ADO.NET中的多数据表操作浅析—读取

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-- 发布日期: 2004-08-21
ADO.NET中的多数据表操作浅析—读取

作者:郑佐??????? 2004-8-5

???????? 在开发基于.NET平台的数据库应用程序时,我们一般都会用到DataSet,作为ADO.NET的核心类它为我们提供了强大的功能,而整个看上去就像是放在内存内的一个小型数据库,内部包括了DataTable、DataView、DataRow、DataColumn、Constraint以及DataRelation。当初看到它时真的是有点兴奋。

???????? 下面根据我的一些经验来举例说明在ADO.NET中的多表填充、关联表更新以及多个Command对象执行过程中启用事务的操作。欢迎大家交流,或在Blog上留言。

????????

一、准备工作

???????? 对于NorthWind数据库大家都比较熟悉,所以这里拿它为例,我把Customers(客户表)、Orders(订单表)、Order Details(订单详细表)合起来建立了一个类型化的数据集,类型名称为DatasetOrders,每个表只包括一些字段,下面是在Visual Studio .NET中建立的一个截图:

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图1-1

上面建立了两个关系表示为Customers —> Orders —>Order Details。因为Orders表的OrderID字段为自动增长列,这里把就把它的AutoIncrementSeed和AutoIncrementStep值设置成了-1,这在实际添加订单的过程中可能会比较明显,不过不设也没问题。

????????

二.填充数据集

建立一个窗体程序来演示实际的操作,界面如下:



图2-1

整个应用程序就是一个Form,上面的三个DataGrid分别用来显示相关表的数据,不过他们是互动的。另外的两个单选框用来决定更新数据的方式,两个按钮正如他们的名称来完成相应的功能。

这里我们用一个DataAdapter来完成数据集的填充,执行的存储过程如下:

CREATE PROCEDURE GetCustomerOrdersInfo

AS

SELECT CustomerID,CompanyName,ContactName FROM Customers WHERE CustomerID LIKE 'A%'

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SELECT OrderID,OrderDate,CustomerID FROM Orders? WHERE CustomerID IN

(SELECT CustomerID FROM Customers WHERE CustomerID LIKE 'A%')

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SELECT OrderID,ProductID,UnitPrice,Quantity,Discount FROM [Order Details] WHERE OrderID IN

(SELECT OrderID FROM Orders? WHERE CustomerID IN

(SELECT CustomerID FROM Customers WHERE CustomerID LIKE 'A%'))

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GO

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为了减少数据量,这里只取了CustomerID以’A’开头的数据。

建立DataAccess类来管理窗体同数据层的交互:

using System;

using System.Data;

using System.Data.SqlClient;

using Microsoft.ApplicationBlocks.Data;

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namespace WinformTest

{

???? public class DataAccess

???? {

???????? private string _connstring = "data source=(local);initial catalog=Northwind;uid=csharp;pwd=c#.net2004;";

???????? private SqlConnection _conn;

???????? ///构造函数

public DataAccess()

???????? {

????????????? _conn = new SqlConnection(_connstring);

}

下面的函数完成单个数据适配器来完成数据集的填充,

public void FillCustomerOrdersInfo(DatasetOrders ds)

???? ???? {

????????????? SqlCommand comm = new SqlCommand("GetCustomerOrdersInfo",_conn);

????????????? comm.CommandType = CommandType.StoredProcedure;

????????????? SqlDataAdapter dataAdapter = new SqlDataAdapter(comm);

????????????? dataAdapter.TableMappings.Add("Table","Customers");

????????????? dataAdapter.TableMappings.Add("Table1","Orders");

????????????? dataAdapter.TableMappings.Add("Table2","Order Details");

????????????? dataAdapter.Fill(ds);

???????? }

如果使用SqlHelper来填充那就更简单了,

???????? public void FillCustomerOrdersInfoWithSqlHelper(DatasetOrders ds)

???????? {???????????? SqlHelper.FillDataset(_connstring,CommandType.StoredProcedure,"GetCustomerOrdersInfo",ds,new string[]{"Customers","Orders","Order Details"});

???????? }

叉开话题提一下,Data Access Application Block 2.0中的SqlHelper.FillDataset这个方法超过两个表的填充时会出现错误,其实里面的逻辑是错的,只不过两个表的时候刚好凑巧,下面是从里面截的代码:

private static void FillDataset(SqlConnection connection, SqlTransaction transaction, CommandType commandType,

