Tài liệu Practical Database Programming With Visual C#.NET- P2 pdf

2.11 Create Oracle 10g XE Sample Database 81Figure 2.59 Create the foreign key between the LogIn and the Faculty table.. To create a foreign key from the LogIn table and connect it to t

2.11 Create Oracle 10g XE Sample Database 73

Figure 2.51 Completed LogIn table

length of the string depends on the number of real letters entered by the user The data types for all columns are VARCHAR2 with one exception, which is the phone column that has a CHAR type with an upper bound of 12 letters since our phone numbers are composed of 10 digits, and we can extend this length to 12 with two dashes For all other columns, the length varies with the different information, so the VARCHAR2 is selected for those columns

The fi nished design view of your Faculty table is shown in Figure 2.52 You need to check the Not Null checkbox for the faculty_id column since we selected this column as the primary key for this table

Click on the Next button to go to the next page to add the primary key for this table, which is shown in Figure 2.53

Check the Not Populated from the primary key list since we don ’ t want to use any Sequence object to automatically generate a sequence of numeric numbers as our primary key, and then select the FACULTY_ID(VARCHAR2) from the Primary Key textbox

In this way, the faculty_id column is selected as the primary key for this table Keep the Composite Primary Key box untouched since we do not have that kind of key in this table, and click on the Next button to go to the next page

Since we have not created all other tables to work as our reference tables for the foreign key, click on Next to continue, and we will do the foreign key for this table later

Click on the Finish button to go to the Confi rm page Finally click on the Create button

to create this new Faculty table Your completed columns in the Faculty table are shown

in Figure 2.54

Figure 2.52 Finished design view of the Faculty table

Figure 2.53 Opened Primary Key window

2.11 Create Oracle 10g XE Sample Database 75

Figure 2.54 Completed columns in the Faculty table

Table 2.24 Data in the Faculty Table

A52990 Black Anderson MTC-218 750-378-9987 Virginia Tech Professor banderson@college.edu A77587 Debby Angles MTC-320 750-330-2276 University of Chicago Associate Professor dangles@college.edu B66750 Alice Brown MTC-257 750-330-6650 University of Florida Assistant Professor abrown@college.edu B78880 Ying Bai MTC-211 750-378-1148 Florida Atlantic University Associate Professor ybai@college.edu B86590 Satish Bhalla MTC-214 750-378-1061 University of Notre Dame Associate Professor sbhalla@college.edu H99118 Jeff Henry MTC-336 750-330-8650 Ohio State University Associate Professor jhenry@college.edu J33486 Steve Johnson MTC-118 750-330-1116 Harvard University Distinguished Professor sjohnson@college.edu K69880 Jenney King MTC-324 750-378-1230 East Florida University Professor jking@college.edu

Now click on the Data object tool to add the data into this new table Click on the Insert Row button to add all rows that are shown in Table 2.24 into this table

Click on the Create and Create Another button when the fi rst row is done, and tinue to create all rows with the data shown in Table 2.24 You may click on the Create button for your last row Your fi nished Faculty table should match the one shown in Figure 2.55

2.11.2.3 Create Other Tables

In a similar way, you can continue to create the following three tables: Course, Student, and StudentCourse based on the data shown in Tables 2.25 , 2.26 , and 2.27

Figure 2.55 Finished Faculty table

The data types used in the Course table are:

• course_id: VARCHAR2(10) — primary Key

The data types used in the Student table are:

• student_id: VARCHAR2(10) — primary Key

The data types used in the StudentCourse table are:

• s_course_id: NUMBER(4, 0) — precision = 4, scale = 0 (4 - bit integer) primary key

• student_id: VARCHAR2(10)

2.11 Create Oracle 10g XE Sample Database 77 Table 2.25 Data in the Course Table

course_id course credit classroom schedule enrollment faculty_id

CSE-436 Automatic Control and Design 3 TC-305 M-W-F: 10:00-10:55 AM 29 J33486

CSE-438 Advd Logic & Microprocessor 3 TC-213 M-W-F: 11:00-11:55 AM 35 B78880

Table 2.26 Data in the Student Table

A97850 Ashly Jade 3.57 116 Information System Engineering Junior ajade@college.edu

