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Android




Basics



* What is?

SQLite is an Open Source Database. It requires limited memory (aprox. 250 kbyte).	
SQLite is embeded in every Android device. Doesn't require a setup or administration.


* File system

Accessing database involves accesing the file system. This can be slow. It is recommended to perform 
database operations asynchronously.

If an application creates a database, it is saved by default in /DATA/APP_NAME/databases/FILENAME.

DATA is the path which the Environment.getDataDirectory() method returns.

	%--- MainActivity.java

	String s = Environment.getDataDirectory().toString();
        Toast.makeText(getApplicationContext(), s, Toast.LENGTH_SHORT).show();
		// return /data


* Open Helper

First you must create a subclass of the SQLiteOpenHelper, call the super() specifying the database and 
version, override the two methods:
	onCreate()
	onUpdate()

Both methods receive an	SQLDatabase object as parameter.

It's a good practice to create a separte class for each table.

The database should use an identifier _id for his primary key. Several Android functions rely on this standard.


* SQLDatabas object

SQLDatabase object provides the insert(), update(), delete(), execSQL() methods.

The object ContentValues allows to define key/values.

Queries can be created via the rawQuery() and query(). The latter provides a structured interface for SQL query.


* Cursor

A query returns a cursor object which is the result of the query and points to one row of the result.

moveToFirst(), moveToNext(), isAfterLast(), getString(columnIndex)


http://www.vogella.com/articles/AndroidSQLite/article.html#databasetutorial_intro