Professional ASP.NET 3.5 in C# and Visual Basic Part 36 ppsx

Evjen c07.tex V2 - 01/28/2008 2:01pm Page 305 Chapter 7: Data Binding in ASP.NET 3.5 < asp:querystringparameter DefaultValue="0" Name="CustomerID" QueryStringField="cid" Type="String" / > < /whereparameters > < /asp:LinqDataSource > You can add multiple Where parameters that the control will automatically concatenate in its Where property using the AND operator. You can manually change the default value of the Where property if you want to have multiple WhereParameters defined, but only use a subset, or if you want to change which parameters are used dynamically at runtime. This is shown in Listing 7-12, where the LinqDataSource control has several Where parameters defined, but by default is using only one. Listing 7-12: Using one of multiple defined WhereParameters < asp:LinqDataSource ID="LinqDataSource1" runat="server" ContextTypeName="NorthwindDataContext" TableName="Customers" Select="new (CustomerID, ContactName, ContactTitle, Region)" Where="Country == @Country" OrderBy="Region, ContactTitle, ContactName" > < whereparameters > < asp:querystringparameter DefaultValue="0" Name="CustomerID" QueryStringField="cid" Type="String" / > < asp:querystringparameter DefaultValue="USA" Name="Country" QueryStringField="country" Type="String" / > < asp:FormParameter DefaultValue="AZ" Name="Region" FormField="region" Type="String" / > < /whereparameters > < /asp:LinqDataSource > In this case, although three WhereParameters are defined, the Where property uses only the Country parameter. It would be simple to change the Where property’s value at runtime to use any of the defined parameters, based perhaps on a configuration setting set by the end user. The LinqDataSource control also includes a property called AutoGenerateWhereClause , which can sim- plify the markup created by the control. When set to True , the property causes the control to ignore the value of the Where property and automatically use each parameter specified in the Where parameters collection in the query’s Where clause. Defining an OrderBy Clause When defining an OrderBy clause, by default the wizard simply creates a comma-delimited list of fields as the value for the control’s OrderBy property. The value of the OrderBy property is then appended to the control’s LINQ query when it is executed. The control also exposes an OrderByParameters collection, which you can also use to specify OrderBy values. However, in most cases using the simple OrderBy property will be sufficient. You would need to the use OrderBy parameters collection only if you need to determine the value of a variable at runtime, and then order the query results based on that value. Grouping Query Data The LinqDataSource control also makes it easy to specify a grouping for the resultset returned by the query. In the configuration wizard, you can select the Group By field for the query. Once a field is selected, the wizard then creates a default projection based on the groupby field. The projection includes 305 Evjen c07.tex V2 - 01/28/2008 2:01pm Page 306 Chapter 7: Data Binding in ASP.NET 3.5 two fields by default, the first called key , which represents the group objects specified in the GroupBy property, and the second called it which represents the grouped objects. Y ou can also add your own columns to the projection and execute functions against the grouped data such as Average , Min , Max ,and Count . Listing 7-13 demonstrates a very simple grouping using the LinqDataSource control. Listing 7-13: Simple Data Grouping < asp:LinqDataSource ID="LinqDataSource1" runat="server" ContextTypeName="NorthwindDataContext" TableName="Products" Select="new (key as Category, it as Products, Average(UnitPrice) as Average_UnitPrice)" GroupBy="Category" > < /asp:LinqDataSource > You can see in this sample that the Products table has been grouped by its Category property. The LinqDataSource control created a new projection containing the key (aliased as Category )and it (aliased as Products ) fields. Additionally, the custom field average_unitprice has been added, which calculates the average unit price of the products in each category. When you execute this query and bind the results to a GridView, a simple view of the calculated average unit price is displayed. The Category and Products are not displayed because they are complex object types, and the GridView is not capable of directly displaying them. You can access the data in either key by using the standard ASP.NET Eval() function. In a GridView you would do this by creating a TemplateField ,andusing ItemTemplate to insert the Eval statement as shown here: < asp:TemplateField > < ItemTemplate > < %# Eval("Category.CategoryName") % > < /ItemTemplate > < /asp:TemplateField > In this case, TemplateField displays the CategoryName for each grouped category in the resultset. Accessing the grouped items is just as easy. If, for example, you wanted to include a bullet list of each product in an individual group, you would simply add another TemplateField , insert a BulletList control and bind it to the Products field returned by the query, as shown next: < asp:TemplateField > < ItemTemplate > < asp:BulletedList DataSource=’ < %# Eval("Products") % > ’ DataTextField="ProductName" runat="server" ID="BulletedList" / > < /ItemTemplate > < /asp:TemplateField > Data Concurrency Like the SqlDataSource control, the LinqDataSource control allows for data concurrency checks when updating or deleting data. As its name implies, the StoreOriginalValuesInViewState property indi- cates whether the data source control should store the original data values in ViewState. Doing this when using LINQ to SQL as the underlying data object, allows LINQ to SQL to perform data concurrency checking before submitting updates, or deleting data. 306 Evjen c07.tex V2 - 01/28/2008 2:01pm Page 307 Chapter 7: Data Binding in ASP.NET 3.5 Storing the original data in ViewState, however, can cause the size of your Web page to grow significantly, affecting the performance of your Web site, so you may wish to disable the storing of data in ViewState. If you do, recognize that you are now responsible for any data concurrency checking that your application requires. LinqDataSource Events The LinqDataSource control also includes a number of useful events that you can use to react to actions taken by the control at runtime. Standard before and after events for Select, Insert, Update, and Delete actions are all exposed and allow you to add, remove, or modify parameters from the control’s various parameter collections, or even cancel the event entirely. Additionally, the post action events allow you to determine whether an exception has occurred while attempting to execute an Insert, Update, or Delete. If an exception has occurred, these events allow you to react to those exceptions, and either mark the exception as handled, or allow it to continue to bubble up through the application. AccessDataSource Control Although you can use the SqlDataSource to connect to Access databases, ASP.NET also provides a special AccessDataSource control. This control gives you specialized access to Access databases using the Jet Data provider, but it still uses SQL commands to perform data retrieval because it is derived from the SqlDataSource. Despite its relative similarity to the SqlDataSource control, the AccessDataSource control has some specialized parts. First, the control does not require you to set a ConnectionString property. Instead, the control uses a DataFile property to allow you to directly specify the Access .mdb file you want to use for data access. A side effect of not having the ConnectionString property is that the AccessDataSource cannot connect to password-protected databases. If you need to access a password-protected Access database, you can use the SqlDataSource control, which allows you to provide the username and password as part of the connection string. Additionally, because the AccessDataSource uses the System.Data.OleDb to perform actual data access, the order of parameters matters. You need to verify that the order of the parameters in any Select, Insert, Update, or Delete parameters collection matches the order of the parameters in the SQL statement. XmlDataSource Control The XmlDataSource control provides you with a simple way of binding XML documents, either in- memory or located on a physical drive. The control provides you with a number of properties that make it easy to specify an XML file containing data and an XSLT transform file for converting the source XML into a more suitable format. You can also provide a n XPath query to select only a certain subset of data. You can use the XmlDataSource control’s Configure Data Wizard, shown in Figure 7-11, to configure the control. Listing 7-14 shows how you might consume an RSS feed from the MSDN Web site, selecting all the item nodes within it for binding to a bound list control such as the GridView. 307 Evjen c07.tex V2 - 01/28/2008 2:01pm Page 308 Chapter 7: Data Binding in ASP.NET 3.5 Figure 7-11 Listing 7-14: Using the XmlDataSource control to consume an RSS feed < asp:XmlDataSource ID="XmlDataSource1" Runat="server" DataFile="http://msdn.microsoft.com/rss.xml" XPath="rss/channel/item" < /asp:XmlDataSource > In addition to the declarative attributes you can use with the XmlDataSource, a number of other helpful properties and events are available. Many times, your XML is not stored in a physical file, but rather is simply a string stored in your appli- cation memory or possibly in a SQL database. The control provides the Data property, which accepts a simple string of XML to which the control can bind. Note that if both the Data and DataFile properties are set, the DataFile property takes precedence over the Data property. Additionally, in certain scenarios, you may w ant to e xport the bound XML out of the XmlDataSource control to other objects or e ven save any changes that have been made to the underlying XML if it has been bound to a control such as a GridView. The XmlDataSource control provides two methods to accommodate this. First, the GetXmlDocument method allows you to export the XML by returning a basic System.Xml.XmlDocument object that contains the XML loaded in the data source control. 