Data Access Application Block提供了通用的数据访问的功能,随着2.0版本的推出有了很大变化。 一.改进 在DAAB1.1里面我们知道Database方法返回或者创建一个DBCommandWrapper对象,而在DAAB2.0里面移除了DBCommandWrapper类,用ADO.NET2.0里面的DBCommand类代替实现类似的功能,这样使得DAAB跟我们的.NET类库的结合更加紧密,回忆一下我们在1.1里面用DBCommandWrapper来访问数据时的代码: Database db = DatabaseFactory.CreateDatabase();
DBCommandWrapper dbCommand = db.GetStoredProcCommandWrapper("GetProductsByCategory"); dbCommand.AddInParameter("CategoryID", DbType.Int32, Category); DataSet productDataSet = db.ExecuteDataSet(dbCommand); 而用了新的DBCommand类之后则变成了: Database db = DatabaseFactory.CreateDatabase();
DbCommand dbCommand = db.GetStoredProcCommand("GetProductsByCategory"); db.AddInParameter(dbCommand, "CategoryID", DbType.Int32, Category); DataSet productDataSet = db.ExecuteDataSet(dbCommand); 数据库连接字符串在我们基于数据库的开发永远是少不了的,但是在DAAB1.1下,它所使用的字符串跟我们在.NET类库中使用的连接字符串却是不能共享的,它们分别保存在不同的位置。而在2.0的Data Access Application Block使用了ADO.NET2.0里面<connectionStrings>配置区,这样带来的一个好处是连接字符串可以在Application Block和自定义的.NET类之间共享使用该配置区,如: <connectionStrings>
<add name="DataAccessQuickStart" providerName="System.Data.SqlClient" connectionString="server=(local)\SQLEXPRESS;database=EntLibQuickStarts;Integrated Security=true" /> </connectionStrings> 在.NET2.0下,泛型编程已经成为了一个核心,而2.0版的DAAB中也新增了一个GenericDatabase对象。DAAB中虽然已经包含了SqlDatabase和OrcaleDatabase,但是如果我们需要使用其他的像DB2等数据库时,就需要用到GenericDatabase,它可以用于任何.NET类库中的数据提供者,包括OdbcProvider和OleDbProvider。 二.使用示例 DAAB2.0的配置非常简单,主要有以下几方面的配置: 配置连接字符串 配置默认数据库 添加相关的命名空间: using Microsoft.Practices.EnterpriseLibrary.Data;
using System.Data; 使用Data Access Application Block进行数据的读取和操作,一般分为三步: 1.创建Database对象 2.提供命令参数,如果需要的话 3.执行命令 下面分别看一下DataAccessQuickStart中提供的一些例子: 执行静态的SQL语句 public string GetCustomerList()
{ // 创建Database对象 Database db = DatabaseFactory.CreateDatabase(); // 使用SQL语句创建DbCommand对象 string sqlCommand = "Select CustomerID, Name, Address, City, Country, PostalCode " + "From Customers"; DbCommand dbCommand = db.GetSqlStringCommand(sqlCommand); StringBuilder readerData = new StringBuilder(); // 调用ExecuteReader方法 using (IDataReader dataReader = db.ExecuteReader(dbCommand)) { while (dataReader.Read()) { // Get the value of the ‘Name‘ column in the DataReader readerData.Append(dataReader["Name"]); readerData.Append(Environment.NewLine); } } return readerData.ToString(); } 执行存储过程并传递参数,返回DataSet public DataSet GetProductsInCategory(int Category)
{ // Create the Database object, using the default database service. The // default database service is determined through configuration. Database db = DatabaseFactory.CreateDatabase(); string sqlCommand = "GetProductsByCategory"; DbCommand dbCommand = db.GetStoredProcCommand(sqlCommand); // Retrieve products from the specified category. db.AddInParameter(dbCommand, "CategoryID", DbType.Int32, Category); // DataSet that will hold the returned results DataSet productsDataSet = null; productsDataSet = db.ExecuteDataSet(dbCommand); // Note: connection was closed by ExecuteDataSet method call return productsDataSet; } 利用DataSet更新数据 public int UpdateProducts()
{ // Create the Database object, using the default database service. The // default database service is determined through configuration. Database db = DatabaseFactory.CreateDatabase(); DataSet productsDataSet = new DataSet(); string sqlCommand = "Select ProductID, ProductName, CategoryID, UnitPrice, LastUpdate " + "From Products"; DbCommand dbCommand = db.GetSqlStringCommand(sqlCommand); string productsTable = "Products"; // Retrieve the initial data db.LoadDataSet(dbCommand, productsDataSet, productsTable); // Get the table that will be modified DataTable table = productsDataSet.Tables[productsTable]; // Add a new product to existing DataSet DataRow