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 Browser Web Server HTTP Request This is a web page Browser interprets HTML and displays page This is a web page Picture HTTP Response

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 Client Web Server HTTP Request site Stars John Wayne Meg Ryan Interprets script code Performs action Fills in part of page Sends response to client Stars John Wayne MegRyan Browser interprets HTML and displays page Gets 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… Hardware Operating System Common Language Runtime (CLR) Your Application.NET Framework Class Library VBJ#C#C++…

CLR-based execution.NET applications are not stand-alone executable programs APP.exe other FxCL components CLR JIT Compiler obj code OS Process Underlying OS and HW Core FxCL

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 ? Win64Win32 ( 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 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 data reader quick and simple read only ADO.NET dataset tables and relationships reading and writing ADO.NET command specifies data to send or receive ADO.NET connection Specifies data source, provider, security information SQL Server ADO.NET data adapter – reading, writing

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 DataSet myStars WebForm DataGrid DataAdapter SelectCommand

Example program from handout (cont.) Hollywood MovieStar Connection DataSet myStars WebForm DataGrid DataAdapter SelectCommand this.sqlDataAdapter1.Fill(dataSet11,”myStars”);

Example program from handout (cont.) Hollywood MovieStar Connection DataSet myStars WebForm DataGrid DataAdapter SelectCommand 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(); }