Core Data
Core Data is Apple's persistence framework, which is used to persist—store our application's data in a persistent store, which may be memory or a flat file database. It helps us represent our data model in terms of an object graph, establish relationships among objects, and it can also store object graphs on the disk. It also allows us to use the entities of our data model in the form of objects, that is, it maps our data into a form that can be easily stored in a database, such as SQLite, or into a flat file. Also, the Core Data reduces a lot of coding. On using Xcode's templates for Core Data applications, we automatically get the boilerplate code that does several complex tasks such as generating XML files, binary files, SQLite files automatically for us without writing a single code, allowing us to focus on the business logic of our application.
Besides this, Core Data also provides several features that are required in data manipulation, which includes filtering data, querying data, sorting data, establishing relationships with other data, and persisting data in different repositories.
Core Data features
The Core Data framework provides lots of features that include the following:
- Supports migrating and versioning: It means we can modify our data model, that is, entities of the application, whenever desired. The Core Data will replace the older persistent store with the revised data model. This concept is nicely explained with figures in Chapter 11,
- Supports Key-Value Coding (KVC): It is used to store and retrieve data from the managed objects. Core Data provides the methods required for setting and retrieving attribute values from the managed object, respectively. We will be using this feature in our application to display the information of customers and the products sold to them through the table view.
- Tracks the modifications: Core Data keeps track of the modifications performed on managed objects thus allowing us to undo any changes if required. We will be using this feature in our application while modifying the information of a customer or product to know what the earlier value was and what the new value entered for it is.
- Supports lazy loading: It's a situation that arises when all the property values of a managed object are not loaded from the data store and the property values are accessed by the application. In such situations, faulting occurs and the data is retrieved from the store automatically.
- Efficient database retrievals: Core Data queries are optimized for this, though the execution of query is dependent on the data store.
- Multi-threading: Core Data supports multi-threading in an application, that is, more than one thread can be executed in parallel to increase performance. Even some tasks can be performed in the background using a separate thread.
- Inverse relationship: Core Data maintains an inverse relationship for consistency. If we add an object to a relationship, Core Data will automatically take care of adding the correct object to the inverse relationship. Also, if we remove an object from a relationship, Core Data will automatically remove it from the inverse relationship. In our application, we will be using an inverse relationship between the Customer and Product entities, so that if a customer is deleted, the information of all the products purchased by him/her should also be automatically deleted.
- External data repositories: Core Data supports storing objects in external data repositories in different formats.