an integer primary key hidden under the name Z_PK, and if you add a UUID field, this UUID is saved as a blob datatype in SQLite3. When debugging the program in XCode the Core Data database is saved in the user’s library in a container of the program name/data/Library/Application/program name/program name.sqlite.