addedRow = table.Rows.Add(new object[] {DBNull.Value, "New product", 11, 25}); // Modify an existing product table.Rows[0]["ProductName"] = "Modified product"; // Establish our Insert, Delete, and Update commands DbCommand insertCommand = db.GetStoredProcCommand("AddProduct"); db.AddInParameter(insertCommand, "ProductName", DbType.String, "ProductName", DataRowVersion.Current); db.AddInParameter(insertCommand, "CategoryID", DbType.Int32, "CategoryID", DataRowVersion.Current); db.AddInParameter(insertCommand, "UnitPrice", DbType.Currency, "UnitPrice", DataRowVersion.Current); DbCommand deleteCommand = db.GetStoredProcCommand("DeleteProduct"); db.AddInParameter(deleteCommand, "ProductID", DbType.Int32, "ProductID", DataRowVersion.Current); DbCommand updateCommand = db.GetStoredProcCommand("UpdateProduct"); db.AddInParameter(updateCommand, "ProductID", DbType.Int32, "ProductID", DataRowVersion.Current); db.AddInParameter(updateCommand, "ProductName", DbType.String, "ProductName", DataRowVersion.Current); db.AddInParameter(updateCommand, "LastUpdate", DbType.DateTime, "LastUpdate", DataRowVersion.Current); // Submit the DataSet, capturing the number of rows that were affected int rowsAffected = db.UpdateDataSet(productsDataSet, "Products", insertCommand, updateCommand, deleteCommand, UpdateBehavior.Standard); return rowsAffected; } 通过ID获取记录详细信息 public string GetProductDetails(int productID)
{ // Create the Database object, using the default database service. The // default database service is determined through configuration. Database db = DatabaseFactory.CreateDatabase(); string sqlCommand = "GetProductDetails"; DbCommand dbCommand = db.GetStoredProcCommand(sqlCommand); // Add paramters // Input parameters can specify the input value db.AddInParameter(dbCommand, "ProductID", DbType.Int32, productID); // Output parameters specify the size of the return data db.AddOutParameter(dbCommand, "ProductName", DbType.String, 50); db.AddOutParameter(dbCommand, "UnitPrice", DbType.Currency, 8); db.ExecuteNonQuery(dbCommand); // Row of data is captured via output parameters string results = string.Format(CultureInfo.CurrentCulture, "{0}, {1}, {2:C} ", db.GetParameterValue(dbCommand, "ProductID"), db.GetParameterValue(dbCommand, "ProductName"), db.GetParameterValue(dbCommand, "UnitPrice")); return results; } 以XML格式返回数据 public string GetProductList()
{ // Use a named database instance that refers to a SQL Server database. SqlDatabase dbSQL = DatabaseFactory.CreateDatabase() as SqlDatabase; // Use "FOR XML AUTO" to have SQL return XML data string sqlCommand = "Select ProductID, ProductName, CategoryID, UnitPrice, LastUpdate " + "From Products FOR XML AUTO"; DbCommand dbCommand = dbSQL.GetSqlStringCommand(sqlCommand); XmlReader productsReader = null; StringBuilder productList = new StringBuilder(); try { productsReader = dbSQL.ExecuteXmlReader(dbCommand); // Iterate through the XmlReader and put the data into our results. while (!productsReader.EOF) { if (productsReader.IsStartElement()) { productList.Append(productsReader.ReadOuterXml()); productList.Append(Environment.NewLine); } } } finally { // Close the Reader. if (productsReader != null) { productsReader.Close(); } // Explicitly close the connection. The connection is not closed // when the XmlReader is closed. if (dbCommand.Connection != null) { dbCommand.Connection.Close(); } } return productList.ToString(); } 使用事务 public bool Transfer(int transactionAmount, int sourceAccount, int destinationAccount)
