Evjen c07.tex V2 - 01/28/2008 2:01pm Page 375 Chapter 7: Data Binding in ASP.NET 3.5 Summary In this chapter, you examined data binding in ASP.NET. The introduction of data source controls such as the LinqDataSource control, SqlDataSource control, or the XmlDataSource control makes querying and displaying data from any number of data sources an almost trivial task. Using the data source controls’ own wizards, you learned how easy it is to generate powerful data access functionality with almost no code required. You examined how even a beginning developer can easily combine the data source controls with the GridView, ListView, and DetailsView controls to create powerful data manipulation applications with a minimal amount of coding. You saw how ASP.NET includes a multitude of controls that can be data-bound, specifically examining how, since ASP.NET 1.0/1.1, many controls have been enhanced, and examining the features of the data bound controls that are included in the ASP.NET toolbox, such as the GridView, TreeView, ListView, and Menu controls, the new FormView control. Finally, you looked at how the inline data-binding syntax has been improved and strengthened with the addition of the XML-specific data-binding expressions. 375 Evjen c08.tex V2 - 01/28/2008 2:05pm Page 377 Data Management with ADO.NET This chapter provides information on programming with the data management features that are part of ADO.NET, a key component of the .NET Framework and of your ASP.NET development. The discussion begins with the basics of ADO.NET and later dives into the ways you can use various features that make up ADO.NET to manage data contained in a relational database. ADO.NET, first introduced in version 1.0 of the .NET Framework, provided an e xtensive array of features to handle live data in a connected mode or data that is disconnected from its underlying data store. ADO.NET 1.0 was primarily developed to address two specific problems in getting at data. The first had to do with the user’s need to access data once and to iterate through a collection of data in a single instance. This need often arose in Web application development. ADO.NET addresses a couple of the most common data-access strategies that are used for applica- tions today. When classic ADO was developed, many applications could be connected to the data store almost indefinitely. Today, with the explosion of the Internet as the means of data communi- cation, a new data technology is required to make data accessible and updateable in a disconnected architecture. The first of these common data-access scenarios is one in which a user must locate a collection of data and iterate through this data a single time. This is a popular scenario for Web pages. When a request for data from a Web page that you have created is received, you can simply fill a table with data from a data store. In this case, you go to the data store, grab the data that you want, send the data across the wire, and then populate the table. In this scenario, the goal is to get the data in place as fast as possible. The second way to work with data in this disconnected architecture is to grab a collection of data and use this data separately from the data store itself. This could be on the server or even on the client. Although the data is disconnected, you want the ability to keep the data (with all of its tables and relations in place) on the client side. Classic ADO data was represented by a single table that you could iterate through. ADO.NET, however, can be a reflection of the data store itself, with tables, columns, rows, and relations all in place. When you are done with the client-side copy of the data, Evjen c08.tex V2 - 01/28/2008 2:05pm Page 378 Chapter 8: Data Management with ADO.NET you can persist the changes that you made in the local copy of data directly back into the data store. The technology that gives you this capability is the DataSet, which will be covered shortly. Although classic ADO was geared for a two-tiered environment (client-server), ADO.NET addresses a multi-tiered environment. ADO.NET is easy to work with because it has a unified programming model. This unified programming model makes working with data on the server the same as working with data on the client. Because the models are the same, you find yourself more productive when working with ADO.NET. Basic ADO.NET Features This chapter begins with a quick look at the basics of ADO.NET and then provides an overview of basic ADO.NET capabilities, namespaces, and classes. It also reviews how to work with the Connection , Command , DataAdapter , DataSet ,and DataReader objects. Common ADO.NET Tasks Before jumping