Tài liệu Controlling the Names Used in a Strongly Typed DataSet pdf

[ Team LiB ] Recipe 2.18 Controlling the Names Used in a Strongly Typed DataSet Problem You want to assign your own names to the classes and properties for strongly typed DataSet classes. Solution Use annotations in the XML schema to control the names of classes and properties in strongly typed DataSet classes. The sample uses one XSD file: CategoriesDS_AnnotatedName.xsd The schema used to generate the strongly typed DataSet. The schema is annotated so that you can access the collection of rows in the table by using the Categorys property of the DataSet rather than categories, each row by using the Category property of the row collection rather than CategoriesRow, and the CategoryName field by using the Name property of the row rather than CategoryName. The annotations are marked in bold in the Example 2-23 . Example 2-23. File: TypedDataSets\CategoriesDS_AnnotatedName.xsd <?xml version="1.0" standalone="yes" ?> <xs:schema id="CategoriesDS_AnnotatedName" targetNamespace= "http://www.tempuri.org/CategoriesDS_AnnotatedName.xsd" xmlns:mstns="http://www.tempuri.org/CategoriesDS_AnnotatedName.xsd" xmlns="http://www.tempuri.org/CategoriesDS_AnnotatedName.xsd" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:msdata="urn:schemas-microsoft-com:xml-msdata" xmlns:codegen="urn:schemas-microsoft-com:xml-msprop" attributeFormDefault="qualified" elementFormDefault="qualified"> <xs:element name="CategoriesDS_AnnotatedName" msdata:IsDataSet="true"> <xs:complexType> <xs:choice maxOccurs="unbounded"> <xs:element name="Categories" codegen:typedName="Category" codegen:typedPlural="Categorys"> <xs:complexType> <xs:sequence> <xs:element name="CategoryID" msdata:ReadOnly="true" msdata:AutoIncrement="true" type="xs:int" /> <xs:element name="CategoryName" type="xs:string" codegen:typedName="Name" /> <xs:element name="Description" type="xs:string" minOccurs="0" /> </xs:sequence> </xs:complexType> </xs:element> </xs:choice> </xs:complexType> <xs:unique name="Constraint1" msdata:PrimaryKey="true"> <xs:selector xpath=".//mstns:Categories" /> <xs:field xpath="mstns:CategoryID" /> </xs:unique> </xs:element> </xs:schema> The sample code creates a strongly typed DataSet based on the Categories table in Northwind. The user specifies whether the one based on the default or annotated schema file is used. In either case, data is loaded into the DataSet and the collections of rows and columns in the DataSet are iterated over to display the data and to demonstrate the effect of the schema annotations. The C# code is shown in Example 2-24 . Example 2-24. File: TypedDataSetNamesForm.cs // Namespaces, variables, and constants using System; using System.Configuration; using System.Text; using System.Data; using System.Data.SqlClient; // Table name constants private const String CATEGORIES_TABLE = "Categories"; // . . . StringBuilder result = new StringBuilder( ); // Create the DataAdapter. SqlDataAdapter da = new SqlDataAdapter("SELECT * FROM Categories", ConfigurationSettings.AppSettings["Sql_ConnectString"]); if (annotatedRadioButton.Checked) { // Create the typed DataSet with name annotations. CategoriesDS_AnnotatedName ds = new CategoriesDS_AnnotatedName( ); // Fill the Categories table within DataSet. da.Fill(ds, CATEGORIES_TABLE); result.Append("Annotated Names" + Environment.NewLine + Environment.NewLine); // Iterate over the rows collection and display columns. // Note that the row collection is Categorys // and that each row is Category. foreach(CategoriesDS_AnnotatedName.Category row in ds.Categorys) { // Note that the CategoryName field is referred to simply as Name. result.Append(row.CategoryID + "\t" + row.Name + "\t" + row.Description + Environment.NewLine); } } else { // Create the typed DataSet without name annotations. CategoriesDS ds = new CategoriesDS( ); da.Fill(ds, CATEGORIES_TABLE); result.Append("Default" + Environment.NewLine + Environment.NewLine); // Iterate over the rows collection and display columns. foreach(CategoriesDS.CategoriesRow row in ds.Categories) { result.Append(row.CategoryID + "\t" + row.CategoryName + "\t" + row.Description + Environment.NewLine); } } resultTextBox.Text = result.ToString( ); Discussion Annotations are modifications to the XSD schema used to generate a strongly typed DataSet that allows the names of elements in the strongly typed DataSet to be customized without changing the underlying schema. This allows more meaningful element names to be used resulting in code that is easier to read, use, and maintain. Table 2-16 lists available annotations. Table 2-16. Available annotations Annotation Description typedChildren Name of the method that returns objects from a child data relation. typedName Name of the object. typedParent Name of the method that returns an object from a parent data relation. typedPlural Name of the collection of objects. nullValue Value or behavior if the underlying value is DBNull. Table 2-17 lists possible values for this annotation. The default value is _throw. Table 2-17 describes possible values for the nullValue annotation. Table 2-17. Values for nullValue annotation nullValue Description Replacement Value A value having the same type as the element to be returned _empty Return String.Empty for a StringReturn an object created from an empty constructor for other objectsThrow an exception for primitive types _null Return a null reference for objectsThrow an exception for primitive types _throw Raise an exception Table 2-18 lists the different objects in a strongly typed DataSet and the default names and available annotations for each. Table 2-18. Default values and available annotations for elements of strongly typed DataSet objects Element Default name Annotatio n DataTable TableNameDataTable typedPlural DataTable methods NewTableNameRowAddTableNameRowDeleteTableNa meRow typedName DataRowCollect ion TableName typedPlural DataRow TableNameRow typedName DataColumn DataTable.ColumnNameColumnDataRow.ColumnName typedName Property PropertyName typedName Child accessor GetChildTableNameRows typedChildr en Parent accessor TableNameRow typedParent DataSet events TableNameRowChangeEventTableNameRowChangeEv entHandler typedName The use annotations, a reference to the codegen namespace, must be included in the XSD schema, as shown: xmlns:codegen="urn:schemas-microsoft-com:xml-msprop" The codegen namespace allows the names of methods, properties, relations, constraints, and events in the strongly typed DataSet to be customized. [ Team LiB ] . Default name Annotatio n DataTable TableNameDataTable typedPlural DataTable methods NewTableNameRowAddTableNameRowDeleteTableNa meRow typedName DataRowCollect. ion TableName typedPlural DataRow TableNameRow typedName DataColumn DataTable.ColumnNameColumnDataRow.ColumnName typedName Property PropertyName typedName