2.11.3 Create Constraints Between Tables

Now it is the time for us to set up the relationships between our fi ve tables using the primary and foreign keys Since we have already selected the primary key for each table when we create and build those tables, therefore we only need to take care of the foreign keys and connect them with the associated primary keys in the related tables Let ’ s start from the fi rst table, LogIn table

Table 2.27 Data in the Student C ourse Table

2.11 Create Oracle 10g XE Sample Database 79

Figure 2.56 Completed Course table

Figure 2.57 Completed Student table

2.11.3.1 Create Constraints Between Log In and Faculty Tables

Now let ’ s create the constraints between the LogIn and the Faculty tables by using a foreign key Create a foreign key for the LogIn table and connect it to the primary key

in the Faculty table The faculty_id is a foreign key in the LogIn table but it is a primary key in the Faculty table A one - to - many relationship exists between the faculty_id in the Faculty table and the faculty_id in the LogIn table

Log on the Oracle Database 10g XE using the customer user name, CSE_DEPT, and the customer database password, and then open the home page of the Oracle Database 10g XE Click on the Object Browser icon and select Browse|Table to list all tables Select the LogIn table from the left pane to open it, click the Constraints tab and then click the Create button that is the fi rst button in the second row Enter LOGIN_FACULTY_FK into the Constraint Name box, and select the Foreign Key from the Constraint Type box, which is shown in Figure 2.59 Check the On Delete Cascade checkbox Then select the FACULTY_ID from the LogIn table as the foreign key column Select the FACULTY

Figure 2.58 Completed StudentCourse table

2.11 Create Oracle 10g XE Sample Database 81

Figure 2.59 Create the foreign key between the LogIn and the Faculty table

table from the Reference Table Name box as the reference table, and select the FACULTY_ID from the Reference Table Column List as the reference table column

Your fi nished Add Constraint window should match the one shown in Figure 2.59 Click on Next to go to the next window, and then click on the Finish button to confi rm this foreign key ’ s creation

2.11.3.2 Create Constraints Between Log In and Student Tables

The relationship between the Student table and the LogIn table is a one - to - many tionship The student_id in the Student table is a primary key, but the student_id in the LogIn table is a foreign key Multiple student_ids can exists in the LogIn table, but only one or a unique student_id can be found from the Student table

To create a foreign key from the LogIn table and connect it to the primary key in the Student table, open the LogIn table if it is not opened and click on the Constraints tab, and then click on the Create button that is the fi rst button in the second row to open the Add Constraint window Enter LOGIN_STUDENT_FK into the Constraint Name box, and select the Foreign Key from the Constraint Type box, which is shown in Figure 2.60 Check the On Delete Cascade checkbox Then select the STUDENT_ID from the LogIn table as the foreign key column Select the STUDENT table from the Reference Table Name box as the reference table, and select the STUDENT_ID from the Reference Table Column List as the reference table column Your fi nished Add Constraint window should match the one shown in Figure 2.60

Figure 2.61 Finished foreign key creation window for the LogIn table

Recall that when we created the LogIn table in Section 2.11.2.1 , we emphasized that for the blank fi elds in both faculty_id and student_id columns, don ’ t place a NULL into these fi elds and just leave those fi elds blank The reason for this is that an ALTER TABLE command will be issued when you create a foreign key for the LogIn table, and the NULL cannot be recognized by this command, therefore an error ORA - 02298 occurs and your creation of a foreign key will fail

Click on the Next button to go to the next window, and then click on the Finish button to confi rm this foreign key ’ s creation Your fi nished foreign key creation window for the LogIn table should match the one shown in Figure 2.61

Figure 2.60 Create the foreign key between the LogIn and the Student table

2.11 Create Oracle 10g XE Sample Database 83

2.11.3.3 Create Constraints Between Course and Faculty Tables

The relationship between the Faculty table and the Course table is a one - to - many tionship The faculty_id in the Faculty table is a primary key, but it is a foreign key in the Course table This means that only a unique faculty_id exists in the Faculty table but multiple faculty_ids can exist in the Course table since one faculty can teach multiple courses

