ADO.NET使用方法和技巧
来源：网络时间：2011-06-23
bool CheckProductWithReader( int ProductID )
{
using( SqlConnection conn = new SqlConnection(
"server=(local);Integrated Security=SSPI;database=northwind") )
{
SqlCommand cmd = new SqlCommand("CheckProductExistsWithCount", conn );
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.Add("@ProductID", ProductID );
cmd.Parameters["@ProductID"].Direction = ParameterDirection.Input;
conn.Open();
using( SqlDataReader reader = cmd.ExecuteReader(
CommandBehavior.SingleResult ) )
{
if( reader.Read() )
{
return (reader.GetInt32(0) > 0);
}
return false;
}
}
上述代码采用了以下存储过程。
CREATE PROCEDURE CheckProductExistsWithCount
@ProductID int
AS
SELECT COUNT(*) FROM Products
WHERE ProductID = @ProductID
GO
如何编写 ADO.NET 手动事务处理代码
以下代码显示了如何充分利用 SQL Server .NET 数据提供程序所提供的事务处理支持，通过事务来保护资金转帐操作。该操作在同一数据库中的两个帐户之间转移资金。
public void TransferMoney( string toAccount, string fromAccount, decimal amount )
{
using ( SqlConnection conn = new SqlConnection(
"server=(local);Integrated Security=SSPI;database=SimpleBank" ) )
{
SqlCommand cmdCredit = new SqlCommand("Credit", conn );
cmdCredit.CommandType = CommandType.StoredProcedure;
cmdCredit.Parameters.Add( new SqlParameter("@AccountNo", toAccount) );
cmdCredit.Parameters.Add( new SqlParameter("@Amount", amount ));
SqlCommand cmdDebit = new SqlCommand("Debit", conn );
cmdDebit.CommandType = CommandType.StoredProcedure;
cmdDebit.Parameters.Add( new SqlParameter("@AccountNo", fromAccount) );
cmdDebit.Parameters.Add( new SqlParameter("@Amount", amount ));
conn.Open();
// Start a new transaction
using ( SqlTransaction trans = conn.BeginTransaction() )
{
// Associate the two command objects with the same transaction
cmdCredit.Transaction = trans;
cmdDebit.Transaction = trans;
try
{
cmdCredit.ExecuteNonQuery();
cmdDebit.ExecuteNonQuery();
// Both commands (credit and debit) were successful
trans.Commit();
}
catch( Exception ex )
{
// transaction failed
trans.Rollback();
// log exception details . . .
throw ex;
}
}
}
}
如何使用 Transact-SQL 执行事务处理
以下存储过程阐明了如何在 Transact-SQL 存储过程内部执行事务性资金转帐操作。
CREATE PROCEDURE MoneyTransfer
@FromAccount char(20),
@ToAccount char(20),
@Amount money
AS
BEGIN TRANSACTION
-- PERFORM DEBIT OPERATION
UPDATE Accounts
SET Balance = Balance - @Amount
WHERE AccountNumber = @FromAccount
IF @@RowCount = 0
BEGIN
RAISERROR('Invalid From Account Number', 11, 1)
GOTO ABORT
END
DECLARE @Balance money
SELECT @Balance = Balance FROM ACCOUNTS
WHERE AccountNumber = @FromAccount
IF @BALANCE < 0
BEGIN
RAISERROR('Insufficient funds', 11, 1)
GOTO ABORT
END
-- PERFORM CREDIT OPERATION
UPDATE Accounts
SET Balance = Balance + @Amount
WHERE AccountNumber = @ToAccount
IF @@RowCount = 0
BEGIN
RAISERROR('Invalid To Account Number', 11, 1)
GOTO ABORT
END
COMMIT TRANSACTION
RETURN 0
ABORT:
ROLLBACK TRANSACTION
GO
该存储过程使用 BEGIN TRANSACTION、COMMIT TRANSACTION 和 ROLLBACK TRANSACTION 语句来手动控制该事务。
如何编写事务性 .NET 类
以下示例代码显示了三个服务性 .NET 托管类，这些类经过配置以执行自动事务处理。每个类都使用 Transaction 属性进行了批注，该属性的值确定是否应该启动新的事务流，或者该对象是否应该共享其直接调用方的事务流。这些组件协同工作来执行银行资金转帐任务。Transfer 类被使用 RequiresNew 事务属性进行了配置，而 Debit 和 Credit 被使用 Required 进行了配置。结果，所有这三个对象在运行时都将共享同一事务。
using System;
using System.EnterpriseServices;
[Transaction(TransactionOption.RequiresNew)]
public class Transfer : ServicedComponent
{
[AutoComplete]
public void Transfer( string toAccount,
string fromAccount, decimal amount )
{
try
{
// Perform the debit operation
Debit debit = new Debit();
debit.DebitAccount( fromAccount, amount );
// Perform the credit operation
Credit credit = new Credit();
credit.CreditAccount( toAccount, amount );
}
catch( SqlException sqlex )
{
// Handle and log exception details
// Wrap and propagate the exception
throw new TransferException( "Transfer Failure", sqlex );
}
}
}
[Transaction(TransactionOption.Required)]
public class Credit : ServicedComponent
{
[AutoComplete]
public void CreditAccount( string account, decimal amount )
{
try
{
using( SqlConnection conn = new SqlConnection(
"Server=(local); Integrated Security=SSPI"; database="SimpleBank") )
{
SqlCommand cmd = new SqlCommand("Credit", conn );
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.Add( new SqlParameter("@AccountNo", account) );
cmd.Parameters.Add( new SqlParameter("@Amount", amount ));
conn.Open();
cmd.ExecuteNonQuery();
}
}
}catch( SqlException sqlex ){
// Log exception details here
throw; // Propagate exception
}
}
[Transaction(TransactionOption.Required)]
public class Debit : ServicedComponent
{
public void DebitAccount( string account, decimal amount )
{
try
{
using( SqlConnection conn = new SqlConnection(
"Server=(local); Integrated Security=SSPI"; database="SimpleBank") )
{
SqlCommand cmd = new SqlCommand("Debit", conn );
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.Add( new SqlParameter("@AccountNo", account) );
cmd.Parameters.Add( new SqlParameter("@Amount", amount ));
conn.Open();
cmd.ExecuteNonQuery();
}
}
catch (SqlException sqlex)
{
// Log exception details here
throw; // Propagate exception back to caller
}
}
}
