Transcript intro
ASP.NET
Rina Zviel-Girshin
Lecture 4
1
Overview
Data Binding
Data Providers
Data Connection
Data Manipulations
2
Web-Application Development
Hardware
components
Web software
components
Information
processing
Developer
tools
Database
server
Client’s
PC
Webserver
Web
browser
Network
OS
Input
Output
Processing
Storage
VBScript ASP
C# ASP.NET
SQL
DBMS
HTML XML
JavaScript CSS
DB Management
System
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ASP.NET and Data
Data access and reporting are very important to
web-based systems.
Usually data items received from DataBases.
ASP.NET framework includes a rich set of classes
(DataSet, DataReader) and
controls (DataGrid, Repeater, DataList, ListBox) to work
with database data.
Web-page designer has to connect/to bind data to
the control.
Data can be a single value, a list of values or a
collection of values.
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Data Binding
Data binding is a process of retrieving data from a
source and dynamically associating it to a property of
some visual element.
In web-based systems a visual element can be an
HTML tag or .NET control.
Exists 2 types of data binding:
simple
connection between one piece of data and a server control
and complex
binds a list control (ListBox) or iterative control (Repeater) to one
or more columns of data.
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Data Source
Usually data binding is performed to fill some list
with selectable items from an imported data source
Data is bind to the control via DataSource property.
The value of DataSource defines the data source and
initialized to collection of data items.
like an ArrayList, a HashTable, a database (DataReader,
DataView), an XML file or a script.
<asp:RadioButtonList id="rb" runat="server" />
and later in some script:
rb.DataSource=someArrayList
This is a logical link. Nothing happens.
Later a DataBind() method is called to load data
from associated data source.
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Simple Data Binding Example
<%@ Page Language="C#"%>
<script runat="server">
void Page_Load()
{
if(!Page.IsPostBack)
{
ArrayList countries=new ArrayList();
countries.Add("Norway");
countries.Add("Sweden");
countries.Add("France")
countries.Add("Israel")
ddl.DataSource=countries;
DataBind();
}
}
The Page_Load method runs
EVERY time the page is
loaded.
A postback of a page means posting back to the
same page.
You can differentiate between the page’s first
request and any postbacks by using the
Page.IsPostback property.
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Simple Data Binding Example
void displayMessage(Object s,EventArgs s){
lbl.text="Your favorite country is: " + ddl.SelectedItem.Text;
}
</script>
<html><body>
<form runat="server">
<asp:DropDownList id="ddl" runat="server"
AutoPostBack="True" onSelectedIndexChanged="displayMessage" />
<p><asp:label id="lbl" runat="server" /></p>
</form></body></html>
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Output
onSelectedIndexChanged
="displayMessage"
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DataBind() method
DataBind() is a method of the Page class and all
server controls.
When DataBind method on a parent control is called
it cascades to all of the children of the control.
Calling DataBind on the Page causes all data binding
expressions on the page to be evaluated.
DataBind() method causes all data binding
expressions on the page to be evaluated
evaluates all <%# %> expressions within the page
evaluates all data bound properties of the controls.
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DataBind() method
Syntax of calling DataBind on the Page:
Page.DataBind() or
DataBind()
DataBind is commonly called from the Page_Load
event.
protected void Page_Load(Object Src, EventArgs E)
{
DataBind(); // or Page.DataBind();
}
However it can be called from another procedure
(next example).
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Example
<html><head>
<script language="C#" runat="server">
void SubmitBtn_Click(Object sender, EventArgs e)
{
Page.DataBind();
}
</script>
</head><body>
<h3><font face="Verdana">Data binding to a property of another server control</font></h3>
<form runat="server" ID="Form1">
<asp:DropDownList id=“CityList" runat="server">
<asp:ListItem>Jerusalem</asp:ListItem>
<asp:ListItem>Haifa</asp:ListItem>
<asp:ListItem>Tel-Aviv</asp:ListItem>
<asp:ListItem>Lod</asp:ListItem>
<asp:ListItem>Netanya</asp:ListItem>
<asp:ListItem>Hadera</asp:ListItem>
<asp:ListItem>Ashdod</asp:ListItem>
</asp:DropDownList>
<asp:button Text="Submit" OnClick=" SubmitBtn_Click " runat="server"
ID="Button1"/>
<p> Selected City: <asp:label text='<%# CityList.SelectedItem.Text %>'
runat="server" ID="Label1"/> </p>
</form></body></html>
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Output
Rather than explictly get
the variable from the
“CityList" ' and then
manipulate a label control
a Page.DataBind call is
performed.
This evaluates any <%#
%> expressions within the
page, including -
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DataBinding with a DataView
A DataView is a great class for presenting data to the user in a
more user-friendly format.
A DataView represents a databindable, customized view of a
DataTable.
The DataView and DataTable classes are defined in the
System.Data namespace.
A DataTable represents one table of in-memory data.
Data columns should be defined and added to DataTable dt
(dt.Columns.Add ) and later data rows should be added
(dt.Rows.Add).
To view a DataTable you need to use a DataView or a DataSet
class.
