Microsoft Visual C++ .NET Professional Projects - Premier Press
.pdf
INTRODUCTION TO ADO.NET |
Chapter 13 |
461 |
|
|
|
|
|
untyped dataset by exporting the structure to a schema file by using the
WriteXmlSchema() method.
An interesting aspect of untyped datasets is that the components of the dataset are available as collections. Therefore, in an untyped dataset, there exist collections, such as collections of DataTable objects and DataColumn objects. This also means that to access a specific dataset component, you need to iterate through the collection of the dataset component or refer to an item by name or index. You can access the collection of DataTable and DataColumn objects in an untyped dataset by using the Tables and Columns properties of the dataset, respectively.
I will now discuss the other component of ADO.NET, the .NET data provider.
.NET Data Providers
As discussed earlier, a .NET data provider is used to establish a connection with the data source, execute commands, and retrieve results. After you work with the results (data) retrieved from the data source, the .NET data provider is again used to update the changes in the data source. Thus, the .NET data provider acts as a bridge between the application and the data source.
A .NET data provider consists of the following four core components:
The Connection object: To transfer data between an application and the database, you first need to connect to the database. ADO.NET provides the Connection object that enables you to establish and manage a connection with the database. The ADO.NET Connection object is similar to the ADO Connection object.
The Command object: After establishing a connection with the database, you can use the Command object for processing requests (in the form of commands) and returning results of these requests from the database. The Command object enables you to perform operations such as updating the records of the database. This object is used when there is a connection with the database. The Command object is quite similar to the ADO
Command object but some new functions have been added to the
ADO.NET Command object.
The DataReader object: The DataReader object is used for reading data in a sequential manner. This object is similar to a read-only, forwardonly recordset and is used for retrieving read-only, forward-only data stream from the database. The DataReader object allows only one row of
462 Project 3 ADO.NET IN MANAGED C++
data to be stored in the memory at any point of time. This results in more efficient performance of the application and reduction in the system overheads.
The DataAdapter object: The DataAdapter object is used for transferring data from the data source to the dataset and vice versa. You work with data in the dataset and then transfer the changed data back to the data source.
So, the DataAdapter object is used for communication between the data source and the dataset. The DataAdapter object can transfer data not only between a dataset and a database but also between a dataset and some other sources, such as the Microsoft Exchange Server.
The DataAdapter class consists of a set of properties that facilitate loading and updating data. Table 13-2 lists some DataAdapter properties.
Table 13-2 DataAdapter Properties
Property |
Description |
SelectCommand |
Returns or sets a T-SQL statement or stored procedure used to |
|
select records from a data source. |
UpdateCommand |
Returns or sets a T-SQL statement or stored procedure used to |
|
update records in a data source. |
DeleteCommand |
Returns or sets a T-SQL statement or stored procedure used to |
|
delete records from a dataset. |
InsertCommand |
Returns or sets a T-SQL statement or stored procedure used to |
|
insert records in a data source. |
|
|
Figure 13-4 illustrates the interaction between the .NET data provider objects.
After having discussed the various core components of a .NET data provider, you will now revisit the types of .NET data providers.
ADO.NET provides the following types of .NET data providers:
The OLE DB .NET data provider
The SQL Server .NET Data Provider
ODBC .NET data provider
You use the ODBC .NET data provider to access ODBC-compliant data sources. The following sections discuss the first two .NET data providers in detail. The
INTRODUCTION TO ADO.NET |
Chapter 13 |
463 |
|
|
|
|
|
Connection object
Database
CommandObject
DataReaderObject
DataAdapterObject
FIGURE 13-4 Interaction between the .NET data provider objects
implementation of the ODBC .NET data provider is similar to the other two
.NET data providers.
In addition to the .NET data providers provided by ADO.NET, you can create and implement your own .NET data providers. Figure 13-5 illustrates the different components and types of .NET data providers.
The OLE DB .NET Data Provider
The OLE DB .NET data provider enables you to access data by using COM interoperability. It works with several OLE DB providers, such as SQLOLEDB (the SQL OLE DB provider), MSDAORA (the Oracle OLE DB provider), and Microsoft.Jet.OLEDB.4.0 (the Jet OLE DB provider). However, it does not provide support for MSDASQL, the OLE DB provider for ODBC.
As discussed earlier, the classes of the OLE DB .NET data provider are stored in the System.Data.OleDb namespace. Some of the most common classes for the OLE DB .NET data provider are described in Table 13-3.
