Mobile applications that do not need to store at least some amount of persistent data are few and far between. The use of databases is an essential aspect of most applications, ranging from applications that are almost entirely data driven, to those that simply need to store small amounts of data such as the prevailing score of a game.
The importance of persistent data storage becomes even more evident when taking into consideration the somewhat transient lifecycle of the typical Android application. With the ever-present risk that the Android runtime system will terminate an application component to free up resources, a comprehensive data storage strategy to avoid data loss is a key factor in the design and implementation of any application development strategy.
This chapter will provide an overview of the SQLite database management system bundled with the Android operating system, together with an outline of the Android SDK classes that are provided to facilitate persistent SQLite based database storage from within an Android application. Before delving into the specifics of SQLite in the context of Android development, however, a brief overview of databases and SQL will be covered.
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Understanding Database Tables Database
Tables provide the most basic level of data structure in a database. Each database can contain multiple tables and each table is designed to hold information of a specific type. For example, a database may contain a customer table that contains the name, address and telephone number for all the customers of a particular business. The same database may also include a products table used to store the product descriptions with associated product codes for the items sold by the business. Each table in a database is assigned a name that must be unique within that particular database.
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A table name, once assigned to a table in one database, may only be re-used within the context of a different database. 46.2 Introducing Database Schema Database Schema define the characteristics of the data stored in a database table.
For example, the table schema for a customer database table might define that the customer name is a string of no more than 20 characters in length, and that the customer phone number is a numerical data field of a certain format. Schema are also used to define the structure of entire databases and the relationship between the various tables contained in each database.