ASP.NET Guestbook Application

<%@ Page Language="C#"%>
<%@ Import Namespace="System.Data"%>
<%@ Import Namespace="System.Data.OleDb"%>

<script runat=server>

// #################################################################
// #
// # file:
// # 	guestbook/index.asp
// #
// # description:
// # 	guestbook application.
// #
// # author:
// # 	Uwe Keim, uk@zeta-software.de
// # 	zeta software GbR, Germany (www.zeta-software.de)
// #
// # history:
// # 	2002-01-26 Uwe Keim   converted for use with ASP.NET and C#.
// # 	2002-01-26 Uwe Keim   fixed some suggestions from CodeProject comments.
// # 	2000-01-13 Uwe Keim   fixed typo when deleting from the database.
// # 	2000-01-13 Uwe Keim   added count-down.
// # 	                      created resource strings.
// # 	1999-12-30 Uwe Keim   added admin mode.
// # 	                      added multiple pages and other stuff.
// # 	1999-11-24 Uwe Keim   file created.
// #
// #################################################################

// #################################################################
// configuration.

string DB_STR { get { return "Provider=Microsoft.Jet.OLEDB.4.0; Persist Security Info=False; Data Source=" + Server.MapPath("guestbook.mdb"); } }

// how many entries are being displayed on one page.
// normally you would specify here something between 20 and 50.
int HITS_PER_PAGE = 5;

// string resources, used by other parts of the page.
// used in order to separate code from content.
//-todo: add more.
string IDS_ANONYMOUS     = "Anonymous";
string IDS_FIELDSMISSING = "Not all required fields were filled out. Entry was not created.";
string IDS_ERRORINSERT   = "Error inserting entry.";
string IDS_ERRORDELETE   = "Error deleting entry.";
string IDS_MAIL          = "Send e-mail to";
string IDS_ERROR         = "Error occured.";

// #################################################################

</script>

<%
// #################################################################
// #################################################################
// #################################################################
// #################################################################
// "main function" and html code.

// set the global variable Mode.
Mode = Request["mode"]==null?MODE_NORMAL:Convert.ToInt32(Request["mode"]);

// new entry.
if ( HasMode(MODE_INSERT) )
{
	try
	{
		InsertEntry();
	}
	catch ( OleDbException e )
	{
		Response.Redirect( ErrorUrl(IDS_ERRORINSERT + " : " + e.Message), true );
		return;
	}
	catch ( Exception e )
	{
		Response.Redirect( ErrorUrl(IDS_FIELDSMISSING), true );
		return;
	}

	Response.Redirect( NormalUrl(), true );
	return;
}

// delete entry.
if ( HasMode(MODE_DELETE) )
{
	try
	{
		DeleteEntry();
	}
	catch ( Exception e )
	{
		Response.Redirect( ErrorUrl(IDS_ERRORDELETE + " : " + e.Message), true );
		return;
	}

	Response.Redirect( NormalUrl(), true );
	return;
}

// #################################################################

// query table and count the total number of entries.
DataTable Table = Execute( "SELECT * FROM Guestbook ORDER BY [Date] DESC" );

int sum_cnt = Table.Rows.Count;

// #################################################################
// calculate: pages, start, end, etc.

int cur_page;
if ( Request["pg"]==null )
	cur_page = 0;
else
	cur_page = Convert.ToInt32(Request["pg"]);

//int total_pages = sum_cnt/HITS_PER_PAGE;
int total_pages = sum_cnt/HITS_PER_PAGE;
if ( sum_cnt%HITS_PER_PAGE>0 && sum_cnt>HITS_PER_PAGE )
	total_pages++;

if ( total_pages<=0 ) 
	total_pages=1;

// the # of the displayed hits.
int hit_display_start = 1+cur_page*HITS_PER_PAGE;
int hit_display_end   = hit_display_start+Math.Min(sum_cnt,HITS_PER_PAGE)-1;
if ( hit_display_end>sum_cnt ) hit_display_end=sum_cnt;

// ---------------------------------
// the numbers must be displayed descending.

int cntdwn_start = sum_cnt-hit_display_start+1;
int cntdwn_end   = sum_cnt-hit_display_end+1;

// #################################################################
// navigation flags.

