Computer Science 317
Database Management
Introduction to Web Access to
Databases
The Plan
• I. Introduction
– General overview
– One simple approach
• II. .NET Overview
• III. ADO.NET Overview
• III. Examples with C#
Part I: Introduction
Why web access to database?
• Provides platform independent, remote
access to the database
– Data viewing
– Data gathering
Web Browsers and Servers
• Web browser - This is a program that runs
on your local PC (client). It allows you to
request web pages from an internet host.
• Web server - This is a program that runs on
the internet host computer (server). It takes
requests for web pages from clients and
delivers the pages back to the client.
HTML and HTTP
• HyperText Markup Language - Allows “marking
up” a document with tags specifying appearance
and structure.
• HyperText Transfer Protocol - Protocol used for
browsers to communicate with web servers.
Basically, this consists of “requests” from the
browser and “responses” from the server.
Typical HTTP Request
HTTP Response
<HTML>
<B> This is a web page </B>
<IMAGE> Picture</IMAGE>
</HTML>
Browser
This is a
web page
Web Server
HTTP Request
http://website/some.html
Browser interprets
HTML and displays
page
Typical HTML Request
• Client Side (Browser)
– Issues request for
HTML page
– Receives response
HTML page
– Interprets HTML and
creates web page
– Displays web page
– Work is done here
• Server Side
– Reads request from
client
– Finds page on server
– Sends response page to
client
– Essentially a file server
Scripting Languages
• Scripting languages - Allow us to add capability
to what’s provided by HTML. Allow parts of the
page to be built “on the fly”
• Client-side scripts - Script engine on client
machine builds parts of page when page is loaded
by browser (date is simple example)
• Server-side scripts - Script engine on server builds
parts of page before sending to client (database
query results for example).
Typical Server-Side Request
Interprets script code
Performs action
Fills in part of page
<HTML>
<H1> Stars </H1>
<B> John Wayne <BR>
Meg Ryan </B>
</HTML>
Sends response
to client
<HTML>
<% server script %>
</HTML>
Gets Page
Web Server
HTTP Request
http://web site
Client
Stars
John Wayne
MegRyan
Browser interprets
HTML and displays
page
Typical Server-Side Request
• Client Side (Browser)
– Issues request for
HTML page
– Receives response
HTML page
– Interprets HTML and
creates web page
– Displays web page
• Server Side
–
–
–
–
Reads request from client
Finds page on server
Interprets script code
Does work dictated by this
code (or has it done)
– Alters HTML file
– Sends response page to
client
Web Access of Database
• The database resides on the server.
• Web pages with scripts (or calls to scripts)
allows the user to send database requests to
the server.
• The server accesses the database to honor
the requests.
• Results can be returned on an html page.
• Actions can take place on the database.
So, what are the pieces we need?
•
•
•
•
•
Browser software on user machines
A machine for the server
Web server software on server
Database management system on server
Scripting/programming language for
accessing the database
• Drivers/interfaces for scripting language to
access the database
So, what are the pieces we use?
• Browser: Netscape or Internet Explorer
• Server machine: The Windows 2000 server that
happens to house the SQL server.
• Web server: Microsoft IIS
• Database management system: SQL Server
• Programming: C# (VB.NET?) creating ASP.NET
• Database interface: ADO.NET
Part II: .NET Overview
Architecture
• Multi-language, virtual machine driven…
VB
J#
C#
C++
…
Your Application
.NET Framework
Class Library
Common Language Runtime (CLR)
Operating System
Hardware
CLR-based execution
• .NET applications are not stand-alone executable
programs
APP.exe
OS Process
other FxCL
components
JIT Compiler
obj code
Core
FxCL
CLR
Underlying OS and HW
Implications?
1. Clients need CLR & FxCL to run .NET apps
–
–
–
–
available via Redistributable .NET Framework
two versions: v1.0 (2002) and v1.1 (2003)
20MB download
runs on 98 and above, NT (sp6a) and above
• included in Windows 2003, otherwise install via Windows update
2. Design trade-off…
+ managed execution (more secure, memory
protection, etc.)
+ portability
– slower execution?
Cross-platform
• Compiled .NET apps run on any supported
platform:
Your application
?
