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ADO.NET中的多數(shù)據(jù)表操作淺析—讀取
作者：鄭佐??????? 2004-8-5
???????? 在開發(fā)基于.NET平臺(tái)的數(shù)據(jù)庫應(yīng)用程序時(shí)，我們一般都會(huì)用到DataSet，作為ADO.NET的核心類它為我們提供了強(qiáng)大的功能，而整個(gè)看上去就像是放在內(nèi)存內(nèi)的一個(gè)小型數(shù)據(jù)庫，內(nèi)部包括了DataTable、DataView、DataRow、DataColumn、Constraint以及DataRelation。當(dāng)初看到它時(shí)真的是有點(diǎn)興奮。
???????? 下面根據(jù)我的一些經(jīng)驗(yàn)來舉例說明在ADO.NET中的多表填充、關(guān)聯(lián)表更新以及多個(gè)Command對(duì)象執(zhí)行過程中啟用事務(wù)的操作。歡迎大家交流，或在Blog上留言。
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一、準(zhǔn)備工作
???????? 對(duì)于NorthWind數(shù)據(jù)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(xì)表)合起來建立了一個(gè)類型化的數(shù)據(jù)集，類型名稱為DatasetOrders，每個(gè)表只包括一些字段，下面是在Visual Studio .NET中建立的一個(gè)截圖：
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圖1-1
上面建立了兩個(gè)關(guān)系表示為Customers —> Orders —>Order Details。因?yàn)镺rders表的OrderID字段為自動(dòng)增長(zhǎng)列，這里把就把它的AutoIncrementSeed和AutoIncrementStep值設(shè)置成了-1，這在實(shí)際添加訂單的過程中可能會(huì)比較明顯，不過不設(shè)也沒問題。
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二．填充數(shù)據(jù)集
建立一個(gè)窗體程序來演示實(shí)際的操作，界面如下：
圖2-1
整個(gè)應(yīng)用程序就是一個(gè)Form，上面的三個(gè)DataGrid分別用來顯示相關(guān)表的數(shù)據(jù)，不過他們是互動(dòng)的。另外的兩個(gè)單選框用來決定更新數(shù)據(jù)的方式，兩個(gè)按鈕正如他們的名稱來完成相應(yīng)的功能。
這里我們用一個(gè)DataAdapter來完成數(shù)據(jù)集的填充，執(zhí)行的存儲(chǔ)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(shù)據(jù)量，這里只取了CustomerID以’A’開頭的數(shù)據(jù)。
建立DataAccess類來管理窗體同數(shù)據(jù)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(gòu)造函數(shù)
public DataAccess()
???????? {
????????????? _conn = new SqlConnection(_connstring);
}
下面的函數(shù)完成單個(gè)數(shù)據(jù)適配器來完成數(shù)據(jù)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(jiǎn)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(gè)方法超過兩個(gè)表的填充時(shí)會(huì)出現(xiàn)錯(cuò)誤，其實(shí)里面的邏輯是錯(cuò)的，只不過兩個(gè)表的時(shí)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(xiàn)錯(cuò)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(gòu)造函數(shù)
???????? public Form1()
???????? {
????????????? InitializeComponent();
????????????? _dataAccess = new DataAccess();
????????????? _ds = new DatasetOrders();
????????????? _ds.EnforceConstraints = false; //關(guān)閉約束檢查，提高數(shù)據(jù)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(duì)于上面的三個(gè)表的動(dòng)態(tài)關(guān)聯(lián)，你也可以使用SetDataBinding方法來完成數(shù)據(jù)的動(dòng)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(shù)據(jù)填充事件處理如下：????????????????????????
private void buttonFillData_Click(object sender, System.EventArgs e)
???????? {
????????????? _ds.Clear();//重新填充數(shù)據(jù)集
????????????? _dataAccess.FillCustomerOrdersInfo(_ds);
????????????? //_dataAccess.FillCustomerOrdersInfoWithSqlHelper(_ds);
???????? }
執(zhí)行上面的事件處理函數(shù)我們會(huì)看到數(shù)據(jù)顯示到對(duì)應(yīng)的DataGrid上，如（圖2-1）所示。
如果使用數(shù)據(jù)讀取器獲取多表紀(jì)錄下面是實(shí)現(xiàn)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(shù)據(jù)代碼
???? }
}while(reader.NextResult());
Console.ReadLine();
_conn.Close();
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