464 Project 3 ADO.NET IN MANAGED C++
.NET data providers
|
|
|
|
|
|
|
|
|
|
Objects |
|
|
|
|
Types |
||||
|
|
|
|
|
|
|
|
|
|
|
|
|
Connection |
|
|
SQL server |
|
||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Command |
|
|
|
|
|
|
|
|
|
|
|
|
OLE DB |
|
||
|
|
|
|
||||||
|
|
|
DataReader |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
DataAdapter |
|
|
ODBC |
|
|
|
|
|
|
|
|
|
|
|
|
|
FIGURE 13-5 Components and types of .NET data providers
Table 13-3 Classes for OLE DB .NET Data Provider
Class |
Description |
OleDbConnection |
Represents an open connection with the data source. |
OleDbCommand |
Represents a SQL statement or stored procedure for execution |
|
against the data source. |
OleDbDataReader |
Provides a means to read data rows from the data source in a for- |
|
ward-only mode. Has similarity to the read-only, forward-only |
|
recordset of ADO. |
OleDbDataAdapter |
Represents the data commands and database connections used for |
|
transfer of data from the data source to the dataset and vice versa. |
OleDbError |
Compiles information pertaining to errors or warnings that the |
|
data source returns. |
|
INTRODUCTION TO ADO.NET |
Chapter 13 |
465 |
||
|
|
|
|
|
|
|
|
|
|
|
|
Class |
Description |
|
|
|
|
|
|
|
|
|
|
OleDbException |
Represents the exception that results when the OLE DB data |
||||
|
source returns an error or warning. |
|
|
|
|
OleDbPermission |
Enables the OLE DB .NET data provider to verify whether a |
||||
|
user has enough security permissions to acquire access to the |
||||
|
OLE DB data source. |
|
|
|
|
OleDbTransaction |
Represents a SQL transaction for the data source. |
|
|
|
|
|
|
|
|
|
|
The SQL Server .NET Data Provider
The SQL Server .NET data provider enables access specifically to Microsoft SQL Server databases by using the Tabular Data System (TDS) protocol. For this purpose, the SQL Server .NET data provider does not require the use of any OLE DB provider through COM interoperability. To be able to use the SQL Server .NET data provider, you need to have access to Microsoft SQL Server 7.0 or later.
As discussed earlier, the classes of the SQL Server .NET data provider are stored in the System.Data.SqlClient namespace. Some of the most commonly used classes for SQL Server .NET data provider are described in Table 13-4.
Table 13-4 Classes for SQL Server .NET Data Provider
Class |
Description |
SqlConnection |
Represents an open connection with a SQL Server database. |
SqlCommand |
Represents a Transact-SQL statement or stored procedure for |
|
execution against the Microsoft SQL Server database. |
SqlDataReader |
Provides a means to read data rows from the Microsoft SQL |
|
Server database in a forward-only mode. |
SqlDataAdapter |
Represents the data commands used for transfer of data from the |
|
Microsoft SQL Server database to the dataset and vice versa. |
SqlError |
Compiles information pertaining to errors or warnings that the |
|
Microsoft SQL Server database returns. |
SqlException |
Represents the exception that results when the Microsoft SQL |
|
Server returns an error or warning. |
SqlTransaction |
Represents a Transact-SQL transaction for the Microsoft SQL |
|
Server database. |
|
|
466 Project 3 ADO.NET IN MANAGED C++
Table 13-5, 13-6, 13-7, and 13-8 describe the methods of the classes SqlConnec-
tion, SqlCommand, SqlDataReader, and SqlDataAdapter, respectively.