Open the Course table by clicking it from the left panel Click on the Constraints tab and then click the Create button Enter COURSE_FACULTY_FK into the Constraint Name box, and select the Foreign Key from the Constraint Type box, which is shown in Figure 2.62 Check the On Delete Cascade checkbox Then select the FACULTY_ID from the Course table as the foreign key column Select the FACULTY table from the Reference Table Name box as the reference table, and select the FACULTY_ID from the Reference Table Column List as the reference table column Your fi nished Add Constraint window should match the one shown in Figure 2.62

Click on the Next button to go to the next window, and then click on the Finish button to confi rm this foreign key ’ s creation Your fi nished foreign key creation window for the Course table should match the one shown in Figure 2.63

2.11.3.4 Create Constraints Between Student Course and Student Tables

The relationship between the Student table and the StudentCourse table is a one - to - many relationship The primary key student_id in the Student table is a foreign key in the

Figure 2.62 Create the foreign key between the Course and the Faculty table

StudentCourse table since one student can take multiple different courses In order

to create this relationship by using the foreign key, fi rst let ’ s open the StudentCourse table

Click on the Constraints tab and then click the Create button that is the fi rst button

on the second row Enter STUDENTCOURSE_STUDENT_FK into the Constraint Name box, and select the Foreign Key from the Constraint Type box, which is shown in Figure 2.64 Check the On Delete Cascade checkbox Then select the STUDENT_ID from the StudentCourse table as the foreign key column Select the STUDENT table from the Reference Table Name box as the reference table, and select the STUDENT_ID from the Reference Table Column List as the reference table column Your fi nished Add Constraint window should match the one shown in Figure 2.64

Click on the Next button to go to the next window, and then click on the Finish button to confi rm this foreign key ’ s creation

2.11.3.5 Create Constraints Between Student Course and Course Tables

The relationship between the Course table and the StudentCourse table is a one - to - many relationship The primary key course_id in the Course table is a foreign key in the StudentCourse table since one course can be taken by multiple different students By using the StudentCourse table as an intermediate table, a many - to - many relationship can

be built between the Student table and the Course table

To create this relationship by using the foreign key, open the StudentCourse table

by clicking on it from the left pane Click the Constraints tab and then click on the Create button that is the fi rst button on the second row Enter STUDENTCOURSE_

COURSE_FK into the Constraint Name box, and select the Foreign Key from the Constraint Type box, which is shown in Figure 2.65 Check the On Delete Cascade check-box Then select the COURSE_ID from the StudentCourse table as the foreign key column Select the COURSE table from the Reference Table Name box as the refer-ence table, and select the COURSE_ID from the Reference Table Column List as the

Figure 2.63 Finished foreign key creation window for the Course table

2.11 Create Oracle 10g XE Sample Database 85

Figure 2.65 Create the foreign key between the StudentCourse and the Course table

Figure 2.64 Create the foreign key between the StudentCourse and the Student table

reference table column Your fi nished Add Constraint window should match the one shown in Figure 2.65

Click on the Next button to go to the next window, and then click on the Finish button to confi rm this foreign key ’ s creation Your fi nished foreign key creation window for the StudentCourse table should match the one shown in Figure 2.66

Our customer database creation for Oracle Database 10g Express Edition is pleted A completed Oracle 10g XE sample database CSE_DEPT that is represented by

com-a group of tcom-able fi les ccom-an be found in the folder Orcom-acle loccom-ated com-at the com-accompcom-anying ftp

web site (see Chapter 1 ) Refer to Appendix F to get more detailed information if you want to use this sample database in your Visual C# applications

At this point, we have fi nished developing and creating all sample databases we need

to use later All of these sample databases will be utilized for different applications we will develop in this book

Since the Oracle Database 10g XE is very different with other databases such as Microsoft Access and SQL Server 2005, you need to refer to Appendix F to get a clear picture about how to use the CSE_DEPT Oracle database fi les Refer to Appendix D to get the knowledge on how to use the Utilities of Oracle Database 10g XE to Unload the

fi ve tables to fi ve Text fi les, and how to Load those fi ve table fi les into a new customer Oracle database to create a new customer Oracle database easily

A detailed discussion and analysis of the structure and components about databases were provided in this chapter Some key technologies in developing and designing databases were also given and discussed The procedures and components to develop a relational database were analyzed in detailed with some real data tables in our sample database CSE_DEPT The process in developing and building a sample database was discussed in detail with the following points:

