** ADO.NET ** ** 中的多数据表操作浅析—修改 **
作者：郑佐 ??????? 2004-8-5
** 三、更新数据集 **
首先需要说明的是我这里去掉了 Order Details 表，对两个表的操作只是其中的几个字段。下面是窗体界面：
图 3-1
单选框用来选择不同的更新方法。
在 DataAccess 类中增加两个类成员变量：
???? private SqlDataAdapter _customerDataAdapter; // 客户数据适配器
???? private SqlDataAdapter _orderDataAdapter; // 订单数据适配器
?
customerDataAdapter 在构造函数中的初始化为
// 实例化 _customerDataAdapter
SqlCommand selectCustomerComm = new SqlCommand("GetCustomer",_conn);
selectCustomerComm.CommandType = CommandType.StoredProcedure;
selectCustomerComm.Parameters.Add("@CustomerID",SqlDbType.NChar,5,"CustomerID");
????????
SqlCommand insertCustomerComm = new SqlCommand("AddCustomer",_conn);
insertCustomerComm.CommandType = CommandType.StoredProcedure;
insertCustomerComm.Parameters.Add("@CustomerID",SqlDbType.NChar,5,"CustomerID");
insertCustomerComm.Parameters.Add("@CompanyName",SqlDbType.NVarChar,40,"CompanyName");
insertCustomerComm.Parameters.Add("@ContactName",SqlDbType.NVarChar,30,"ContactName");
?
SqlCommand updateCustomerComm = new SqlCommand("UpdateCustomer",_conn);
updateCustomerComm.CommandType = CommandType.StoredProcedure;
updateCustomerComm.Parameters.Add("@CustomerID",SqlDbType.NChar,5,"CustomerID");
updateCustomerComm.Parameters.Add("@CompanyName",SqlDbType.NVarChar,40,"CompanyName");
updateCustomerComm.Parameters.Add("@ContactName",SqlDbType.NVarChar,30,"ContactName");
?????????????
SqlCommand deleteCustomerComm = new SqlCommand("DeleteCustomer",_conn);
deleteCustomerComm.CommandType = CommandType.StoredProcedure;
deleteCustomerComm.Parameters.Add("@CustomerID",SqlDbType.NChar,5,"CustomerID");
?
_customerDataAdapter = new SqlDataAdapter(selectCustomerComm);
_customerDataAdapter.InsertCommand = insertCustomerComm;
_customerDataAdapter.UpdateCommand = updateCustomerComm;
_customerDataAdapter.DeleteCommand = deleteCustomerComm;
?
上面的代码完全可以用设计器生成，觉得有些东西自己写感觉更好，不过代码还是很多。
对于 _orderDataAdapter 的初始化同上面的差不多，这里我们只看订单增加的处理，下面是存储过程：
CREATE PROCEDURE ? AddOrder
(
???? @OrderID INT OUT,
???? @CustomerID NCHAR(5),
???? @OrderDate DATETIME
)
AS
INSERT INTO Orders
(
???? CustomerID ,
???? OrderDate
)
VALUES
(
???? @CustomerID ,
???? @OrderDate
)
--SELECT @OrderID = @@IDENTITY
SET @OrderID = SCOPE_IDENTITY()
GO
?
OrderID 自动增长值的获取通过输出参数来完成，这个相当不错，如果使用 SqlDataAdapter.RowUpdated 事件来处理那效率会很低。
对 insertOrderComm 对象的定义为：
SqlCommand insertOrderComm = new SqlCommand("AddOrder",_conn);
insertOrderComm.CommandType = CommandType.StoredProcedure;
insertOrderComm.Parameters.Add("@OrderID",SqlDbType.Int,4,"OrderID");
insertOrderComm.Parameters["@OrderID"].Direction = ParameterDirection.Output;
insertOrderComm.Parameters.Add("@OrderDate",SqlDbType.DateTime,8,"OrderDate");
insertOrderComm.Parameters.Add("@CustomerID",SqlDbType.NChar,5,"CustomerID");
?
在实现数据的更新方法之前我们先来明确一些更新逻辑：
对于标记为删除的行，先删除订单表的数据，再删除客户表的数据；
对于标记为添加的行，先添加客户表的数据，再添加订单表的数据。
?
（ 1 ）实现用获取修改过的 DataSet 的副本子集来更新数据的方法。
这也是调用 Xml Web Service 更新数据的常用方法，先来看第一个版本，子集的获取通过 DataSet.GetChangs 方法来完成。
// 使用数据集子集更新数据
public void UpdateCustomerOrders(DatasetOrders ds)
{ ????????????
???? DataSet dsModified = ds.GetChanges(DataRowState.Modified); // 获取修改过的行
???? DataSet dsDeleted = ds.GetChanges(DataRowState.Deleted); // 获取标记为删除的行
???? DataSet dsAdded = ds.GetChanges(DataRowState.Added); // 获取增加的行
???? try
???? { ???
