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 classe

[ 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

_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

n

DataTable

methods

NewTableNameRowAddTableNameRowDeleteTableNa

DataRowCollect

DataColumn DataTable.ColumnNameColumnDataRow.ColumnName typedName

en

Parent accessor TableNameRow typedParent

DataSet events TableNameRowChangeEventTableNameRowChangeEv

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

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