• Defi ning relationships

• Normalizing the data

• Implementing the relational database

Figure 2.66 Finished foreign key creation window for the StudentCourse table

Homework 87

In the second part of this chapter, three sample databases that were developed with three popular database management systems such as Microsoft Access, SQL Server 2005, and Oracle Database 10g XE were provided in detail All of these three sample databases will be used throughout the whole book

HOMEWORK

I True/False Selections

1 Database development process involves project planning, problem analysis, logical design,

physical design, implementation, and maintenance

2 Duplication of data creates problems with data integrity

3 If the primary key consists of a single column, then the table in 1NF is automatically in

2NF

4 A table is in fi rst normal form if there are no repeating groups of data in any column

5 When a user perceives the database as made up of tables, it is called a Network Model

6 Entity integrity rule states that no attribute that is a member of the primary (composite) key

may accept a null value

7 When creating data tables for the Microsoft Access database, a blank fi eld can be kept as

a blank without any letter in it

8 To create data tables in SQL Server database, a blank fi eld can be kept as a blank without

any letter in it

9 The name of each data table in SQL Server database must be prefi xed by the keyword dbo

_ 10 The Sequence object in Oracle database is used to automatically create a sequence of

numeric numbers that work as the primary keys

II Multiple Choices

1 There are many advantages to using an integrated database approach over that of a fi le

pro-cessing approach These include

a Minimizing data redundancy

b Improving security

c Data independence

d All of the above

2 The entity integrity rule implies that no attribute that is a member of the primary key may

accept _

a Null value

b Integer data type

c Character data type

d Real data type

3 Reducing data redundancy will lead to _

a Deletion anomalies

b Data consistency

c Loss of effi ciency

d None of the above

4 keys are used to create relationships among various tables in a database

a Primary keys

b Candidate keys

c Foreign keys

d Composite keys

5 In a small university the Department of Computer Science has six faculty members However,

each faculty member belongs to only the Computer Science Department This type of ship is called _

relation-a One - to - one

b One - to - many

c Many - to - many

d None of the above

6 The Client Server databases have several advantages over the File Server databases These

include

a Minimizing chances of crashes

b Provision of features for recovery

c Enforcement of security

d Effi cient use of the network

e All of the above

7 One can create the foreign keys between tables

a Before any table can be created

b When some tables are created

c After all tables are created

d With no limitations

8 To create foreign keys between tables, fi rst one must select the table that contains a _

key and then select another table that has a _ key

Homework 89

III Exercises

1 What are the advantages to using an integrated database approach over that of a fi le processing

approach?

2 Defi ne entity integrity and referential integrity Describe the reasons for enforcing these rules

3 Entities can have three types of relationships: one - to - one, one - to - many, and many - to - many

Defi ne each type of relationship Draw ER diagrams to illustrate each type of relationship

4 List all steps to create foreign keys between data tables for SQL Server database in the SQL

Server Management Studio Express Illustrate those steps by using a real example For instance, how to create foreign keys between the LogIn and the Faculty table

5 List all steps to create foreign keys between data tables for Oracle database in the Oracle

Database 10g XE Illustrate those steps by using a real example For instance, how to create foreign keys between the StudentCourse and the Course table

Chapter 3

Introduction to ADO NET

It has been a long road for software developers to generate and implement sophisticated data processing techniques to improve and enhance data operations The evolution of data access Application Programming Interface (API ) is also a long process focusing predominantly on how to deal with relational data in a more fl exible way The methodol-ogy development has been focused on Microsoft - based APIs such as Open Database Connectivity (ODBC), OLEDB , Microsoft Jet, Data Access Objects (DAO), and Remote Data Objects (RDO), in addition to many non - Microsoft - based APIs These APIs did not bridge the gap between object - based and semistructured (XML) data programming needs Combine this problem with the task of dealing with many different data stores, nonrelational data like XML and applications applying across multiple languages are challenging topics, and one should have a tremendous opportunity for complete rearchi-tecture The ADO.NET is a good solution for these challenges