???????? _conn.Open(); // 先添加客户表数据，再添加订单表数据
???????? if (dsAdded != null )
???????? {
????????????? _customerDataAdapter.Update(dsAdded,"Customers");
????????????? _orderDataAdapter.Update(dsAdded,"Orders");
????????????? ds.Merge(dsAdded);
???????? }
???????? if (dsModified != null ) // 更新数据表
???????? {
???????? ???? _customerDataAdapter.Update(dsModified,"Customers");
????????????? _orderDataAdapter.Update(dsModified,"Orders");
????????????? ds.Merge(dsModified);
???????? }
???????? if (dsDeleted != null ) // 先删除订单表数据，再删除客户表数据
???????? {
????????????? _orderDataAdapter.Update(dsDeleted,"Orders");
????????????? _customerDataAdapter.Update(dsDeleted,"Customers");
????????????? ds.Merge(dsDeleted);
???????? } ?????????????????
???? }
???? catch (Exception ex)
???? {
???????? throw new Exception(" 更新数据出错 ",ex);
???? }
???? finally
???? {
???????? if (_conn.State != ConnectionState.Closed)
????????????? _conn.Close();
???? }
}
上面的方法看上去比较清晰，不过效率不会很高，至少中间创建了三个 DataSet ，然后又进行了多次合并。
（ 2 ）另一方法就是引用更新，不创建副本。
相对来说性能会高许多，但是如果用在 Web 服务上传输的数据量会更大 ( 可以结合两个方法进行改进 ) 。具体的实现就是通过 DataTable.Select 方法选择行状态来实现。
// 引用方式更新数据
public void UpdateCustomerOrders(DataSet ds)
{
???? try
???? { ???
???????? _conn.Open();
???????? // 先添加客户表数据，再添加订单表数据 ???? _customerDataAdapter.Update(ds.Tables["Customers"].Select("","",DataViewRowState.Added));
???? _orderDataAdapter.Update(ds.Tables["Orders"].Select("","",DataViewRowState.Added));
???? // 更新数据表
???? _customerDataAdapter.Update(ds.Tables["Customers"].Select("","",DataViewRowState.ModifiedCurrent));
???? _orderDataAdapter.Update(ds.Tables["Orders"].Select("","",DataViewRowState.ModifiedCurrent));
// 先删除订单表数据，再删除客户表数据
???? _orderDataAdapter.Update(ds.Tables["Orders"].Select("","",DataViewRowState.Deleted));
???? _customerDataAdapter.Update(ds.Tables["Customers"].Select("","",DataViewRowState.Deleted)); ???????????
???? }
???? catch (Exception ex)
???? {
???????? throw new Exception(" 更新数据出错 ",ex);
???? }
???? finally
???? {
???????? if (_conn.State != ConnectionState.Closed)
????????????? _conn.Close();
???? }
}
结合上面的两个方法我们可想到调用 Web Service 有更合理的方法来完成。
（ 3 ）使用事务
public void UpdateCustomerOrdersWithTransaction(DataSet ds)
{
???? SqlTransaction trans = null ;
???? try
???? { ???
???????? _conn.Open();
???????? trans = _conn.BeginTransaction();
???????? _customerDataAdapter.DeleteCommand.Transaction = trans;
???????? _customerDataAdapter.InsertCommand.Transaction = trans;
???????? _customerDataAdapter.UpdateCommand.Transaction = trans;
???????? _orderDataAdapter.DeleteCommand.Transaction = trans;
???????? _orderDataAdapter.InsertCommand.Transaction = trans;
???????? _orderDataAdapter.UpdateCommand.Transaction = trans;
???? _customerDataAdapter.Update(ds.Tables["Customers"].Select("","",DataViewRowState.Added));
?????????????????? _orderDataAdapter.Update(ds.Tables["Orders"].Select("","",DataViewRowState.Added));
???? _customerDataAdapter.Update(ds.Tables["Customers"].Select("","",DataViewRowState.ModifiedCurrent));
???? _orderDataAdapter.Update(ds.Tables["Orders"].Select("","",DataViewRowState.ModifiedCurrent));
???? _orderDataAdapter.Update(ds.Tables["Orders"].Select("","",DataViewRowState.Deleted));
???? _customerDataAdapter.Update(ds.Tables["Customers"].Select("","",DataViewRowState.Deleted)); ?
???? ???? trans.Commit();
???? }
???? catch (Exception ex)
???? {
???????? trans.Rollback();
???????? throw new Exception(" 更新数据出错 ",ex);
???? }
???? finally
???? {
???????? if (_conn.State != ConnectionState.Closed)
????????????? _conn.Close();
???? }
}
最后让我们来看看窗体的按钮更新事件的代码：
private void buttonUpdate_Click( object sender, System.EventArgs e)
{
????????????? // 提交编辑数据
???? this .BindingContext[ this ._ds].EndCurrentEdit();
????
???? if (radioButtonRef.Checked == true ) // 引用方式更新
???????? _dataAccess.UpdateCustomerOrders((DataSet)_ds);
???? else if (radioButtonTrans.Checked == true ) // 启用事务更新数据表
???????? _da