308 Evjen c07.tex V2 - 01/28/2008 2:01pm Page 309 Chapter 7: Data Binding in ASP.NET 3.5 Second, using the control’s Save method, you can persist changes made to the XmlDataSource control’s loaded XML back to disk. Executing this method assumes you have provided a file path in the DataFile property. The XmlDataSource control also provides you with a number of specialized events. The Transforming event that is raised before the XSLT transform specified in the Transform or TransformFile properties is applied and allows you to supply custom arguments to the transform. ObjectDataSource Control The ObjectDataSource control is one of the most interesting data source controls in the ASP.NET tool- box. It gives you the power to bind data controls to middle-layer business objects that can be hard-coded or automatically generated from programs such as Object Relational (O/R) mappers. To demonstrate how to use the ObjectDataSource control, create a class in the project that represents a customer. Listing 7-15 shows a class that you can use for this demonstration. Listing 7-15: Creating a Customer class to demonstrate the ObjectDataSource control VB Public Class Customer Private _customerID As Integer Private _companyName As String Private _contactName As String Private _contactTitle As String Public Property CustomerID() As Integer Get Return _customerID End Get Set _customerID = value End Set End Property Public Property CompanyName() As Integer Get Return _companyName End Get Set _companyName = value End Set End Property Public Property ContactName() As Integer Get Return _contactName End Get Set _contactName = value End Set Continued 309 Evjen c07.tex V2 - 01/28/2008 2:01pm Page 310 Chapter 7: Data Binding in ASP.NET 3.5 End Property Public Property ContactTitle() As Integer Get Return _contactTitle End Get Set _contactTitle = value End Set End Property Public Function [Select](ByVal customerID As Integer) As System.Data.DataSet ’ You would implement logic here to retreive ’ Customer data based on the customerID parameter Dim ds As New System.Data.DataSet() ds.Tables.Add(New System.Data.DataTable()) Return ds End Function Public Sub Insert(ByVal c As Customer) ’ Implement Insert logic End Sub Public Sub Update(ByVal c As Customer) ’ Implement Update logic End Sub Public Sub Delete(ByVal c As Customer) ’ Implement Delete logic End Sub End Class C# public class Customer { private int _customerID; private string _companyName; private string _contactName; private string _contactTitle; public int CustomerID { get { return _customerID; } set { _customerID = value; } } Continued 310 Evjen c07.tex V2 - 01/28/2008 2:01pm Page 311 Chapter 7: Data Binding in ASP.NET 3.5 public string CompanyName { get { return _companyName; } set { _companyName = value; } } public string ContactName { get { return _contactName; } set { _contactName = value; } } public string ContactTitle { get { return _contactTitle; } set { _contactTitle = value; } } public Customer() { } public System.Data.DataSet Select(Int32 customerId) { // Implement logic here to retrieve the Customer // data based on the methods customerId parameter System.Data.DataSet ds = new System.Data.DataSet(); ds.Tables.Add(new System.Data.DataTable()); return ds; } Continued 311 Evjen c07.tex V2 - 01/28/2008 2:01pm Page 312 Chapter 7: Data Binding in ASP.NET 3.5 public void Insert(Customer c) { // Implement Insert logic } public void Update(Customer c) { // Implement Update logic } public void Delete(Customer c) { // Implement Delete logic } } To start using the ObjectDataSource, drag the control onto the designer surface. Using the control’s smart tag, load the Configuration Wizard by selecting the Configure Data Source option. After the wizard opens, it asks you to select the business object you want to use as your data source. The drop-down list shows all the classes located in the App_Code folder of your Web site that can be successfully compiled. In this case, you want to use the Customer class shown in Listing 7-8. Click the Next button, and the wizard asks you to specify which methods it should use for the CRUD operations it can perform: SELECT, INSERT, UPDATE, and DELETE. Each tab lets you select a specific method located in your business class to perform the specific action. Figure 7-12 shows that you want the control to use a method called Select() to retrieve data. The methods the ObjectDataSource uses to perform CRUD operations must follow certain rules in order for the control to understand. For instance, the control’s SELECT method must return a DataSet , DataReader , or a strongly typed collection. Each of the control’s operation tabs explains what the control expects of the method you specify for it to use. Additionally, if a method does not conform to the rules that specific operation expects, it is not listed in the drop-down