12. Data Access using ADO.Net

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ADO.Net Disconnected Data Access Architecture

Another important aspect of disconnected architecture is that it maintains a local repository of data in the dataset object. The dataset object stores the tables, their relationship and their different constraints. The user can perform operations like update, insert and delete on this dataset locally, and the changes made to the dataset are applied to the actual database as a batch when needed. This greatly reduces network traffic and results in better performance.

Different components of ADO.Net

Before going into the details of implementing data access applications using ADO.Net, it is important to understand its different supporting components or classes. All generic classes for data access are contained in the System.Data namespace.

ADO.Net also contains some database specific classes. This means that different database system providers may provide classes (or drivers) optimized for their particular database system. Microsoft itself has provided the specialized and optimized classes for their SQL server database system. The name of these classes start with 'Sql' and are contained in the System.Data.SqlClient namespace.

Similarly, Oracle has also provides its classes (drivers) optimized for the Oracle DB System. Microsoft has also provided the general classes which can connect your application to any OLE supported database server. The name of these classes start with 'OleDb' and these are contained in the System.Data.OleDb namespace. In fact, you can use OleDb classes to connect to SQL server or Oracle database; using the database specific classes generally provides optimized performance, however.

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A review of basic SQL queries

Here we present a brief review of four basic SQL queries.

SQL SELECT Statement

This query is used to select certain columns of certain records from one or more database tables.

SELECT * from emp

selects all the fields of all the records from the table named 'emp'

SELECT empno, ename from emp

selects the fields empno and ename of all the records from the table named 'emp'

SELECT * from emp where empno < 100

selects all those records from the table named 'emp' where the value of the field empno is less than 100

SELECT * from article, author where article.authorId = author.authorId

selects all those records from the tables named 'article' and 'author' that have the same value of the field authorId

SQL INSERT Statement

This query is used to insert a record into a database table.

INSERT INTO emp(empno, ename) values(101, 'John Guttag')

inserts a record in to the emp table and set its empno field to 101 and its ename field to 'John Guttag'

SQL UPDATE Statement

This query is used to modify existing records in a database table.

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UPDATE emp SET ename = 'Eric Gamma' WHERE empno = 101

updates the record whose empno field is 101 by setting its ename field to 'Eric Gamma'

SQL DELETE Statement

This query is used to delete existing record(s) from a database table.

DELETE FROM emp WHERE empno = 101

deletes the record whose empno field is 101 from the emp table

Performing common data access tasks with ADO.Net

Enough review and introduction! Let's start something practical. Now we will build an application to demonstrate how common data access tasks are performed using ADO.Net.

We will use the MS SQL server and MS Access database systems to perform the data access tasks. SQL Server is used because probably most of the time you will be using MS SQL server when developing .Net applications.

For SQL server, we will be using classes from the System.Data.SqlClient namespace. Access is used to demonstrate the OleDb databases. For Access we will be using classes from the System.Data.OleDb namespace.

In fact, there is nothing different in these two approaches for developers and only two or three statements will be different in both cases. We will highlight the specific statements for these two using comments like:

// For SQL server

SqlDataAdapter dataAdapter = new

SqlDataAdapter(commandString, conn);

// For Access

OleDbDataAdapter dataAdapter = new

OleDbDataAdapter(commandString, conn);

For the example code, we will be using a database named 'ProgrammersHeaven'. The database will have a table named 'Article'. The fields of the table 'Article' are: