Objects, like rows, are the actual data.Properties, like columns, define the specific pieces of data that every instance of the class should contain.Classes, like tables, model the data you want to represent in your app.The structure of a relational database also mirrors what you already know about classes and objects in Kotlin. Rows contain the actual data that consist of values for each column in the table.Columns define the data that each row in the table contains.Tables define high-level groupings of data you want to represent, such as students and professors. ![]() For example, you might define columns for a student's ID, name, major, and grade.Įach row contains data for a single student, with values for each of the columns.Ī relational database works the same way. If you are familiar with a spreadsheet program like Google Sheets, you are already familiar with a basic analogy for a database.Ī spreadsheet consists of separate data tables, or individual spreadsheets in the same workbook.Įach table consists of columns that define what the data represents and rows that represent individual items with values for each column. ![]() To learn more about the different methods for storing data on Android, refer to the Data and file storage overview. ![]() This unit discusses Room and Preferences Datastore. Note: Android apps have a number of ways to store data, including both internal and external storage. This codelab teaches the fundamentals of SQL-Structured Query Language-which, while not an actual programming language, provides a simple and flexible way to read and modify a SQLite database with just a few lines of code.Īfter you gain a fundamental knowledge of SQL, you'll be prepared to use the Room library to add persistence to your apps later in this unit. SQLite provides a relational database that allows you to represent data in a similar way to how you structure data with Kotlin classes. SQLite is a common way provided by the Android SDK for Android apps to persist data. Persistent data ensures user-generated content isn't lost when the app is closed, or data downloaded from the internet is saved so it doesn't need to be redownloaded later. The Clock app stores your recurring alarms, the Google Maps app saves a list of your recent searches, and the Contacts app lets you add, edit, and remove your contacts' information.ĭata persistence-storing or persisting data on the device-is a big part of Android development. Once loaded, modify the code to add the appropriate data members and methods: package of the apps you use store data directly on the device. Once created the Product.java source file will automatically load into the Android Studio editor. From the popup menu, choose the New -> Java Class option and, in the Create New Class dialog, name the class Product before clicking on the OK button. Within Android Studio, navigate within the Project tool window to app -> java and right-click on the package name. ![]() Essentially, this class can be thought of as representing the database model. Instances of this class can then be created within the activity and database handler and passed back and forth as needed. This is actually a very simple class capable of holding product ID, product name and product quantity values, together with getter and setter methods for accessing these values. In order to implement this interaction in a structured way, a third class will need to be implemented to hold the database entry data as it is passed between the activity and the handler. The database handler will be a subclass of SQLiteOpenHelper and will provide an abstract layer between the underlying SQLite database and the activity class, with the activity calling on the database handler to interact with the database (adding, removing and querying database entries). Once completed, the application will consist of an activity and a database handler class.
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