ADO.NET 2.0 was considered as a full solution between the relational database API and object - oriented data access API, which was released with the NET Framework 2.0 and Visual Studio.NET 2005 Today the updated version of the ADO.NET is 3.5, which

is released with the NET Framework 3.5 and Visual Studio.NET 2008 In this chapter,

fi rst we will provide a detailed review about the history of ADO.NET, and then a full discussion and description about the components and architectures of ADO.NET 2.0 is given since most data components used for today ’ s database actions are still covered by the ADO.NET 2.0 Finally we introduce some new features and components included in the ADO.NET 3.5

ActiveX Data Object (ADO) is developed based on Object Linking and Embedding (OLE) and Component Object Model (COM) technologies COM is used by developers

to create reusable software components, link components together to build applications, and take advantage of Windows services For the last decade, ADO has been the pre-

Practical Database Programming With Visual C#.NET, by Ying Bai

Copyright © 2010 the Institute of Electrical and Electronics Engineers, Inc.

ferred interface for Visual Basic programmers to access various data sources, with ADO 2.7 being the latest version of this technology The development history of data accessing methods can be traced back to the mid - 1990s with DAO and then followed by RDO, which was based on ODBC In the late 1990s, the ADO that is based on OLEDB was developed This technology is widely applied in most object - oriented programming and database applications during the last decade

ADO.NET 3.5 is the updated version of ADO.NET, and it is based mainly on the Microsoft NET Framework 3.5 The underlying technology applied in ADO.NET 3.5 is very different from the COM - based ADO The ADO.NET Common Language Runtime provides bidirectional, transparent integration with COM This means that COM and ADO.NET applications and components can use functionality from each system But the ADO.NET 3.5 Framework provides developers with a signifi cant number of benefi ts including a more robust, evidence - based security model, automatic memory management native Web services support, and Language Integrated Query (LINQ) For new develop-ment, the ADO.NET 3.5 is highly recommended as a preferred technology because of its powerful managed runtime environment and services

This chapter will provide a detailed introduction to ADO.NET 2.0 and ADO.NET 3.5 and their components, and these components will be utilized for the rest of the book

In this chapter, you will:

• Learn the basic classes in ADO.NET 2.0 and its architecture

• Learn the different ADO.NET 2.0 data providers

• Learn about the Connection and Command components

• Learn about the Parameters collection component

• Learn about the DataAdapter and DataReader components

• Learn about the DataSet and DataTable components

• Learn about the ADO.NET 3.5 Entity Framework (EF)

• Learn about the ADO.NET 3.5 Entity Framework Tools (EFT)

• Learn about the ADO.NET Entity Data Model (EDM)

First let ’ s take a closer look at ADO.NET 2.0 and have a global picture of its components

ADO.NET is a set of classes that expose data access services to the Microsoft NET programmer ADO.NET provides a rich set of components for creating distributed, data - sharing applications It is an integral part of the Microsoft NET Framework, providing access to relational, XML, and application data ADO.NET supports a variety of devel-opment needs, including the creation of front - end database clients and middle - tier busi-ness objects used by applications, tools, languages, or Internet browsers

All ADO.NET classes are located at the System.Data namespace with two fi les named System.Data.dll and System.Xml.dll When compiling code that uses the System.Data namespace, reference both System.Data.dll and System.Xml.dll

3.3 Architecture of ADO.NET 2.0 93

Basically speaking, ADO.NET provides a set of classes to support you to develop database applications and enable you to connect to a data source to retrieve, manipulate, and update data with your database The classes provided by ADO.NET are core to develop a professional data - driven application, and they can be divided into the following three major components:

Data Provider contains four classes: Connection, Command, DataAdapter, and DataReader These four classes can be used to perform the different functionalities to help you to:

1 Set a connection between your project and the data source using the Connection object

2 Execute data queries to retrieve, manipulate, and update data using the Command object

3 Move the data between your DataSet and your database using the DataAdapter object

4 Perform data queries from the database (read - only) using the DataReader object

The DataSet class can be considered as a table container and it can contain multiple data tables These data tables are only a mapping to those real data tables in your data-base But these data tables can also be used separately without connecting to the DataSet

In this case, each data table can be considered as a DataTable object

The DataSet and DataTable classes have no direct relationship with the Data Provider class; therefore they are often called Data Provider – independent components Four classes such as Connection, Command, DataAdapter, and DataReader that belong to Data Provider are often called Data Provider – dependent components

