A good database base class, which facilitates the construction of database operation classes.

Android uses sqlite as a database. sqlite is quite easy to use. Of course, it also encapsulates it. However, I still like to write it using SQL instead of calling android-encapsulated functions, in this way, it can be reused on different platforms.

Code: The following is a base class of a Database. Using this class, you can quickly construct a database operation class. When writing a database, I use trycatch in my experience. This makes it easy to find a problem.

Import android. content. Context;
Import android. database. Cursor;
Import android. database. SQLException;
Import android. database. sqlite. SQLiteDatabase;
Import android. database. sqlite. SQLiteOpenHelper;
Import android. util. Log;

Public abstract class AbstractDBHelper
{
// SQLite database instance
Protected SQLiteDatabase mDb = null;

// Database creation helper
Protected CreateDBHelper mDbHelper = null;

// Obtain the ID of the current database helper class (generally the class name), used for logging and other records
Protected abstract String getTag ();

// Obtain the Database Name
Protected abstract String getDatabaseName ();

/**
* Obtain the database version. The value must be at least 1.
* When the database structure changes, add this value to 1 and the system will automatically call it during initialization.
* The createDBTables and dropDBTables Methods update the database structure.
*/
Protected abstract int getDatabaseVersion ();

// Create an SQL statement for the database table. One element and one statement
Protected abstract String [] createDBTables ();

// Delete the SQL statement of the database table, one element and one statement
Protected abstract String [] dropDBTables ();

// Helper class for internal database creation
Private class CreateDBHelper extends SQLiteOpenHelper
{
Public CreateDBHelper (Context ctx)
{
Super (ctx, getDatabaseName (), null, getDatabaseVersion ());
}
@ Override
Public void onCreate (SQLiteDatabase db)
{
ExecuteBatch (createDBTables (), db );
}
 
@ Override
Public void onUpgrade (SQLiteDatabase db, int oldVersion, int newVersion)
{
Log. w (getTag (), "Upgrading database '" + getDatabaseName () + "'from version" + oldVersion + "to" + newVersion );
ExecuteBatch (dropDBTables (), db );
OnCreate (db );
}
 
// Execute SQL statements in batches
Private void executeBatch (String [] sqls, SQLiteDatabase db)
{
If (sqls = null)
{
Return;
}

Db. beginTransaction ();
Try
{
Int len = sqls. length;
For (int I = 0; I <len; I ++)
{
Db.exe cSQL (sqls [I]);
}
Db. setTransactionSuccessful ();
}
Catch (Exception e)
{
Log. e (getTag (), e. getMessage (), e );
}
Finally
{
Db. endTransaction ();
}
}
}

// Open or create a database with the specified name
Public void open (Context ctx)
{
Log. I (getTag (), "Open database" + getDatabaseName () + "'");
Try
{
MDbHelper = new CreateDBHelper (ctx );
If (mDbHelper! = Null)
{
MDb = mDbHelper. getWritableDatabase ();
}
}
Catch (SQLException e)
{
Log. e ("open", e. getMessage ());
}

}

// Close the database
Public void close ()
{
Try
{
If (mDbHelper! = Null)
{
Log. I (getTag (), "Close databas'" + getDatabaseName () + "'");
MDbHelper. close ();
}
}
Catch (SQLException e)
{
Log. e ("close", e. getMessage ());
}
}
 
// Execute SQL
Protected void executeSQL (String SQL)
{
If (SQL. equals (""))
{
Return;
}

Try
{
MDb.exe cSQL (SQL );
}
Catch (SQLException e)
{
Log. I (getTag (), e. getMessage (), e );
}
}

Protected Cursor Query (String SQL, String [] strArgs)
{
Return mDb. rawQuery (SQL, strArgs );
}
}