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ADO.NET中的多數據表操作淺析—讀取
作者：鄭佐??????? 2004-8-5
???????? 在開發(fā)基于.NET平臺的數據庫應用程序時，我們一般都會用到DataSet，作為ADO.NET的核心類它為我們提供了強大的功能，而整個看上去就像是放在內存內的一個小型數據庫，內部包括了DataTable、DataView、DataRow、DataColumn、Constraint以及DataRelation。當初看到它時真的是有點興奮。
???????? 下面根據我的一些經驗來舉例說明在ADO.NET中的多表填充、關聯表更新以及多個Command對象執(zhí)行過程中啟用事務的操作。歡迎大家交流，或在Blog上留言。
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一、準備工作
???????? 對于NorthWind數據庫大家都比較熟悉，所以這里拿它為例，我把Customers(客戶表)、Orders(訂單表)、Order Details(訂單詳細表)合起來建立了一個類型化的數據集，類型名稱為DatasetOrders，每個表只包括一些字段，下面是在Visual Studio .NET中建立的一個截圖：
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圖1-1
上面建立了兩個關系表示為Customers —> Orders —>Order Details。因為Orders表的OrderID字段為自動增長列，這里把就把它的AutoIncrementSeed和AutoIncrementStep值設置成了-1，這在實際添加訂單的過程中可能會比較明顯，不過不設也沒問題。
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二．填充數據集
建立一個窗體程序來演示實際的操作，界面如下：
圖2-1
整個應用程序就是一個Form，上面的三個DataGrid分別用來顯示相關表的數據，不過他們是互動的。另外的兩個單選框用來決定更新數據的方式，兩個按鈕正如他們的名稱來完成相應的功能。
這里我們用一個DataAdapter來完成數據集的填充，執(zhí)行的存儲過程如下：
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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為了減少數據量，這里只取了CustomerID以’A’開頭的數據。
建立DataAccess類來管理窗體同數據層的交互：
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;
???????? ///構造函數
public DataAccess()
???????? {
????????????? _conn = new SqlConnection(_connstring);
}
下面的函數完成單個數據適配器來完成數據集的填充，
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來填充那就更簡單了，
???????? public void FillCustomerOrdersInfoWithSqlHelper(DatasetOrders ds)
???????? {???????????? SqlHelper.FillDataset(_connstring,CommandType.StoredProcedure,"GetCustomerOrdersInfo",ds,new string[]{"Customers","Orders","Order Details"});
???????? }
叉開話題提一下，Data Access Application Block 2.0中的SqlHelper.FillDataset這個方法超過兩個表的填充時會出現錯誤，其實里面的邏輯是錯的，只不過兩個表的時候剛好湊巧，下面是從里面截的代碼：
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();//這里出現錯誤
?????????????????????? }
?????????????????? }
?????????????????? dataAdapter.Fill(dataSet);
?????????????????? command.Parameters.Clear();
????????????? }
????????????? if( mustCloseConnection )
?????????????????? connection.Close();
???????? }
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這里把tableName += (index + 1).ToString();修改成
dataAdapter.TableMappings.Add((index>0)?(tableName+index.ToString()):tableName, tableNames[index]);就能解決問題。
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接下來看看窗體程序的代碼：
public class Form1 : System.Windows.Forms.Form
???? {
???????? private DataAccess _dataAccess;
???????? private DatasetOrders _ds;
???????? //……
???????? //構造函數
???????? public Form1()
???????? {
????????????? InitializeComponent();
????????????? _dataAccess = new DataAccess();
????????????? _ds = new DatasetOrders();
????????????? _ds.EnforceConstraints = false; //關閉約束檢查，提高數據填充效率
????????????? 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;
???????? }
對于上面的三個表的動態(tài)關聯，你也可以使用SetDataBinding方法來完成數據的動態(tài)綁定，而不是分別指定DataGride的DataSource和DataMemger屬性。
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);
}
數據填充事件處理如下：????????????????????????
private void buttonFillData_Click(object sender, System.EventArgs e)
???????? {
????????????? _ds.Clear();//重新填充數據集
????????????? _dataAccess.FillCustomerOrdersInfo(_ds);
????????????? //_dataAccess.FillCustomerOrdersInfoWithSqlHelper(_ds);
???????? }
執(zhí)行上面的事件處理函數我們會看到數據顯示到對應的DataGrid上，如（圖2-1）所示。
如果使用數據讀取器獲取多表紀錄下面是實現的一種方式（參考）：
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());//獲取數據代碼
???? }
}while(reader.NextResult());
Console.ReadLine();
_conn.Close();
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