list on that tab. Finally, if your SELECT method contains parameters, the wizard lets you create SelectParameters you can use to provide the method parameter data. When you have completed configuring the ObjectDataSource, you should have code in your page source like that shown in Listing 7-16. Listing 7-16: The ObjectDataSource code generated by the configuration wizard < asp:ObjectDataSource ID="ObjectDataSource1" runat="server" DeleteMethod="Delete" InsertMethod="Insert" SelectMethod="Select" TypeName="Customer" UpdateMethod="Update" > < SelectParameters > < asp:QueryStringParameter Name="customerID" QueryStringField="ID" Type="Int32" / > < /SelectParameters > < /asp:ObjectDataSource > As you can see, the wizard has generated the attributes for the SELECT , UPDATE , INSERT ,and DELETE methods you specified in the w izard. Also notice that it has added the Select parameter. Depending 312 Evjen c07.tex V2 - 01/28/2008 2:01pm Page 313 Chapter 7: Data Binding in ASP.NET 3.5 on your application, you could change this to any of the Parameter objects discussed earlier, such as a ControlParameter or QuerystringParameter object. Figure 7-12 ObjectDataSource Events The ObjectDataSource control exposes several useful events that you can hook into. First, it includes events that are raised before and after the control performs any of the CRUD actions, such as selecting or deleting events. It also includes pre- and post-events that are raised when the object that is serving a s the data source is created or disposed of, as well as when an event that is raised before a filter is applied to the data. All these events give you great power when you must react to the different ways the ObjectDataSource control behaves. 313 Evjen c07.tex V2 - 01/28/2008 2:01pm Page 314 Chapter 7: Data Binding in ASP.NET 3.5 SiteMapDataSource Control The SiteMapDataSource enables you to work with data stored in your Web site’s SiteMap configuration file if you have one. This can be useful if you are changing your site map data at runtime, perhaps based on user privilege or status. Note two items regarding the SiteMapDataSource control. First, it does not support any o f the data caching options that exist in the other data source controls provided (covered in the next section), so you cannot natively cache your sitemap data. Second, the SiteMapDataSource control does not have any configuration wizards like the other data source controls. This is because the SiteMap control can be bound only to the SiteMap configuration data file of your Web site, so no other configuration is possible. Listing 7-17 shows an example of using the SiteMap control. Listing 7-17: Using the SiteMapDataSource control < asp:SiteMapDataSource ID="SiteMapDataSource1" Runat="server" / > Using the SiteMapDataSource control is discussed in greater detail in Chapter 14. Configuring Data Source Control Caching Caching is built into all the data source controls that ship with ASP.NET except the SiteMapDataSource control. This means that you can easily configure and control data caching using the same declarative syn- tax. All data source controls (except the SiteMapDataSource control) enable you to create basic caching policies including a cache direction, expiration policies, and key dependencies. Remember that the SqlDataSource control’s caching features are available only if y ou have set the DataSourceMode property to DataSet . If it is set to DataReader , the control throws a NotSupport- edException . Cache duration can be set to a specific length of time, such as 3600 seconds (60 minutes), or you can set it to Infinite to force the cached data to never expire. Listing 7-18 shows how you can easily add caching features to a data source control. Listing 7-18: Enabling caching on a SqlDataSource control < asp:SqlDataSource ID="SqlDataSource1" Runat="server" SelectCommand="SELECT * FROM [Customers]" ConnectionString=" < %$ ConnectionStrings:AppConnectionString1 % > " DataSourceMode="DataSet" ConflictDetection="CompareAllValues" EnableCaching="True" CacheKeyDependency="SomeKey" CacheDuration="Infinite" > < SelectParameters > < asp:QueryStringParameter Name="CustomerID" QueryStringField="id" Type="String" >< /asp:QueryStringParameter > < /SelectParameters > < /asp:SqlDataSource > Some controls also extend this core set of caching features with additional caching functionality specific to their data sources. For instance, if you are using the SqlDataSource control, you can use the 314 . allows LINQ to SQL to perform data concurrency checking before submitting updates, or deleting data. 30 6 Evjen c07.tex V2 - 01/28/2008 2:01pm Page 30 7 Chapter 7: Data Binding in ASP. NET 3. 5 Storing. 2:01pm Page 30 5 Chapter 7: Data Binding in ASP. NET 3. 5 < asp: querystringparameter DefaultValue="0" Name="CustomerID" QueryStringField="cid" Type="String". returning a basic System.Xml.XmlDocument object that contains the XML loaded in the data source control. 30 8 Evjen c07.tex V2 - 01/28/2008 2:01pm Page 30 9 Chapter 7: Data Binding in ASP. NET 3. 5 Second,