Cocoaphony

For those of you familiar with SQL and coming to Core Data, you probably want to separate the concept of “database” into the two kinds we’re discussing here. There are relational databases, which is what you’re probably used to, and object databases, which is what Core Data provides. Core Data happens to implement its object database on top of a relational database (SQLite), but that is a opaque implementation detail.

In a relational database, the key actions are the select and the transaction. In the select, you ask the database to form itself into a collection of columns (joins are just a fancy way of doing that), filter and sort itself according to some set of rules, and then return you a linear collection of rows. In the transaction, you inform the system that you are beginning a transaction, instruct the database to perform a series of transformations, and then commit or roll-back the transaction. It’s a great model, but Core Data doesn’t look much like it. Read more…