Win64
Win32
(XP,2K,98)
WinCE
Command-line development
• Option #1 is to use command-line tools…
• .NET Framework SDK
• free (100 MB)
• complete set of command-line tools and docs
• development supported on Windows NT, 2000, XP
Pro
• http://msdn.microsoft.com/net
• other platforms?
– FreeBSD / Mac OS X via Rotor (i.e. SSCLI)
– Linux via Mono project
– Unix via dotGNU project
Part II: ADO.NET Overview
Introduction to ADO.NET
• This is the layer that allows us to communicate with
the database.
• Everything is object oriented which is good
• Recall
– Objects are defined by classes
– Objects are instantiated by constructors that may have
parameters
– Objects have
• Properties or members that give them state
• Methods that give them behavior
• I will give some of the important classes (objects), and
some of the properties and methods.
• Much more is available through the Visual Studio
documentation.
ADO.NET Communications with SQL Server
Console Application
Interacts with Console
Window
Windows Application
Interacts with Windows
Form with controls
Web Application
ASP.NET page with
HTML, scripting, controls
ADO.NET dataset
tables and relationships
reading and writing
ADO.NET data reader
quick and simple read only
ADO.NET command
specifies
data to send or receive
ADO.NET data
adapter – reading,
writing
ADO.NET connection
Specifies data source, provider, security information
SQL Server
SqlConnection Object
• Represents a connection to an SQL database
– One member is a ConnectionString that
contains information needed to connect to the
database
– Open method to open the connection using the
connection string
– There is a constructor that has connection string
as parameter
– Close method
SqlCommand Object
• Represents a command (SQL, T-SQL, Stored
procedure) to execute against the database
– CommandType
• StoredProcedure
• Text
– CommandText
• Name of the stored procedure if type is StoredProcedure
• The SQL statement if type is Text
– Connection
– ExecuteReader method – sends CommandText to the
connection and creates an SqlDataReader
(Note: Does NOT open and close connection)
SqlDataReader Object
• Provides a means of reading a forward-only
stream of rows from a SQL Server database.
– Has properties like HasRows, FieldCount
– Methods for getting column values of current row,
depending on type.
– Read method to move to next row.
– Very efficient way and preferred if only reading
DataSet Object
• Datasets store data in a disconnected cache.
The structure of a dataset is similar to that of a
relational database; it exposes a hierarchical
object model of tables, rows, and columns. In
addition, it contains constraints and
relationships defined for the dataset.
SqlDataAdapter Object
• Represents a set of data commands that are
used to fill the DataSet and update a SQL
Server database.
–
–
–
–
–
SelectCommand
UpdateCommand
InsertCommend
DeleteCommand
Fill method to fill DataSet table with data from
SelectCommand
– Update method used to update data in the database
Example program from handout
• When you drug the table onto the webform:
– An SqlConnection and SqlDataAdapter were created
– The connection was set to the database of the table
– The SelectCommand of the adapter was set to select all
rows from the table
• Then you generated a DataSet object
• You created a DataGrid object on the form
– Set its DataSource to be the DataSet
– Set its DataMember to be a tablename
Example program from handout (cont.)
Hollywood
MovieStar
Connection
DataAdapter
SelectCommand
DataSet
myStars
WebForm
DataGrid
Example program from handout (cont.)
Hollywood
MovieStar
Connection
DataAdapter
SelectCommand
DataSet
myStars
WebForm
DataGrid
this.sqlDataAdapter1.Fill(dataSet11,”myStars”);
Example program from handout (cont.)
Hollywood
MovieStar
Connection
DataAdapter
SelectCommand
WebForm
DataSet
myStars
DataGrid
this.DataBind();
Example program from handout (cont.)
• Note: We’re only doing sequential read from the
database table
–
–
–
–
Don’t need DataSet and DataAdapter for this
Just need Connection and Command (and DataReader)
Drag connection and command objects to the form.
Set the connection string correctly for connection
object.
– Set Command’s connection and CommandText
Example program from handout (cont.)
private void Page_Load(object sender, System.EventArgs e)
{
this.sqlConnection1.Open();
this.DataGrid1.DataSource = this.sqlCommand1.ExecuteReader();
this.DataBind();
this.sqlConnection1.Close();
}
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Computer Science 317 Database Management