1. PROG11044 - Advanced Web Apps
5/23/2018
Notes on ADO.NET (1)
Wendi Jollymore, ACES

2. Review So Far Software we used:
Microsoft SQL Server Express
Microsoft SQL Server Management Studio
Web Developer or Visual Studio
We created a Database called KaluhaBooks
Authors, Categories, and Books tables
See the database diagrams for an overview
5/23/2018
Wendi Jollymore, ACES

3. Review So Far Database Accounts: sa Your guest account
the system admin account we use in the Server Management software to work with out database
Your guest account
The account you’ll use for visitors to your data pages
This account was given permission to run select, delete, update, and insert queries on the data in the database
5/23/2018
Wendi Jollymore, ACES

4. Review So Far Simple data page SqlDataSource control GridView control
“quick and dirty” way to create a connection to a database
GridView control
Shows data in rows and columns
Paging, sorting
AutoGenerateColumns: turn this off to add the columns yourself
5/23/2018
Wendi Jollymore, ACES

5. Web-Based Database Apps
Recall that the web is stateless
This changes how database applications function on the web
Typical Database App:
User accesses the database
They make changes to the data
They close the database or database connection
5/23/2018
Wendi Jollymore, ACES

6. Web-Based Database Apps
Web Database Apps:
Connection to the database is made by client machine
A copy of the desired data is retrieved and downloaded to client machine
Connection to database is closed
Client user makes changes to data.
Client connects to database and applies the changes
Connection to database is closed and a new connection created.
A new and refreshed copy of the data is retrieved and downloaded to the client machine.
The connection is closed.
5/23/2018
Wendi Jollymore, ACES

7. Web-Based Database Apps
Thankfully, many web pages will only be allowing a user to view records, not update/delete/insert records
We will still learn to handle data manipulation
But we’ll start by learning the anatomy of the various components of ADO.NET and data-driven web applications
5/23/2018
Wendi Jollymore, ACES

8. Database Connections
Open (or recreate) the first example from the last class
Examine the markup for this page.
Look for the markup for the data source control:
<asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:KaluhaBooksConnectionString %>“ SelectCommand="SELECT * FROM [Authors]">
</asp:SqlDataSource>
5/23/2018
Wendi Jollymore, ACES

9. Database Connections Look at the markup for the GridView control:
DataSourceID property points to the name of the data source control
See the <Columns> </Columns> tags
So far, we haven’t written any code.
We will do this today!
5/23/2018
Wendi Jollymore, ACES

10. Database Connections Connection Strings
Recall in the markup for the Sql data source control you saw:
ConnectionString="<%$ ConnectionStrings:KaluhaBooksConnectionString %>“
This is referring to a variable in the Web.Config file
Open the Web.Config file for the project
5/23/2018
Wendi Jollymore, ACES

11. Database Connections
<connectionStrings>
<add name="KaluhaBooksConnectionString"
connectionString="Data Source=l-userdude\sqlexpress;
Initial Catalog=KaluhaBooks; Persist Security Info=True;
User ID=userGuest; Password=ungabunga"
providerName="System.Data.SqlClient"/>
</connectionStrings>
The connectionStrings element contains one or more connection strings that define the connection to the database
The add element defines a single connection string
5/23/2018
Wendi Jollymore, ACES

12. Connection String Properties
Provider
This is the database software, or data provider, that you'd like to use.
we're using System.Data.SqlClient.
If you were using a different kind of database, such as an .MDB file or MySql database, your provider name would be different.
Data Source/Server/Address
the name of the server/instance, network address, or location of the data source.
Initial Catalog/Database
the name of a database to use when the connection is made.
5/23/2018
Wendi Jollymore, ACES

13. Connection String Properties
User ID/UID
the user name used for logging into the database, if applicable.
Password/PWD
the password used to log into the database, if applicable.
Connection Timeout
Number of seconds until timeout if there’s a problem connecting
default is 15 seconds; never change this to 0!
having a timeout of 0 will cause the connection to hang indefinitely!
Persist Security Info
true if security information is returned with the connection; false if not.
In most cases, this should always be false!!
5/23/2018
Wendi Jollymore, ACES

14. Connection String in Web.Config
In the Web.Config file’s connectionStrings element:
providerName attribute was used
This was automatically generated when we added the Sql Data Source control
Normally you would not include this
You will be coding the connections by hand
You’ll include the statement:
using System.Data.SqlClient;
5/23/2018
Wendi Jollymore, ACES

15. Exercise Start up a new web project.
Add a new Web.Config file to the project:
Right-click on the top node of your project
From the dialog select Web Configuration File and click the Add button
In your project, open the Web.Config file
5/23/2018
Wendi Jollymore, ACES

16. Exercise Locate the <configuration> section You should see the
<connectionStrings /> tag
Replace it with:
<connectionStrings>
<add name="SqlConnectionString“ connectionString=
"Data Source=L-USERDUDE\SQLEXPRESS;
Initial Catalog=KaluhaBooks; User ID=yourguest;
Password=yourguestpw" />
</connectionStrings>
Then go to your source code and add:
using System.Data.SqlClient;
5/23/2018
Wendi Jollymore, ACES

17. Exercise In the Page_Load event, get the connection string:
string connString = ConfigurationManager.ConnectionStrings["SqlConnectionString"].ConnectionString;
ConfigurationManager
Contains config information in the Web.Config file
ConnectionStrings property contains the array of elements added to the <connectionStrings> element
Access one of the elements by the name you gave it in the web.config file
The last ConnectionString property corresponds to the same item in the <add> element.
5/23/2018
Wendi Jollymore, ACES

