使用同步数据库操作

同步执行和异步执行的主要差异在于：在同步模式下，以单个步骤系列的形式编写代码。相反，在异步代码中，注册事件侦听器，并经常在侦听器方法之间分配操作。当在 同步执行模式 下连接数据库时，可以在单个代码块中连续执行一系列数据库操作。以下示例对此技术进行了演示：

// Include AIRAliases.js to use air.* shortcuts 
     
var conn = new air.SQLConnection(); 
     
// The database file is in the application storage directory 
var folder = File.applicationStorageDirectory; 
var dbFile = folder.resolvePath("DBSample.db"); 
     
// open the database 
conn.open(dbFile, air.OpenMode.UPDATE); 
     
// start a transaction 
conn.begin(); 
     
// add the customer record to the database 
var insertCustomer = new air.SQLStatement(); 
insertCustomer.sqlConnection = conn; 
insertCustomer.text = 
    "INSERT INTO customers (firstName, lastName) " +  
    "VALUES ('Bob', 'Jones')"; 
insertCustomer.execute(); 
     
var customerId = insertCustomer.getResult().lastInsertRowID; 
     
// add a related phone number record for the customer 
var insertPhoneNumber = new air.SQLStatement(); 
insertPhoneNumber.sqlConnection = conn; 
insertPhoneNumber.text =  
    "INSERT INTO customerPhoneNumbers (customerId, number) " +  
    "VALUES (:customerId, '800-555-1234')"; 
insertPhoneNumber.parameters[":customerId"] = customerId; 
insertPhoneNumber.execute(); 
     
// commit the transaction 
conn.commit();

如您所看到的，不管使用的是同步执行还是异步执行，都调用相同的方法来执行数据库操作。两种方法的主要差异在于：执行一个依赖于另一个操作的操作和处理错误。

使用同步执行模式时，无需编写侦听事件的代码来确定操作完成的时间。相反，可以假定如果一个代码行中的操作成功完成，则继续执行下一代码行。因此，要执行一个依赖于另一个操作成功的操作，只需在紧随它所依赖的操作之后编写相关代码即可。例如，要为应用程序编码以开始事务，可执行 INSERT 语句，检索已插入行的主键，将该主键插入到不同表的其他行中，最后提交事务，可以将代码全部编写为一系列语句。以下示例对这些操作进行了演示：

// Include AIRAliases.js to use air.* shortcuts 
     
var conn = new air.SQLConnection(); 
     
// The database file is in the application storage directory 
var folder = File.applicationStorageDirectory; 
var dbFile = folder.resolvePath("DBSample.db"); 
     
// open the database 
conn.open(dbFile, air.OpenMode.UPDATE); 
     
// start a transaction 
conn.begin(); 
     
// add the customer record to the database 
var insertCustomer = new air.SQLStatement(); 
insertCustomer.sqlConnection = conn; 
insertCustomer.text = 
    "INSERT INTO customers (firstName, lastName) " +  
    "VALUES ('Bob', 'Jones')"; 
insertCustomer.execute(); 
     
var customerId = insertCustomer.getResult().lastInsertRowID; 
     
// add a related phone number record for the customer 
var insertPhoneNumber = new air.SQLStatement(); 
insertPhoneNumber.sqlConnection = conn; 
insertPhoneNumber.text =  
    "INSERT INTO customerPhoneNumbers (customerId, number) " +  
    "VALUES (:customerId, '800-555-1234')"; 
insertPhoneNumber.parameters[":customerId"] = customerId; 
insertPhoneNumber.execute(); 
     
// commit the transaction 
conn.commit();

在同步执行模式下，不侦听错误事件来确定操作是否已失败。相反，将可能触发错误的任何代码括在一组 try..catch..finally 代码块中。将引发错误的代码包装在 try 块中。在单独的 catch 块中，编写响应每种类型的错误时要执行的操作。在 finally 块中放置不管成功还是失败（例如，关闭不再需要的数据库连接）都希望始终执行的任何代码。以下示例演示如何使用 try..catch..finally 块进行错误处理。它建立在前面示例的基础之上，添加了错误处理代码：

// Include AIRAliases.js to use air.* shortcuts 
     
var conn = new air.SQLConnection(); 
     
// The database file is in the application storage directory 
var folder = File.applicationStorageDirectory; 
var dbFile = folder.resolvePath("DBSample.db"); 
     
// open the database 
conn.open(dbFile, air.SQLMode.UPDATE); 
     
// start a transaction 
conn.begin(); 
     
try 
{ 
    // add the customer record to the database 
    var insertCustomer = new air.SQLStatement(); 
    insertCustomer.sqlConnection = conn; 
    insertCustomer.text = 
        "INSERT INTO customers (firstName, lastName)" +  
        "VALUES ('Bob', 'Jones')"; 
     
    insertCustomer.execute(); 
     
    var customerId = insertCustomer.getResult().lastInsertRowID; 
     
    // add a related phone number record for the customer 
    var insertPhoneNumber = new air.SQLStatement(); 
    insertPhoneNumber.sqlConnection = conn; 
    insertPhoneNumber.text =  
        "INSERT INTO customerPhoneNumbers (customerId, number)" +  
        "VALUES (:customerId, '800-555-1234')"; 
    insertPhoneNumber.parameters[":customerId"] = customerId; 
     
    insertPhoneNumber.execute(); 
     
    // if we've gotten to this point without errors, commit the transaction 
    conn.commit(); 
} 
catch (error) 
{ 
    // rollback the transaction 
    conn.rollback(); 
}