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Example
<%@ Import namespace="System.Data" %>
<html><head><script language="C#" runat="server">
void Page_Load(Object sender, EventArgs e )
{ if (!Page.IsPostBack) {
DataTable dt = new DataTable();
DataRow dr;
dt.Columns.Add(new DataColumn("IntegerValue", typeof(Int32)));
dt.Columns.Add(new DataColumn("StringValue", typeof(string)));
dt.Columns.Add(new DataColumn("DateTimeMsec", typeof(Int32)));
for (int i = 1; i <= 5; i++)
{
dr = dt.NewRow();
dr[0] = i; dr[1] = "Item " + i.ToString();
dr[2] = DateTime.Now.Millisecond;
dt.Rows.Add(dr);
}
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Example
dgr.DataSource = new DataView(dt);
dgr.DataBind();
}
}
</script>
</head><body>
<h3><font face="Verdana">Databinding to a DataView</font></h3>
<form runat=server ID="f">
<asp:DataGrid id="dgr" runat="server"
BorderColor="black"
BorderWidth="1"
GridLines="Both"
CellPadding="3"
CellSpacing="0"
HeaderStyle-BackColor="#aaaadd“ />
</form>
</body></html>
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Output
•DataGrid is a data bound list control that displays the
items from some data source in a table.
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Complex Data Binding
A complex data binding binds a list control (ListBox,
DropDownList) or iterative control (Repeater) to one or more
than one data element
typically more than one record in a database or to more than one of any
other type of bindable data elements.
Records of data usually retrieved from some database.
The ASP.NET framework includes the ADO.NET data access
technology for working with databases and other OLE DB data
sources.
ADO is ActiveX Data Object.
ADO.NET is a set of classes to access and work with databases.
ADO.NET is an evolution of the ADO data access model of Microsoft.
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Steps of data connection
and data manipulations
3 steps should be done to retrieve some data from DB
1.
A connection object created to represent a physical
connection to some data store (an SQL Server or an
DB
XML file).
2.
A command object created to represent a directive
Connection
to retrieve from (select) or manipulate (insert,
update, delete) the data store.
Command
3.
A dataset object created to represent the actual data.
DataSet
Note that DataSets are always disconnected from
their source connection and data model and can be
modified independently.
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Data Providers
In ADO.NET different namespaces and classes are
created to work with different data providers:
System.Data.SqlClient – Microsoft SQL Server 7.0 or
higher
System.Data.OleDb – OLE DB provider, such as
Microsoft Access
System.Data.OracleClient – Oracle Database server.
In our course you will work with SQL Server using
System.Data.SqlClient namespace.
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System.Data.SqlClient
System.Data.SqlClient
namespace includes 3
classes to perform data
connection and data
manipulation:
SqlConnection
SqlCommand
SqlDataReader
Database
SqlConnection
SqlCommand
SqlDataReader
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Opening a connection
To work with SQL Server the following directive
should be added to ASP.Net pages:
<%@ Import Namespace="System.Data.SqlClient" %>
The first step is to open a database connection.
SqlConnection class is used to establish a
connection to SQL Server database.
SqlConnection con;
con=new
SqlConnection("server=localhost;uid=sa;database=asp" );
con.open();
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SqlConnection
An SqlConnection class instance should be created (con=new
SqlConnection()).
It is initialized by passing a connection string to the
constructor of SqlConnection class.
The connection string should provide all necessary location
and authentication information to connect to SQL server.
server=localhost;uid=sa;pwd=secret;database=asp
where server=localhost (specifies a ServerName), uid=‘sa’ (specifies a
user sa=server admin), pwd (specifies a password if
required),Database=‘asp’ specifies the Database Name
Finally the connection is opened by calling an open() method
- con.open().
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SqlCommand
An SqlCommand class represents an SQL statement (query)
or a stored procedure.
SqlCommand myCommand = new SqlCommand("select * from Table",
con);
where a constructor specifies statement/query to perform and using
which database connection.
Later this object uses an ExecuteReader() method to
retrieve the result of the query.
The result may return non values (ExecuteNonQuery update) or to return a single value (ExecuteScalar - count)
or to return a DataReader(ExecuteReader).
If a record set is returned then it is stored in SqlDataReader
object.
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Partial Example
SqlConnection myConnection = new
SqlConnection("server=localhost;uid=sa;database=asp");
SqlCommand myCommand = new
SqlCommand( "UPDATE Table SET phone='(800) 555-5555'
WHERE au_id = '123-45-6789'", myConnection);
myCommand.Connection.Open();
myCommand.ExecuteNonQuery();
myCommand.Connection.Close();
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SqlDataReader
SqlDataReader class represents a stream of
database records returned from a SQL statement
(query) or a stored procedure.
SqlDataReader dr = myCommand.ExecuteReader();
It is a forward-only, read-only access to a set of
rows returned from a SQL server database.
Later some control should update it’s DataSource
property to this DataReader:
MyDataGrid.DataSource = dr;
MyDataGrid.DataBind();
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Final step
The final step do not forget
to close the DataReader: dr.Close();
to close the Connection: con.Close();
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Example
<%@ Page Language="C#"%>
<%@ Import Namespace="System.Data.SqlClient" %>
<script runat=server>
void Page_Load(Object sender , EventArgs e) {
SqlConnection con = new sqlConnection("Server=localhost;uid=sa;database=pubs");
con.Open();
SqlCommand cmd = new SqlCommand( "Select au_name From Authors", con );
SqlDataReader dtrAuthors = cmd.ExecuteReader();
Read method returns true if
while ( dtrAuthors.Read())
there is a next record to read
{ Response.Write( "<li>" );
Response.Write( dtrAuthors[ "au_name" ] ); }
dtrAuthors.Close();
Gets a value for the field called
con.Close();
au_name
}</script>
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Any Questions?
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