into the depths of ADO.NET, step back and make sure that you understand some of the common tasks you might perform programmatically within ADO.NET. This next section looks at the process of selecting, inserting, updating, and deleting data. The following example makes use of the Northwind.mdf SQL Server Express Database file. To get this database, please search for ‘‘Northwind and pubs Sample Databases for SQL Server 2000’’. You can find this link at www.microsoft.com/downloads/details.aspx?familyid=06616212-0356-46a0- 8da2-eebc53a68034&displaylang=en . Once installed, you will find the Northwind.mdf file in the C:\ SQL Server 2000 Sample Databases directory. To add this database to your ASP.NET application, create an App_Data folder within your project (if it isn’t already there) and right-click on the folder and select Add Existing Item. From the provided dialog box, you are then able to browse to the location of the Northwind.mdf file that you just installed. If you are having trouble getting permissions to work with the database, make a data connection to the file from the Visual Studio Server Explorer by right-clicking on the Data Connections node and selecting Add N ew Connection from the provided menu. You will be asked to be made the appropriate user of the database. ThenVS will make the appropriate changes on your behalf for this to occur. Selecting Data After the connection to the data source is open and ready to use, you probably want to read the data from the data source. If you do not want to manipulate the data, but simply to read it o r transfer it from one spot to another, you use the DataReader class. In the following example (Listing 8-1), you use the GetCompanyNameData() function to provide a list of company names from the SQL Northwind database. Listing 8-1: Reading the data from a SQL database using the DataReader class VB Imports Microsoft.VisualBasic Imports System.Collections.Generic Continued 378 Evjen c08.tex V2 - 01/28/2008 2:05pm Page 379 Chapter 8: Data Management with ADO.NET Imports System.Data Imports System.Data.SqlClient Public Class SelectingData Public Function GetCompanyNameData() As List(Of String) Dim conn As SqlConnection Dim cmd As SqlCommand Dim cmdString As String = "Select CompanyName from Customers" conn = New SqlConnection("Data Source=. \ SQLEXPRESS;AttachDbFilename= |DataDirectory| \ NORTHWND.MDF;Integrated Security=True; User Instance=True") ’ Put this string on one line in your code cmd = New SqlCommand(cmdString, conn) conn.Open() Dim myReader As SqlDataReader Dim returnData As List(Of String) = New List(Of String) myReader = cmd.ExecuteReader(CommandBehavior.CloseConnection) While myReader.Read() returnData.Add(myReader("CompanyName").ToString()) End While Return returnData End Function End Class C# using System.Data; using System.Data.SqlClient; using System.Collections.Generic; public class SelectingData { public List < string > GetCompanyNameData() { SqlConnection conn; SqlCommand cmd; string cmdString = "Select CompanyName from Customers"; conn = new SqlConnection(@"Data Source=. \ SQLEXPRESS;AttachDbFilename= |DataDirectory| \ NORTHWND.MDF;Integrated Security=True; User Instance=True"); // Put this string on one line in your code cmd = new SqlCommand(cmdString, conn); conn.Open(); SqlDataReader myReader; List < string > returnData = new List < string > (); myReader = cmd.ExecuteReader(CommandBehavior.CloseConnection); while (myReader.Read()) { returnData.Add(myReader["CompanyName"].ToString()); Continued 379 Evjen c08.tex V2 - 01/28/2008 2:05pm Page 380 Chapter 8: Data Management with ADO.NET } return returnData; } } In this example, you create an instance of both the SqlConnection and the SqlCommand classes. Then, before you open the connection, you simply pass the SqlCommand class a SQL command selecting specific data from the Northwind database. After your connection is opened (based upon the commands passed in), you create a DataReader . To read the data from the database, you iterate through the data with the DataReader by using the myReader.Read() method. After the List(Of String) object is built, the connection is closed, and the object is returned from the function. Inserting Data When working with data, you often insert the data into the data source. Listing 8-2 shows you how to do this. This data may have been passed to you by the end user through the XML Web Service, or it may be data that you generated within the logic of your class. Listing 8-2: Inserting data into SQL Server VB Public Sub InsertData() Dim conn As SqlConnection Dim cmd As SqlCommand Dim cmdString As String = "Insert Customers (CustomerID, _ CompanyName, ContactName) Values (’BILLE’, ’XYZ Company’, ’Bill Evjen’)" conn = New SqlConnection("Data Source=. \ SQLEXPRESS;AttachDbFilename= |DataDirectory| \ NORTHWND.MDF;Integrated Security=True; User Instance=True") ’ Put this string on one line in your code cmd = New SqlCommand(cmdString, conn) conn.Open() cmd.ExecuteNonQuery() conn.Close() End Sub C# public void InsertData() { SqlConnection conn; SqlCommand cmd; string cmdString = "Insert Customers (CustomerID, CompanyName, ContactName) Values (’BILLE’, ’XYZ Company’, ’Bill Evjen’)"; conn = new SqlConnection(@"Data Source=. \ SQLEXPRESS;AttachDbFilename= |DataDirectory| \ NORTHWND.MDF;Integrated Security=True; User Instance=True"); // Put this string on one line in your code cmd = new SqlCommand(cmdString, conn); conn.Open(); cmd.ExecuteNonQuery(); conn.Close(); } 380 Evjen c08.tex V2 - 01/28/2008 2:05pm Page 381 Chapter 8: Data Management with ADO.NET Inserting data into SQL is pretty straightforward and simple. Using the SQL command string, you insert specific values for specific columns. The actual insertion is initiated using the cmd.Execute- NonQuery() command. This executes a command on the data when you don’t want anything in return. Updating Data In addition to inserting new records into a database, you frequently update existing rows of data in a table. Imagine a table in which you can update multiple records at once. In the example in Listing 8-3, you want to update an employee table by putting a particular value in the emp_bonus column if the employee has been at the company for five years or longer. Listing 8-3: Updating data in SQL Server VB Public Function UpdateEmployeeBonus() As Integer Dim conn As SqlConnection Dim cmd As SqlCommand Dim RecordsAffected as Integer Dim cmdString As String = "UPDATE Employees SET emp_bonus=1000 WHERE " & _ "yrs_duty > =5" conn = New SqlConnection("Data Source=. \ SQLEXPRESS;AttachDbFilename= |DataDirectory| \ NORTHWND.MDF;Integrated Security=True; User Instance=True") ’ Put this string on one line in your code cmd = New SqlCommand(cmdString, conn) conn.Open() RecordsAffected = cmd.ExecuteNonQuery() conn.Close() Return RecordsAffected End Function C# public int UpdateEmployeeBonus() { SqlConnection conn; SqlCommand cmd; int RecordsAffected; string cmdString = "UPDATE Employees SET emp_bonus=1000 WHERE yrs_duty > =5"; conn = new SqlConnection(@"Data Source=. \ SQLEXPRESS;AttachDbFilename= |DataDirectory| \ NORTHWND.MDF;Integrated Security=True; User Instance=True"); // Put this string on one line in your code cmd = new SqlCommand(cmdString, conn); conn.Open(); RecordsAffected = cmd.ExecuteNonQuery(); conn.Close(); return RecordsAffected; } 381 Evjen c08.tex V2 - 01/28/2008 2:05pm Page 382 Chapter 8: Data Management with ADO.NET This update function iterates through all the employees in the table and changes the value of the emp_bonus field to 1000 if an employee has been with the company for more than five years. This is done with the SQL command string. The great thing about these update capabilities is that you can capture the number of records that were updated by assigning the ExecuteNonQuery() command to the RecordsAffected variable. The total number of affected records is then returned by the function. Deleting Data Along with reading, inserting, a nd updating data, you sometimes need to delete data from the data source. Deleting data is a simple process of using the SQL command string and then the ExecuteNon- Query() command as you did in the update example. See Listing 8-4 for an illustration of this. Listing 8-4: Deleting data from SQL Server VB Public Function DeleteEmployee() As Integer Dim conn As SqlConnection Dim cmd As SqlCommand Dim RecordsAffected as Integer Dim cmdString As String = "DELETE Employees WHERE LastName=’Evjen’" conn = New SqlConnection("Data Source=. \ SQLEXPRESS;AttachDbFilename= |DataDirectory| \ NORTHWND.MDF;Integrated Security=True; User Instance=True") ’ Put this string on one line in your code cmd = New SqlCommand(cmdString, conn) conn.Open() RecordsAffected = cmd.ExecuteNonQuery() conn.Close() Return RecordsAffected End Function C# public int DeleteEmployee() { SqlConnection conn; SqlCommand cmd; int RecordsAffected; string cmdString = "DELETE Employees WHERE LastName=’Evjen’"; conn = new SqlConnection(@"Data Source=. \ SQLEXPRESS;AttachDbFilename= |DataDirectory| \ NORTHWND.MDF;Integrated Security=True; User Instance=True"); // Put this string on one line in your code cmd = new SqlCommand(cmdString, conn); conn.Open(); RecordsAffected = cmd.ExecuteNonQuery(); conn.Close(); return RecordsAffected; } You can assign the ExecuteNonQuery() command to an Integer variable (just as you did for the update function) to return the number of records deleted. 