{ bool result = false; // Create the Database object, using the default database service. The // default database service is determined through configuration. Database db = DatabaseFactory.CreateDatabase(); // Two operations, one to credit an account, and one to debit another // account. string sqlCommand = "CreditAccount"; DbCommand creditCommand = db.GetStoredProcCommand(sqlCommand); db.AddInParameter(creditCommand, "AccountID", DbType.Int32, sourceAccount); db.AddInParameter(creditCommand, "Amount", DbType.Int32, transactionAmount); sqlCommand = "DebitAccount"; DbCommand debitCommand = db.GetStoredProcCommand(sqlCommand); db.AddInParameter(debitCommand, "AccountID", DbType.Int32, destinationAccount); db.AddInParameter(debitCommand, "Amount", DbType.Int32, transactionAmount); using (DbConnection connection = db.CreateConnection()) { connection.Open(); DbTransaction transaction = connection.BeginTransaction(); try { // Credit the first account db.ExecuteNonQuery(creditCommand, transaction); // Debit the second account db.ExecuteNonQuery(debitCommand, transaction); // Commit the transaction transaction.Commit(); result = true; } catch { // Rollback transaction transaction.Rollback(); } connection.Close(); return result; } } 三.常见功能 1.创建Database对象 创建一个默认的Database对象 Database dbSvc = DatabaseFactory.CreateDatabase();
默认的数据库在配置文件中: <dataConfiguration defaultDatabase="DataAccessQuickStart" />
创建一个实例Database对象 // Use a named database instance that refers to an arbitrary database type,
// which is determined by configuration information. Database myDb = DatabaseFactory.CreateDatabase("DataAccessQuickStart"); 创建一个具体的类型的数据库对象 // Create a SQL database.
SqlDatabase dbSQL = DatabaseFactory.CreateDatabase("DataAccessQuickStart") as SqlDatabase; 2.创建DbCommand对象 静态的SQL语句创建一个DbCommand Database db = DatabaseFactory.CreateDatabase();
string sqlCommand = "Select CustomerID, LastName, FirstName From Customers"; DbCommand dbCommand = db.GetSqlStringCommand(sqlCommand); 存储过程创建一个DbCommand Database db = DatabaseFactory.CreateDatabase();
DbCommand dbCommand = db.GetStoredProcCommand("GetProductsByCategory"); 3.管理对象 当连接对象打开后,不需要再次连接 Database db = DatabaseFactory.CreateDatabase();
string sqlCommand = "Select ProductID, ProductName From Products"; DbCommand dbCommand = db.GetSqlStringCommand(sqlCommand); // No need to open the connection; just make the call. DataSet customerDataSet = db.ExecuteDataSet(dbCommand); 使用Using及早释放对象 Database db = DatabaseFactory.CreateDatabase();
DbCommand dbCommand = db.GetSqlStringCommand("Select Name, Address From Customers"); using (IDataReader dataReader = db.ExecuteReader(dbCommand)) { // Process results } 4.参数处理 Database类提供了如下的方法,用于参数的处理: AddParameter. 传递参数给存储过程 使用示例如下: Database db = DatabaseFactory.CreateDatabase();
string sqlCommand = "GetProductDetails"; DbCommand dbCommand = db.GetStoredProcCommand(sqlCommand); db.AddInParameter(dbCommand, "ProductID", DbType.Int32, 5); db.AddOutParameter(dbCommand, "ProductName", DbType.String, 50); db.AddOutParameter(dbCommand, "UnitPrice", DbType.Currency, 8); Database db = DatabaseFactory.CreateDatabase();
DbCommand insertCommand = db.GetStoredProcCommand("AddProduct"); db.AddInParameter(insertCommand, "ProductName", DbType.String, "ProductName", DataRowVersion.Current); db.AddInParameter(insertCommand, "CategoryID", DbType.Int32, "CategoryID", DataRowVersion.Current); db.AddInParameter(insertCommand, "UnitPrice", DbType.Currency, "UnitPrice", DataRowVersion.Current); 四.使用场景 DAAB2.0是对ADO.NET2.0的补充,它允许你使用相同的数据访问代码来支持不同的数据库,您通过改变配置文件就在不同的数据库之间切换。目前虽然只提供SQLServer和Oracle的支持,但是可以通过GenericDatabase和ADO.NET 2.0下的DbProviderFactory对象来增加对其他数据库的支持。如果想要编写出来的数据库访问程序具有更好的移植性,则DAAB2.0是一个不错的选择,但是如果您想要针对特定数据库的特性进行编程,就要用ADO.NET了。 参考:Enterprise Libaray –January 2006帮助文档及QuickStart |
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