Windows应用程序开发入门到精通十三：深入ADO.NET开发—高级数据访问技术 (Level 400)

看了付仲恺的讲座的笔记

private void SimpleConnectionPooling()
{
SqlConnection conn = new SqlConnection("Server=(local);" +
"DataBase=Northwind;" +
"Integrated Security=True;" +
//连接以后，在sql server企业管理器的管理的当前活动的进程信息中，可以显示
"Application Name=Advanced ADO.NET Simple Connection Pooling;" +
//创建连接池，最大5个连接，最少3个连接（会创建3个连接）
"Pooling=true;Max Pool Size=5;Min Pool Size=3"
////连接超时，如果不写这句，默认是15秒
+"Connect timeout = 45;");
// Max Pool Size，Min Pool Size，Connect timeout可以解决超时问题，
//要注意搭配使用。Timeout设长点或者Max Pool Size设大点。
conn.Open();

SqlCommand cmd = new SqlCommand("Select @@version", conn);
string sqlVersion = (string)cmd.ExecuteScalar();

//conn.Close();
MessageBox.Show(sqlVersion,"Sql Version", MessageBoxButtons.OK, MessageBoxIcon.Information);
}

并发处理
DataSet.ContinueUpdateOnError为false（默认）时，如果有并发数据，则抛出异常，此数据后面的数据都不操作。如果为true，则不处理本数据，但继续处理后面的数据，且不抛出异常。
DataRow[] _Collisions=null;
DataSet.ContinueUpdateOnError = true;
DataSet.Update(DataTable);
If(DataTable.HasErrors)
{
_Collisions = DataTable.GetErrors();
}

连接池
连接池对字符串敏感。比如：
“Integrated Security=SSPI;Database=Northwind”
“Integrated Security=SSPI ; Database=Northwind”
只是多了空格，就会建立2个连接池。
Close方法将连接放回连接池。
Dispose方法则直接销毁连接。
尽可能晚的打开连接，尽可能早的关闭连接。

本地事务
public void UpdateOrdersOrderDetails(dsOrdersOrderDetails orders)
{
//TODO: Declare a SqlTransaction variable
SqlTransaction trans=null;//声明事务对象
try
{
//创建一个连接（daOrders是一个DataAdapter）
daOrders.UpdateCommand.Connection=new SqlConnection(GetConnectionString());
daOrders.UpdateCommand.Connection.Open();
daOrders.InsertCommand.Connection = daOrders.UpdateCommand.Connection;
daOrders.DeleteCommand.Connection = daOrders.UpdateCommand.Connection;

//TODO:  Begin the transaction
//创建事务，级别是ReadCommitted
trans= daOrders.UpdateCommand.Connection.
BeginTransaction(IsolationLevel.ReadCommitted);
daOrders.UpdateCommand.Transaction = trans;
daOrders.DeleteCommand.Transaction = trans;
daOrders.InsertCommand.Transaction = trans;
daOrders.Update(orders);
// daOrderDetails是一个DataAdapter
daOrderDetails.UpdateCommand.Connection = daOrders.UpdateCommand.Connection;
daOrderDetails.InsertCommand.Connection = daOrders.UpdateCommand.Connection;
daOrderDetails.DeleteCommand.Connection = daOrders.UpdateCommand.Connection;

//TODO: Participate in the already running transaction
daOrderDetails.UpdateCommand.Transaction = trans;
daOrderDetails.InsertCommand.Transaction = trans;
daOrderDetails.DeleteCommand.Transaction = trans;
daOrderDetails.Update(orders);

//TODO: Commit the transaction
trans.Commit();//提交事务

}
finally
{
//TODO:  Rollback the transaction if it
//       was not committed
if(null!=trans && null!=trans.Connection)
trans.Rollback();

if(null!=daOrders.UpdateCommand.Connection)
{
daOrders.InsertCommand.Connection = null;
daOrders.DeleteCommand.Connection = null;

daOrderDetails.UpdateCommand.Connection = null;
daOrderDetails.InsertCommand.Connection = null;
daOrderDetails.DeleteCommand.Connection = null;

if(ConnectionState.Closed!=daOrders.UpdateCommand.Connection.State)
daOrders.UpdateCommand.Connection.Close();

daOrders.UpdateCommand.Connection.Dispose();
daOrders.UpdateCommand.Connection = null;