// whether there exists a previous or a next page.
bool can_prev_page       = cur_page>0;
bool can_next_page       = cur_page<total_pages-1;
bool can_prevornext_page = can_prev_page || can_next_page;

// ---------------------------------

// whether there exists a first and a last page.
bool can_first_page = can_prevornext_page && cur_page>0;
bool can_last_page  = can_prevornext_page && cur_page<total_pages-1;

// #################################################################

// "navigate" to start-recordset.
int table_index = hit_display_start-1;

// end of the pure asp-part.
// #################################################################
// #################################################################
// #################################################################
%>

<%// here starts the mixed html/asp part %>

<%// #################################################################%>
<%// #################################################################%>
<%// #################################################################%>
<%// #################################################################%>
<%// write error.%>

<% if ( HasMode(MODE_ERROR) ) { %>
	<p><font color="#FF0000"><b><%=IDS_ERROR + " : " + Request["error"]%></b></font><p>
<% } %>

<%// #################################################################%>
<%// link to insert. %>
<%// since the insert formular is at the bottom of the page, %>
<%// the user could not find it. therefore the link at the to. %>

<p><a href="#insert">Create new entry</a></p>

<%// #################################################################%>
<%// diplay information %>

<p><b><%=sum_cnt%></b> Entries found. 
	Page <b><%=cur_page+1%></b> of <b><%=total_pages%></b>, 
	entries <b><%=cntdwn_start%></b> to <b><%=cntdwn_end%></b>.</p>

<%// display top navigation buttons %>
<p> 
	<% if ( can_first_page ) { %><a href="<%=NaviUrl(0)            %>">First page</a><br>   <%}%>
    <% if ( can_prev_page  ) { %><a href="<%=NaviUrl(cur_page-1)   %>">Previous page</a><br><%}%>
	<% if ( can_next_page  ) { %><a href="<%=NaviUrl(cur_page+1)   %>">Next page</a><br>    <%}%>
	<% if ( can_last_page  ) { %><a href="<%=NaviUrl(total_pages-1)%>">Last page</a><br>    <%}%></p>

<p>
	<%
	// display discrete pages to jump directly to.
	for ( int i=1; i<total_pages; ++i )
	{
	%>

		<a href="<%=NaviUrl(i-1)%>">Page <%=i%></a>&nbsp

	<%
	}
	%>
</p>

<%
// #################################################################
// output all entries.

int cntdwn = cntdwn_start;

int cnt = 0;
while ( table_index<Table.Rows.Count && cnt<HITS_PER_PAGE )
{
	cnt++;

	DataRow row = Table.Rows[table_index];

	bool e = row["EMail"]!=null;
%>

	<%// one guestbook entry %>
	<hr size="1" color="#C0C0C0">

	<p><b><%=cntdwn%>.</b>&nbsp;<%if ( e ) {%><a title="<%=IDS_MAIL +" "+ row["EMail"]%>"
		href="mailto:<%=row["EMail"]%>"><%}%><%=row["Name"]%><%if ( e ) {%></a><%}%>, 
		<%=row["Date"]%>
		<%if ( HasMode(MODE_ADMIN) ) {%>&nbsp;<a href="<%=DeleteUrl(Convert.ToInt32(row["No"]))%>">Delete entry</a><%}%>
		</p>

	<p><%=FmtText(Convert.ToString(row["Text"]))%></p>
	<%//---------------------%>

<%
	cntdwn--;
	table_index++;
}
%>

<%// #################################################################%>
<%// separator line. %>

<p><br><hr size="1" color="#C0C0C0"><br></p>

<%// #################################################################%>
<%// output the entry-form. %>

<p><a name="insert"></a><b>Create new entry</b></p>

<p>Here you can create a new entry to the guestbook.</p>

<p>
	<form action="<%=InsertUrl()%>" method="post">
		Name:<br>
		<input type="text" name="gb_name" size="40"><br>

		<br>E-Mail:<br>
		<input type="text" name="gb_email" size="40"><br>

		<br>Text:<br>
		<textarea rows="10" name="gb_text" cols="40"></textarea><br>

		<br><input type="submit" value="Insert" name="gb_submit"><br>

		<input type="hidden" name="insert" value="true">
	</form>
</p>

<p>In your text, you can use the following HTML-tags: &lt;u&gt; &lt;i&gt;
&lt;b&gt; &lt;em&gt; (in lower-case)</p>

<%// #################################################################%>
<%// #################################################################%>
<%// #################################################################%>
<%// #################################################################%>
<%// here come the functions and constants.%>

<script runat="server">

// #################################################################
// global constants/variables.