382 Evjen c08.tex V2 - 01/28/2008 2:05pm Page 383 Chapter 8: Data Management with ADO.NET Basic ADO.NET Namespaces and Classes The six core ADO.NET namespaces are shown in the following table. In addition to these namespaces, each new data provider can have its own namespace. As an example, the Oracle .NET data provider adds anamespaceof System.Data.OracleClient (for the Microsoft-built Oracle data provider). Namespace Description System.Data This namespace is the core of ADO.NET. It contains classes used by all data providers. It contains classes to represent tables, columns, rows, and the DataSet class. It also contains several useful interfaces, such as IDbCommand , IDbConnection ,and IDbDataAdapter . These interfaces are used by all managed providers, enabling them to plug into the core of ADO.NET. System.Data.Common This namespace defines common classes that are used as base classes for data providers. All data providers share these classes. A few examples are DbConnection and DbDataAdapter . System.Data.OleDb This namespace defines classes that work with OLE-DB data sources using the .NET OleDb data provider. It contains classes such as OleDbConnection and OleDbCommand . System.Data.Odbc This namespace defines classes that work with the ODBC data sources using the .NET ODBC data provider. It contains classes such as OdbcConnection and OdbcCommand . System.Data.SqlClient This namespace defines a data provider for the SQL Server 7.0 or higher database. It contains classes such as SqlConnection and SqlCommand . System.Data.SqlTypes This namespace defines a few classes that represent specific data types for the SQL Server database. ADO.NET has three distinct types of classes commonly referred to as Disconnected , Shared ,and Data Providers .The Disconnected classes provide the basic structure for the ADO.NET framework. A good exampleofthistypeofclassisthe DataTable class. The objects of this class are capable of storing data without any dependency on a specific data provider. The Shared classes form the base classes for data providers and are shared among all data providers. The Data Provider classes are meant to work with different kinds of data sources. They are used to perform all data-management operations on specific databases. The SqlClient data provider, for example, works only with the SQL Server database. A data provider contains Connection , Command , DataAdapter ,and DataReader objects. Typically, in programming ADO.NET, you first create the Connection object and provide it with the necessary information, such a s the connection string. You t hen create a Command object and provide it with the details of the SQL command that is to be executed. This command can be an inline SQL text command, a stored procedure, or direct table access. You can also provide parameters to these commands if needed. After you create the Connection and the Command objects, you must decide whether the command returns a result set. If the command doesn’t return a result set, you can simply execute the command by calling one of its several Execute methods. On the other hand, if the command returns a result set, you must make a decision about whether you want to retain the result set for future uses without maintain- ing the connection to the database. If you want to retain the result set, you must create a DataAdapter 383 Evjen c08.tex V2 - 01/28/2008 2:05pm Page 384 Chapter 8: Data Management with ADO.NET object and use it to fill a DataSet or a DataTable object. These objects are capable of maintaining their information in a disconnected mode. However, if you don’t want t o retain the result set, but rather to simply process the command in a swift fashion, you can use the Command object to create a DataReader object. The DataReader object needs a live connection to the database, and it works as a forward-only, read-only cursor. Using the Connection Object The Connection object creates a link (or connection) to a specified data source. This object must contain the necessary information to discover the specified data source and to log in to it properly using a defined username and password combination. This information is provided via a single string called a connection string. You can also store this connection string in the web.config file of your application. Every type of data provider has a connection object of some kind. The data provider for working with a SQL data store includes a SqlConnection class that performs this type of operation. T he SqlConnection object is a class that is specific to the SqlClient provider. As discussed earlier in this chapter, the