}
}
}

分布式高级事务
在中间层添加System.EnterpriseServices.Transaction
[WebMethod(TransactionOption=TransactionOption.Required)]
public void Transaction()
{
//creating a connection with the above WebMethod
//attribute will cause it to automatically enlist with
//the DTC in a transaction
using(SqlConnection conn = new SqlConnection(
"Server=(local);DataBase=Northwind;Integrated Security=True"
+ ";Application Name = Advanced ADO.NET + Cross Database Transactions"
+ ";Pooling=true;Max Pool Size=5;Min Pool Size = 2"
+ ";Connect timeout=30;"))
{

conn.Open();
SqlCommand cmd = new SqlCommand(
"insert into TestTransactions(Value) values ('Northwind')", conn);
cmd.ExecuteNonQuery();
conn.Close();
}

//This connection, even though it's to a different database
//will enlist in the same transaction as above via the DTC
using(SqlConnection conn = new SqlConnection(
"Server=(local);DataBase=pubs;Integrated Security=True"
+ ";Application Name = Advanced ADO.NET + Cross Database Transactions"
+ ";Pooling=true;Max Pool Size=5;Min Pool Size = 2"
+ ";Connect timeout=30;" ))
{
conn.Open();
SqlCommand cmd = new SqlCommand(
"insert into TestTransactions(Value) values ('pubs')", conn);
cmd.ExecuteNonQuery();
conn.Close();
}

//By setting Enlist=false in the connection string below, this
//connection will not belong to the above transaction
using(SqlConnection conn = new SqlConnection(
"Server=(local);DataBase=DataBaseCourse;Integrated Security=True"
+ ";Application Name = Advanced ADO.NET + Cross Database Transactions"
+ ";Pooling=true;Max Pool Size=5;Min Pool Size = 2"
+ ";Connect timeout=30;Enlist=false"//will not automatically enlist in transactions
//注意这里有个Enlist=false，所以不会执行事务操作，数据写入了数据库，没有rollback
))
{
conn.Open();
SqlCommand cmd = new SqlCommand(
"insert into TestTransactions(Value) values ('DataBaseCourse')", conn);
cmd.ExecuteNonQuery();
conn.Close();
}

//We can cause a connection setup like above to
//enlist in the running transation using
//EnlistDistributedTransaction
using(SqlConnection conn = new SqlConnection(
"Server=(local);DataBase=DataBaseCourse;Integrated Security=True"
+ ";Application Name = Advanced ADO.NET + Cross Database Transactions"
+ ";Pooling=true;Max Pool Size=5;Min Pool Size = 2"
+ ";Connect timeout=30;Enlist=false"//will not automatically enlist in transactions
//这里虽然有Enlist=false，但是下面采用了EnlistDistributedTransaction方法，所以还是事务
))
{
conn.Open();
conn.EnlistDistributedTransaction((ITransaction)ContextUtil.Transaction);
SqlCommand cmd = new SqlCommand(
"insert into TestTransactions(Value) values ('Enlisted')", conn);
cmd.ExecuteNonQuery();
conn.Close();
}

//Throwing an exception will cause the transaction to rollback
//抛出异常，导致事务rollback
throw new System.Web.Services.Protocols.SoapException("We blew up...",
System.Web.Services.Protocols.SoapException.ServerFaultCode);
}

可抽取数据访问层
// Form1.cs
Using System.Reflection;
Namespace Demo5
{
[STAThread]
static void Main()
{
Application.Run(new Form1());
}

private void ShowColor(string color)
{
IDAL dal = GetDAL(color);

MessageBox.Show(dal.GetColor(), color);
}

private IDAL GetDAL(string Color)
{
//假设color是green
//取得DALGreen.dll
Assembly asbly = System.Reflection.Assembly.Load("DAL"+Color);
//创建这个类的实例
return (IDAL)asbly.CreateInstance(String.Format("Demo5.DAL{0}", Color));
}

private void btnGreen_Click(object sender, System.EventArgs e)
{
ShowColor("Green");
}

}

// IDAL.cs
namespace Demo5
{
public interface IDAL
{
string GetColor();
}
}

// DALGreen.cs
namespace Demo5
{
public class DALGreen: IDAL
{
public DALGreen()
{
}

public string GetColor()
{
return "Green";
}
}
}