Table 13-5 SqlConnection Methods
Method Description
ChangeDatabase |
Changes the current database to use another database for an exist- |
|
ing SqlConnection. |
Close |
Closes the connection with a database. |
CreateCommand |
Creates and returns an SqlCommand object for a particular |
|
SqlConnection. |
|
|
Table 13-6 SqlCommand Methods |
|
|
|
Method |
Description |
|
|
ExecuteReader |
Returns a DataReader object by invoking commands by using |
|
the T-SQL sp_executesql system stored procedure. |
ExecuteNonQuery |
Executes commands that do not return rows, such as T-SQL |
|
INSERT, DELETE, UPDATE, and SET statements. |
ExecuteScalar |
Retrieves the value of the first column of the first row in the |
|
result set obtained after executing a query. |
|
|
Table 13-7 SqlDataReader Methods |
|
|
|
Method |
Description |
|
|
Read |
Accesses the current row of the result set retrieved from a data |
|
source and moves SqlDataReader forward to the next row. |
NextResult |
Navigates through result sets in a sequential manner. Applicable |
|
only when DataReader consists of multiple result sets. |
GetSchemaTable |
Retrieves the schema-related information about the current result |
|
set in the form of a DataTable object. |
GetDateTime |
Returns the column value as a DateTime object. |
GetInt32 |
Returns the column value as a 32-bit signed integer. |
Close |
Closes the current DataReader object. |
|
|
|
INTRODUCTION TO ADO.NET |
Chapter 13 |
467 |
||
Table 13-8 SqlDataAdapter Methods |
|
|
|
|
|
|
|
|
|
||
|
|
|
|
|
|
Method |
Description |
|
|
|
|
|
|
|
|
|
|
Fill |
Populates or refreshes data in a dataset and uses the same data |
||||
|
structure in the dataset as in the data source. |
|
|
|
|
Update |
Modifies a data source to reflect changes in the data of a dataset |
||||
|
by using the appropriate T-SQL statements, such as INSERT, |
||||
|
UPDATE, or DELETE statements, against the data source. |
||||
|
|
|
|
|
|
After having discussed the types of .NET data providers, you might be wondering how to decide the type of data provider for your application. The .NET data provider you need to use is determined by the nature of the application and the data source that is to be accessed. The recommended implementations for .NET data providers are as follows:
SQL Server .NET data provider: This data provider is recommended in case of middle-tier applications using SQL Server 7.0 or later and sin- gle-tier applications using Microsoft Data engine (MSDE) or SQL Server 7.0 or later.
OLE DB .NET data provider: This data provider is recommended in case of middle-tier applications using Oracle or SQL Server 6.5 or earlier and single-tier applications using the MS Access database.
ADO.NET and XML
An important feature of ADO.NET is its built-in support for XML. ADO.NET was designed along with the .NET XML Framework. Both of them are components of the same architecture. ADO.NET provides both implicit and explicit support for XML, as compared to ADO, which does not inherently support XML but provides only an explicit XML support. ADO.NET uses XML internally as the format for storing and transferring data. This is a major advantage over ADO. You need not know XML to work with ADO.NET. This is because you are not exposed to the process of converting data into and from XML.
To understand the reason for choosing XML with ADO.NET, you need to know the advantages of using XML. An important advantage of XML is that it is an industry standard format. XML facilitates data exchange between components of one application with any other data component of another application. In
468 Project 3 ADO.NET IN MANAGED C++
addition, XML is a text-based format. This implies that XML can be sent through any protocol, such as HTTP. The exclusion of any binary information in XML also facilitates easy communication across networks by bypassing firewalls.
Extensive support for XML was built in ADO.NET keeping the advantages of XML in mind. For instance, the two-way exchange of data between a dataset and a data source is performed using XML. Similarly, data exchange between the components of the ADO.NET architecture occurs through XML. To facilitate data exchange between the components of the ADO.NET architecture, the contents of DataSet are converted to XML files or streams by data APIs. This XML format is then sent to another component where data APIs can be used to convert the XML format to a DataSet object. In addition, you can populate a dataset with data from an XML source, such as an XML file or an XML stream of data.
Summary
In this chapter, you were first introduced to the various data access techniques: DAO, ODBC, RDO, OLE DB, and ADO. You also learned about the advantages and disadvantages of these techniques and about their evolution. Next, you were introduced to ADO.NET and its features and advantages. You learned that ADO.NET supports disconnected data architecture, provides datasets, and supports XML. ADO.NET makes applications scalable by enabling them to effectively manage multiple users. ADO.NET applications also provide better performance and are easily programmable. ADO.NET enables you to create applications that are interoperable with other applications as well as easy to maintain.
Next, you were introduced to ADO.NET architecture. You first learned about data-related namespaces and then about the two main components of ADO.NET, datasets and .NET data providers. You learned about the two types of .NET data providers, the OLE DB .NET data provider and the SQL Server
.NET data provider. Finally, you learned about the ADO.NET support for XML. ADO.NET provides implicit as well as explicit support for XML. XML is integrated with ADO.NET in the form of the DataSet.
In the next chapter, you will learn to implement ADO.NET in a Managed Extensions application.
Chapter 14
Implementing
ADO.NET in a
Managed C++
Application