To get a clearer picture of the ADO.NET, let ’ s fi rst take a look at the architecture

of the ADO.NET

3.3 ARCHITECTURE OF ADO NET 2.0

The ADO.NET 2.0 architecture can be divided into two logical pieces: command tion and caching Command execution requires features like connectivity, execution, and reading of results These features are enabled with ADO.NET Data Providers Caching

execu-of results is handled by the DataSet

The Data Provider enables connectivity and command execution to underlying data sources Note that these data sources do not have to be relational databases Once a command has been executed the results can be read using a DataReader A DataReader provides effi cient forward - only stream - level access to the results In addition, results can

be used to render a DataSet a DataAdapter This is typically called “ fi lling the DataSet ” Figure 3.1 shows a typical architecture of the ADO.NET 2.0

In this architecture, the data tables are embedded in the DataSet as a DataTableCollection and the data transactions between the DataSet and the Data

Provider such as SELECT, INSERT, UPDATE, and DELETE are made by using the DataAdapter via its own four different methods: SelectCommand, InsertCommand, UpdateCommand, and DeleteCommand, respectively The Connection object is only used to set a connection between your data source and your applications The DataReader object is not used for this architecture As you will see from the sample project in the following chapters, to execute the different methods under the DataAdapter to perform the data query is exactly to call the Command object with different parameters

Another ADO.NET architecture is shown in Figure 3.2 In this architecture, the data tables are not embedded into the DataSet but treated as independent data tables, and each table can be considered as an individual DataTable object The data transactions between the Data Provider and the DataTable are realized by executing the different methods of the Command object with the associated parameters The ExecuteReader() method of the Command object is called when a data query is made from the data source, which is equivalent to executing an SQL SELECT statement, and the returned data should be stored to the DataReader object When performing other data - accessing opera-tions such as INSERT, UPDATE, or DELETE, the ExecuteNonQuery() method of the

Connection Command DataReader

DataSet Data Provider

DataTableCollection

ConstraintCollection

DataTable

DataRowCollection DataColumnCollection

DataRelationCollection

Your Application

Figure 3.1 Typical architecture of ADO.NET 2.0

Connection DataAdapter DataReader

DataSet

DataRelationCollection ConstraintCollection

DataTable

DataRowCollection DataColumnCollection

Your Application

Figure 3.2 Another architecture of ADO.NET 2.0

3.4 COMPONENTS OF ADO NET 2.0

As we discussed in Section 3.2 , ADO.NET 2.0 is composed of three major components:

Data Provider, DataSet, and DataTable First let ’ s take a look at the Data Provider

3.4.1 Data Provider

The Data Provider can also be called a data driver, and it can be used as a major ponent for your data - driven applications The functionalities of the Data Provider, as its name means, are to:

• Connect your data source with your applications

• Execute different methods to perform the associated data query and data - accessing tions between your data source and your applications

• Disconnect the data source when the data operations are done

The Data Provider is physically composed of a binary library fi le, and this library is

in the DLL fi le format Sometimes this DLL fi le depends on other DLL fi les, so in fact

a Data Provider can be made up of several DLL fi les Based on the different kinds of databases, Data Provider can have several versions and each version is matched to each kind of database The popular versions of the Data Provider are:

• O pen D ata B ase C onnectivity ( Odbc ) Data Provider (ODBC.NET)

• O bject L inking and E mbeding D ata B ase ( OleDb ) Data Provider (OLEDB.NET)

• SQL Server ( Sql ) Data Provider (SQL Server.NET)

• Oracle ( Oracle ) Data Provider (Oracle.NET)

Each Data Provider can be simplifi ed by using an associated keyword, shown in bold

in the parentheses above For instance, the keyword for the ODBC Data Provider is Odbc; the keyword for an SQL Server Data Provider is Sql, and so on

In order to distinguish from the older Data Providers such as Microsoft ODBC, Microsoft OLE DB, Microsoft SQL Server, and Oracle, in some books all different Data Providers included in the ADO.NET are extended by a suffi x NET, such as OLE DB.NET, ODBC.NET, SQL Server.NET, and Oracle.NET Since most Data Providers discussed in this book belong to ADO.NET, generally we do not need to add the NET suffi x but we will add this suffi x if the old Data Providers are used