SqlClient provider is built for working with the SQL Server 7.0 and higher databases. The properties for the SqlConnection class are shown in the following table. Property Description ConnectionString This property allows you to read or provide the connection string that should be used by the SqlConnection object. Database This read-only property returns the name of the database to use after the connection is opened. Datasource This read-only property returns the name of the instance of the SQL Server database used by the SqlConnection object. State This read-only property returns the current state of the connection. The possible values are Broken , Closed , Connecting , Executing , Fetching ,and Open . Connecting to a data source is probably the most common task when you are working with data. This example and the ones that follow assume that you have a SQL Server database. In order to connect to your SQL Server database, you use the SqlConnection class. This is shown in Listing 8-5. Listing 8-5: Connecting to a SQL database VB Dim conn as SqlConnection conn = New SqlConnection("Data Source=. \ SQLEXPRESS;AttachDbFilename= |DataDirectory| \ NORTHWND.MDF;Integrated Security=True; User Instance=True") ’ Put this string on one line in your code conn.Open() C# SqlConnection conn; conn = new SqlConnection(@"Data Source=. \ SQLEXPRESS;AttachDbFilename= 384 Evjen c08.tex V2 - 01/28/2008 2:05pm Page 385 Chapter 8: Data Management with ADO.NET |DataDirectory| \ NORTHWND.MDF;Integrated Security=True; User Instance=True"); // Put this string on one line in your code conn.Open(); To make this connection work, be sure that the proper namespaces are imported before you start using any of the classes that work with SQL. The first step in making a connection is to create an instance of the SqlConnection class and assign it to the conn instance. This SqlConnection class is initialized after you pass in the connection string as a parameter to the class. In this case, you are connecting to the Northwind database that resides on your local machine using the system administrator’s login credentials. Another means of making a connection is to put the connection string within the application’s web.config file and then to make a reference to the web.config file. With ASP.NET 3.5, you will find that there is an easy way to manage the storage of your connection strings through the use of the web.config file. This is actually a better way to store your connection strings rather than hard-coding them within the code of the application itself. In addition to having a single point in the application where the credentials for database access can be managed, storing credentials in the web.config also gives you the ability to encrypt the credentials. To define your connection string within the web.config file, you are going t o make use of the < connectionStrings > section. From this section, you can place an < add > element within it to define your connection. An example of this is illustrated in Listing 8-6. Listing 8-6: Providing your connection string within the web.config file < connectionStrings > < add name="DSN_Northwind" connectionString="Data Source=. \ SQLEXPRESS;AttachDbFilename=|DataDirectory| \ NORTHWND.MDF;Integrated Security=True;User Instance=True" providerName="System.Data.SqlClient" / > < /connectionStrings > In many places of this chapter, you will see that the actual connection string i s broken up on multiple lines. This connection string will need to be on a single line within your code or broken up with string concatenation. Now t hat you have a connection string within the web.config file, you can then make use of that connection string directly in your code by using the ConnectionManager object as illustrated here in Listing 8-7. Listing 8-7: Using the connection string found in the web.config file VB conn = New _ SqlConnection( _ ConfigurationManager.ConnectionStrings("DSN_Northwind").ConnectionString) C# conn = new SqlConnection( ConfigurationManager.ConnectionStrings["DSN_Northwind"].ConnectionString); 385 . 01/28/2008 2:01pm Page 37 5 Chapter 7: Data Binding in ASP. NET 3. 5 Summary In this chapter, you examined data binding in ASP. NET. The introduction of data source controls such as the LinqDataSource control,. a minimal amount of coding. You saw how ASP. NET includes a multitude of controls that can be data-bound, specifically examining how, since ASP. NET 1.0/1.1, many controls have been enhanced, and. at how the inline data-binding syntax has been improved and strengthened with the addition of the XML-specific data-binding expressions. 37 5 Evjen c08.tex V2 - 01/28/2008 2:05pm Page 37 7 Data Management with