ADO.NET Data Access

Page  2 SQL  When we interact with the datasource through ADO.NET we use the SQL language to retrieve,modify,update information  Structured Query Language is a standard data access language used to interact with relational database  SQL Select Statement  Update Statement  Insert Statement  Delete Statement

Page  3 SQL Select Statement  To retrieve one or more rows of data the select command is used SELECT [columns] FROM [tables] WHERE [search_condition] ORDER BY [order_expression ASC | DESC]

Page  4 Sample Select Statement (eg) SELECT * FROM Authors  (*) - retrieves all the columns from the table  The FROM clause identifies that the Author table is being used  There is no WHERE clause, means all the records will be retrieved  There is no ORDER BY clause, means the data’s are not sorted

Page  5 Improving the Select Statement SELECT lname,fname FROM Authors WHERE State =‘MI’ ORDER BY lname ASC  Only two columns are retrieved  WHERE Clause provides the restriction to a particular state  An ORDER BY clause sorts the lname alphabetically in ascending order

Page  6 The WHERE clause (eg)SELECT * FROM Sales WHERE ord_date ‘1987/01/01’  Multiple conditions can be combined using the AND keyword  Greater than and Less than comparisons can be made using symbols

Page  7 SQL Update Statement  Syntax: Eg UPDATE Authors SET lname=‘Gowri’ WHERE id =‘101’ UPDATE [table] SET [update_epression] WHERE [search_condition]

Page  8 SQL Insert Statement  Syntax Eg INSERT INTO Authors (lname,fname) VALUES (‘John’,’Khan’) INSERT INTO [table] ([column_list]) VALUES ([value_list])

Page  9 The SQL Delete Statement  Syntax  Eg DELETE FROM Authors WHERE id=‘102 DELETE FROM [table] WHERE [search_condition]

Page  10 Simple Data Access  To retrieve information with simple Data Access follow these steps  Create Connection,Command,DataReader objects  Use DataReader to retrieve information from the database and display it in a control in the webform  Close your connection  Send the page to the user.At this point all the connections have been closed

Page  11 Importing Namespaces  Imports System.Data  Imports System.Data.OleDb (OR)  Imports System.Data.SqlClient

Page  12 Creating a connection  The first step is to make a connection with the database  Specify a value for the ConnectionString property  This property defines all the information the computer needs to find the data source,log in and initial database

Page  13 The Connection String  The ConnectionString is actually a series of distinct pieces of information,separated by semicolons(;)  Provider –This refers to the name of the Provider which allows communication between ADO.NET and database (SQLOLEDB is the provider for SQL)  Data Source – This refers to the name of the server where the data source is located;Server is on the same computer so localhost

Page  14 The Connection String  Initial CataLog – It refers to the name of the initial database  User ID – Used to access the database,sa refers to the system admin account  Password - By default the ‘sa’ account does not have a password  ConnectionTimeout – It determines how long your code will wait in seconds before generating an error if it cannot establish connection default 15 seconds

Page  15 SQl Server Integrated Authentication  With SQL Server Authentication SQL Server maintains its own user account With integrated authentication SQL Server automatically uses the windows account information for the currently logged in user

Page  16 Making the connnection

Page  17 Defining a select command  The connection object a few basic properties that give the information about the connection  An SQL Statement that selects the information you want (eg) SELECT * from Authors  A command object that executes the SQL statement SqlDataAdapter adap=new SqlDataAdapter(“SELECT * from Author”,con)  A DataSet object to store the retrieved objects (eg)DataSet ds=new DataSet()