ADO.NET中的多數據表操作淺析—讀取

作者：鄭佐??????? 2004-8-5

???????? 在開發基于.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關聯，你也可以使用SetDataBinding方法來完成數據的動態綁定，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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