本文是关于数据库事务处理及其在安卓系统中的设计模式。它还简要说明了如何处理异常。
这里我们有一个主要的方法，它负责获取数据库实例->启动数据库事务->标记事务成功->提交或回滚事务->关闭数据库。这个主方法有两个子方法，这两个方法都执行一些数据库事务。
1.主要方法定义事务边界。
2.方法连接数据库事务。
3.另一种方法加入数据库事务。
该方法将:
public static void prepareData() throws <Name of the app>AppException
{
try
{
//Get Database Instance
sqliteDatabase = DBUtils.openWritableDatabase();
//Start Database Transaction
DBUtils.beginTransaction(sqliteDatabase);
prepareData1(sqLiteDatabase);
prepareData2(sqLiteDatabase);
//Mark Transaction Successful
setTransactionSuccessful(sqLiteDatabase);
}
catch (Exception exception)
{
String exceptionMessage = "Error in inserting data."
ExceptionManager.processException(AppConstant.ERROR_CODE_1015,
exceptionMessage, exception);
}
finally
{
//Commit or Rollback transaction
endTransaction(sqLiteDatabase);
//Close Database
appDatabase.closeDatabase();
}
}如果我们的要求是从数据库中获取数据，那么我们必须使用openWritableDatabase()方法。
In DbUtil class create openWritableDatabase()/**
* Opens the database
* @return
*/
public static SQLiteDatabase openWritableDatabase()
{
SQLiteDatabase sqliteDatabase = null;
// Opening new database
sqliteDatabase = sqliteOpenHelper.getWritableDatabase();
//Enable Write Ahead Logging
sqliteDatabase.enableWriteAheadLogging();
return sqliteDatabase;
}如果我们的要求是从数据库中读取数据，请使用openReadableDatabase()方法。
In DbUtil class create openReadableDatabase()/**
* Opens the database
* @return
*/
public static SQLiteDatabase openReadableDatabase()
{
SQLiteDatabase sqliteDatabase = null;
// Opening new database
sqliteDatabase = sqliteOpenHelper.getReadableDatabase();
return sqliteDatabase;
}
这个方法用于以独占模式开始我们的事务，当父事务完成时，所有子事务都将被回滚或提交。
In DbUtils class create beginTransaction() method:public static void beginTransaction(SQLiteDatabase sqLiteDatabase)
{
try
{
if(sqLiteDatabase != null)
{
sqLiteDatabase.beginTransaction();
}
}
catch(Exception exception)
{
//Consume Exception
}
}setTransactionSuccessful(SqLietDatabaSe SqLietDatabaSe)方法用于标记我们的事务成功。所有与数据库相关的任务只能在beginTransaction()方法和SetTransactionSuccessful(SqliteDatabaSe)方法之间完成。不要在SetTransactionSuccessful(SqliteDatabaSe)方法和end Transaction(SqliteDatabaSe SqliteDatabaSe)方法之间执行任何与数据库相关的任务。
In DbUtils class createsetTransactionSuccessful(SQLiteDatabase sqliteDatabase) :public static void setTransactionSuccessful(SQLiteDatabase sqLiteDatabase)
{
try
{
if(sqLiteDatabase != null)
{
sqLiteDatabase.setTransactionSuccessful();
}
}
catch(Exception exception)
{
//Consume Exception
}
}此方法用于提交或回滚我们的数据库事务。如果我们的事务被setTransactionSuccessful()方法标记为成功，那么我们的事务将被提交，否则所有更改都将回滚。
In DbUtils class create endTransaction(SQLiteDatabase sqLiteDatabase) method :public static void endTransaction(SQLiteDatabase sqLiteDatabase)
{
try
{
if(sqLiteDatabase != null)
{
sqLiteDatabase.endTransaction();
}
}
catch(Exception exception)
{
//Consume Exception
}
} //Close Database
appDatabase.closeDatabase();这是prepareData()方法的子事务，这里SQLiteDatabase对象必须从父事务方法传递。
private static void prepareData1(SQLiteDatabase sqLiteDatabase)
throws <Name of the app>AppException
{
ContentValues contentValues = null;
long rowId = 0;
try
{
//Prepare ContentValues object
contentValues = new ContentValues();
//Execute Query
rowId = sqLiteDatabase.insertOrThrow("Table Name", null, contentValues);
//If rowId is -1 then this means that Row was not inserted.
//Something went wrong. Throw Exception
if (rowId == -1)
{
String exceptionMessage = "Error in inserting Data. Row Id is -1.";
throw new <Name of the App>AppException
(AppConstant.ERROR_CODE_1011, exceptionMessage);
}
}
catch (Exception exception)
{
//Handle Exception
String exceptionMessage = "Error in inserting Data.";
int errorCode = AppConstant.ERROR_CODE_8012;
ExceptionManager.dispatchExceptionDetails(errorCode, message, exception);
}在这里，我们将数据插入数据库，在执行查询之后，我们必须检查我们的数据是否被插入。如果我们的数据没有插入异常。
//Execute Query
rowId = sqLiteDatabase.insertOrThrow("Table Name", null, contentValues);
//If rowId is -1 then this means that Row was not inserted.
//Something went wrong. Throw Exception
if (rowId == -1)
{
String exceptionMessage = "Error in inserting Data. Row Id is -1.";
throw new <Name of the App>AppException
(AppConstant.ERROR_CODE_1011, exceptionMessage);
}catch (Exception exception)
{
//Handle Exception
String exceptionMessage = "Error in inserting Data.";
int errorCode = AppConstant.ERROR_CODE_8012;
ExceptionManager.dispatchExceptionDetails(errorCode, message, exception);
}方法用于抛出或创建异常对象。
public static void dispatchExceptionDetails(int exceptionCode, String exceptionMessage, Exception exceptionObject) throws <Name of the App>AppException
{
if(exceptionObject instanceof AppException)
{
throw (AppException) exceptionObject;
}
else
{
//Log Exception details
logException(exceptionCode, exceptionMessage, exceptionObject);
//Throw Exception
throw new <Name of the App>AppException(exceptionCode, exceptionMessage);
}
}private static void prepareData2(SQLiteDatabase sqLiteDatabase)
throws <Name of the app>AppException
{
ContentValues contentValues = null;
long rowId = 0;
try
{
contentValues = new ContentValues();
//Prepare ContentValues object
rowId = sqLiteDatabase.insertOrThrow("Table Name", null, contentValues);
//If rowId is -1 then this means that Row was not inserted.
//Something went wrong. Throw Exception
if (rowId == -1)
{
String exceptionMessage = "Error in inserting Data. Row Id is -1.";
throw new <Name of the App>AppException
(AppConstant.ERROR_CODE_1013, exceptionMessage);
}
}
catch (Exception exception)
{
//Handle Exception
String exceptionMessage = "Error in inserting Data.";
int errorCode = AppConstant.ERROR_CODE_8012;
ExceptionManager.dispatchExceptionDetails(errorCode, message, exception);
}
}