The different Data Providers are located at the different namespaces, and these namespaces hold the various data classes that you must import into your code in order

to use those classes in your project

Table 3.1 lists the most popular namespaces used by the different Data Providers and used by the DataSet and the DataTable

Since a different Data Provider is located at the different namespace as shown in Table 3.1 , you must fi rst add the appropriate namespace into your Visual C#.NET 2008 project, exactly into each form ’ s code window, whenever you want to use that Data Provider Also all classes provided by that Data Provider must be prefi xed by the associ-ated keyword For example, you must use “ using System.Data.OleDb ” to add the namespace of the OLEDB.NET Data Provider if you want to use this Data Provider in your project, and also all classes belonging to that Data Provider must be prefi xed by the associated keyword OleDb, such as OleDbConnection, OleDbCommand, OleDbDataAdapter, and OleDbDataReader The same thing holds true for all other Data Providers

Although different Data Providers are located at the different namespaces and have the different prefi xes, the classes of these Data Providers have the similar methods or properties with the same name For example, no matter what kind of Data Provider you are using such as an OleDb, an Sql, or an Oracle, they have the methods or properties with the same name, such as Connection String property, Open() and Close() methods,

as well as the ExecuteReader() method This provides fl exibility for the programmers and allows them to use different Data Providers to access the different data sources by only modifying the prefi x applied before each class

The following sections provide a more detailed discussion for each specifi c Data Provider These discussions will give you a direction or guideline to help you to select the appropriate Data Provider when you want to use them to develop the different data - driven applications

3.4.1.1 ODBC Data Provider

The NET Framework Data Provider for ODBC uses native ODBC Driver Manager (DM) through COM interop to enable data access The ODBC Data Provider supports both local and distributed transactions For distributed transactions, the ODBC Data Provider, by default, automatically enlists in a transaction and obtains transaction details from Windows 2000 Component Services

The ODBC.NET Data Provider provides access to ODBC data sources with the help

of native ODBC drivers in the same way that the OleDb.NET Data Provider accesses native OLE DB providers

Table 3.1 Namespaces for Different Data Providers, Data S et, and Data T able

System.Data Holds the DataSet and DataTable classes

System.Data.OleDb Holds the class collection used to access an OLEDB data

3.4 Components of ADO.NET 2.0 97

The ODBC.NET supports the following Data Providers:

• SQL Server

• Microsoft ODBC for Oracle

• Microsoft Access Driver ( * mdb)

Some older database systems only support ODBC as the data access technique, which include older versions of SQL Server and Oracle as well as some third - party database such as Sybase

3.4.1.2 OLEDB Data Provider

The System.Data.OleDb namespace holds all classes used by the NET Framework 2.0 Data Provider for OLE DB The NET Framework Data Provider for OLE DB describes

a collection of classes used to access an OLE DB data source in the managed space Using the OleDbDataAdapter, you can fi ll a memory - resident DataSet that you can use to query and update the data source The OLE DB.NET data access technique supports the following Data Providers:

• Microsoft Access

• SQL Server (7.0 or later)

• Oracle (9i or later)

One advantage of using the OLEDB.NET Data Provider is to allow users to develop

a generic data - driven application The so - called generic application means that you can use the OLEDB.NET Data Provider to access any data source such as Microsoft Access, SQL Server, Oracle, and other data sources that support the OLEDB

Table 3.2 shows the compatibility between the OLEDB Data Provider and the OLE DB.NET Data Provider

3.4.1.3 SQL Server Data Provider

This Data Provider provides access to a SQL Server version 7.0 or later database using its own internal protocol The functionality of the Data Provider is designed to be similar

to that of the NET Framework Data Providers for OLE DB, ODBC, and Oracle All classes related to this Data Provider are defi ned in a DLL fi le and located at the System

Data.SqlClient namespace Although Microsoft provides different Data Providers to access the data in the SQL Server database, such as the ODBC and OLE DB, for the sake of optimal data operations, it is highly recommended to use this Data Provider to access the data in an SQL Server data source

Table 3.2 Compatibility between OLEDB and OLEDB NET

SQLOLEDB Used for Microsoft SQL Server 6.5 or earlier Microsoft.Jet.OLEDB.4.0 Used for Microsoft JET database (Microsoft Access) MSDAORA Used for Oracle version 7 and later