????????????? string commandText, DataSet dataSet, string[] tableNames,

????????????? params SqlParameter[] commandParameters)

???????? {

????????????? if( connection == null ) throw new ArgumentNullException( "connection" );

????????????? if( dataSet == null ) throw new ArgumentNullException( "dataSet" );

????????????? SqlCommand command = new SqlCommand();

????????????? bool mustCloseConnection = false;

????????????? PrepareCommand(command, connection, transaction, commandType, commandText, commandParameters, out mustCloseConnection );

??? ????????? using( SqlDataAdapter dataAdapter = new SqlDataAdapter(command) )

????????????? {

???????? ????????? if (tableNames != null && tableNames.Length > 0)

?????????????????? {

?????????????????????? string tableName = "Table";

?????????????????????? for (int index=0; index < tableNames.Length; index++)

?????????????????????? {

??????????????????????????? if( tableNames[index] == null || tableNames[index].Length == 0 )

???????????????????????????????? throw new ArgumentException( "The tableNames parameter must contain a list of tables, a value was provided as null or empty string.", "tableNames" );

??????????????????????????? tableName += (index + 1).ToString();//这里出现错误

?????????????????????? }

?????????????????? }

?????????????????? dataAdapter.Fill(dataSet);

?????????????????? command.Parameters.Clear();

????????????? }

????????????? if( mustCloseConnection )

?????????????????? connection.Close();

???????? }

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这里把tableName += (index + 1).ToString();修改成

dataAdapter.TableMappings.Add((index>0)?(tableName+index.ToString()):tableName, tableNames[index]);就能解决问题。

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接下来看看窗体程序的代码:

public class Form1 : System.Windows.Forms.Form

???? {

???????? private DataAccess _dataAccess;

???????? private DatasetOrders _ds;

???????? //……

???????? //构造函数

???????? public Form1()

???????? {

????????????? InitializeComponent();

????????????? _dataAccess = new DataAccess();

????????????? _ds = new DatasetOrders();

????????????? _ds.EnforceConstraints = false; //关闭约束检查,提高数据填充效率

????????????? this.dataGridCustomers.DataSource = _ds;

????????????? this.dataGridCustomers.DataMember = _ds.Customers.TableName;

????????????? this.dataGridOrders.DataSource = _ds;

????????????? this.dataGridOrders.DataMember = _ds.Customers.TableName+"."+_ds.Customers.ChildRelations[0].RelationName;

????????????? this.dataGridOrderDetails.DataSource = _ds;

????????????? this.dataGridOrderDetails.DataMember = _ds.Customers.TableName+"."+_ds.Customers.ChildRelations[0].RelationName+"."+_ds.Orders.ChildRelations[0].RelationName;

???????? }

对于上面的三个表的动态关联,你也可以使用SetDataBinding方法来完成数据的动态绑定,而不是分别指定DataGride的DataSource和DataMemger属性。

this.dataGridCustomers.SetDataBinding(_ds,_ds.Customers.TableName);

this.dataGridOrders.SetDataBinding(_ds,_ds.Customers.TableName+"."+_ds.Customers.ChildRelations[0].RelationName);

this.dataGridOrderDetails.SetDataBinding(_ds,_ds.Customers.TableName+"."+_ds.Customers.ChildRelations[0].RelationName+"."+_ds.Orders.ChildRelations[0].RelationName);

}

数据填充事件处理如下:????????????????????????

private void buttonFillData_Click(object sender, System.EventArgs e)

???????? {

????????????? _ds.Clear();//重新填充数据集

????????????? _dataAccess.FillCustomerOrdersInfo(_ds);

????????????? //_dataAccess.FillCustomerOrdersInfoWithSqlHelper(_ds);

???????? }

执行上面的事件处理函数我们会看到数据显示到对应的DataGrid上,如(图2-1)所示。

如果使用数据读取器获取多表纪录下面是实现的一种方式(参考):

SqlCommand comm = new SqlCommand("GetCustomerOrdersInfo",_conn);

comm.CommandType = CommandType.StoredProcedure;

_conn.Open();

SqlDataReader reader = comm.ExecuteReader();

do

{

???? while(reader.Read())

???? {

???????? Console.WriteLine(reader[0].ToString());//获取数据代码

???? }

}while(reader.NextResult());

Console.ReadLine();

_conn.Close();

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