18. Connection Pooling
Why put the connection string in the web.config file?
When you connect to a database, many things happen
Parsing of connection string and its properties
Authentication
Locate data source
..and lots of other stuff!
Takes up a lot of processing time and bandwidth!
5/23/2018
Wendi Jollymore, ACES

19. Connection Pooling Some providers support connection pooling:
When a connection is “closed”, it’s put aside into a connection pool
When a new connection is needed, the provider checks the pool.
If one matches, it uses that instead of creating a new one.
This is much faster, and is a lot less work.
SqlClient supports connection pooling.
5/23/2018
Wendi Jollymore, ACES

20. Connection Pooling
For connection pooling to work, connections need to match exactly.
E.g.
Data Source=mycrapbox\sqlexpress; Initial Catalog=KaluhaBooks; User ID=ungabunga; Password=whatevah
Server=mycrapbox\sqlexpress; Database=KaluhaBooks; User ID=ungabunga; Password=whatevah
These connections are the same, in our eyes!
The syntax is different!
According to the provider, they do not match!
5/23/2018
Wendi Jollymore, ACES

21. Connection Pooling
By putting your connection string info in the web.config file:
You will always use that exact connection string each and every time.
When an unused connection goes into the connection pool, it will be a perfect match for all other connections you will need
This will make your program faster!
5/23/2018
Wendi Jollymore, ACES

22. Classes Used in ADO.NET SqlConnection
Models the actual connection to a database.
Like an input/output stream in Java.
Must be opened and closed to be used.
Has Open() and Close() methods.
Has a ConnectionString property that contains the connection string information
5/23/2018
Wendi Jollymore, ACES

23. Classes Used in ADO.NET SqlCommand
Models a command that can be executed over a specific connection.
Connection property
References the connection object that this command should use.
CommandText property
Contains the SQL command to execute.
Can be a query, or insert/update/delete statement.
Can be a stored procedure or table name.
See also CommandType property
5/23/2018
Wendi Jollymore, ACES

24. Classes Used in ADO.NET SqlCommand continued ExecuteQuery() method
Used to execute an SQL Select query
Returns a DataReader object
DataReaders can be used as a data source for controls like the GridView and ListBox
ExecuteScalar() method
Used to execute an SQL command that returns a single value
E.g. using a Max() or Count() function
5/23/2018
Wendi Jollymore, ACES

25. Classes Used in ADO.NET SqlCommand continued ExecuteNonQuery() method
Used to execute an SQL statement that is not a Select query
E.g. update, insert, or delete statement
Returns an integer  number of rows affected
5/23/2018
Wendi Jollymore, ACES

26. Classes Used in ADO.NET SqlDataReader
Models set of records returned by a query.
Forward-only
You can only move forward; you can’t move backward
Read() method moves to the next available record
Returns true if successful, false otherwise.
Read-only
You can’t change/update any of the data
A connection used by a data reader is not available until the data reader is closed.
Data readers are very fast and efficient!
5/23/2018
Wendi Jollymore, ACES

27. Exercise Set up your web page Add a GridView control
In the Page_Load event, create a string variable cmdText with the following SQL statement:
"SELECT * FROM Authors ORDER BY LastName, FirstName"
Create a new SqlConnection object
The constructor takes a connection string
5/23/2018
Wendi Jollymore, ACES

28. Exercise Create a new SqlCommand object Open the connection:
The constructor takes a command string and a connection object.
Open the connection:
connection.Open();
Assign the return value of the command object’s ExecuteReader() method to the grid’s DataSource property:
GridView1.DataSource = command.ExecuteReader();
5/23/2018
Wendi Jollymore, ACES

29. Exercise Invoke the grid’s DataBind() method Close the connection:
connection.Close();
Load the page into your browser.
5/23/2018
Wendi Jollymore, ACES

30. Data Binding GridView.DataSource property
References a data source used to populate the grid
Can be a hash table, data set, or data reader (e.g. SqlDataReader)
SqlCommand.ExecuteReader() returns an SqlDataReader object.
We assigned this to the DataSource property of the grid.
5/23/2018
Wendi Jollymore, ACES

31. Data Binding GridView.DataBind() method
Once you assign a data source, invoke DataBind()
This method retrieves the data and populates the grid
The whole process is called data binding
We say that “the grid is bound to the database”.
5/23/2018
Wendi Jollymore, ACES

32. Parameters Sometimes you will want to view only certain records
Records that match a certain criteria
E.g. only titles by a certain author, or only books in a certain category
In older web programs, you could allow the user to select a value, and then concatenate the value to a WHERE clause:
Select * from Authors Where LastName Like “ + txtSearchAuthor.Text
5/23/2018
Wendi Jollymore, ACES

33. Parameters
This kind of practice can open you up to SQL Injection Attacks.
E.g. a hacker who knows SQL and your database structure could enter into the text field:
*; Delete * From Authors;
When concatenated to your Sql statement, you get:
Select * from Authors Where LastName Like *; Delete * From Authors;
This will delete the records in your Authors table!
5/23/2018
Wendi Jollymore, ACES

34. Parameters ADO.NET uses Parameter objects to keep this from happening
SqlParameter class
Models a parameter used as a variable value in an Sql statement
ParameterName property:
The name of the parameter/variable used in the Sql query
SqlDbType property
The data type of the value this parameter will have
Value property
The parameter’s value that will be inserted into the Sql statement
5/23/2018
Wendi Jollymore, ACES

35. Parameters A command object has a Parameters property
This references a collection of Parameter objects
command.Parameters.Add(paramObj);
Adds a parameter object to the collection
5/23/2018
Wendi Jollymore, ACES

36. Exercise Do the tutorial in the notes: Ado.Net: Coding Data Pages
“Using Parameter Objects”
5/23/2018
Wendi Jollymore, ACES