// there is a global mode for the guestbook.
// depending on that mode, this page behaves different.
// you therefore don//t need different pages do to things like
// e.g. inserting or deleting.

// supported modes.
int MODE_NORMAL = 1;		// normal viewing of the guestbook.
int MODE_ERROR  = 2;		// an error occured and is displayed.
int MODE_INSERT = 4;		// inserting of a item into the guestbook.
int MODE_DELETE = 8;		// deleting of an item of the guestbook.
int MODE_ADMIN  = 16;		// administration-mode: allows deletion of articles.

// read mode. default to normal.
int Mode;

// #################################################################
// general helper functions.

// replaces \n with <br>.
string FmtMl( string in_str )
{
	if ( in_str==null || in_str.Length==0 )
		return "";

	string str;
	str = in_str.Replace( "\r\n", "\n" );
	str = str   .Replace( "\r"  , "\n" );
	str = str   .Replace( "\n"  , "<br>" );

	return str;
}

// allow several html codes, but not all.
string FmtText( string txt )
{
	// first encode all.
	txt = Server.HtmlEncode(txt);

	// then decode the allowed tags.
	txt = txt.Replace( Server.HtmlEncode("<u>"), "<u>" );
	txt = txt.Replace( Server.HtmlEncode("</u>"), "</u>" );

	txt = txt.Replace( Server.HtmlEncode("<i>"), "<i>" );
	txt = txt.Replace( Server.HtmlEncode("</i>"), "</i>" );

	txt = txt.Replace( Server.HtmlEncode("<b>"), "<b>" );
	txt = txt.Replace( Server.HtmlEncode("</b>"), "</b>" );

	txt = txt.Replace( Server.HtmlEncode("<em>"), "<em>" );
	txt = txt.Replace( Server.HtmlEncode("</em>"), "</em>" );

	return FmtMl(txt);
}

// #################################################################
// url functions.

// these functions should be used whenever you need a <a href="...">
// tag. instead of specifying an asp page and adding some cryptic
// parameters, you call one of these functions.
// with this approach, you can centralize the url-parameters
// in one place.

// the url of this page.
// automatically adds admin mode if currently active.
string MyselfUrl( int mode_ )
{
	if ( (Mode & MODE_ADMIN)!=0 )
		mode_ = mode_ | MODE_ADMIN;

	return Request.ServerVariables["SCRIPT_NAME"] + "?mode=" + mode_;
}

// url for viewing the guestbook in normal mode.
string NormalUrl()
{
	return MyselfUrl(MODE_NORMAL);
}

// url for displaying an error.
string ErrorUrl( string error_text )
{
	return MyselfUrl(MODE_ERROR) + "&error=" + Server.UrlEncode(error_text);
}

// url for inserting a new entry to the guestbook.
string InsertUrl()
{
	return MyselfUrl(MODE_INSERT);
}

// url for deleting an entry from the guestbook.
string DeleteUrl( int id )
{
	return MyselfUrl(MODE_DELETE) + "&id=" + Server.UrlEncode(id.ToString());
}

string NaviUrl( int page )
{
	return MyselfUrl(MODE_NORMAL) + "&pg=" + page;
}

// #################################################################
// special helper functions.

// insert a new entry to the guestbook.
void InsertEntry()
{
	// read parameters.
	string name  = Request["gb_name"];
	string email = Request["gb_email"];
	string text  = Request["gb_text"];

	// check parameters.
	if ( name==null ) name = IDS_ANONYMOUS;
	if ( text==null ) throw new Exception( "Text to insert not specified" );

	// --
	// full code to write the new entry to the database.

	OleDbConnection     conn = new OleDbConnection( DB_STR );
	OleDbDataAdapter    da   = new OleDbDataAdapter( "SELECT * FROM Guestbook", conn );
	OleDbCommandBuilder cb   = new OleDbCommandBuilder( da );

	// this is important, since the database contains reserved SQL keywords (Date and Text).
	cb.QuotePrefix = "[";
	cb.QuoteSuffix = "]";

	DataSet ds = new DataSet();
	da.Fill( ds );

	DataTable table = ds.Tables[0];

	DataRow row = table.NewRow();
	row["Date"]  = DateTime.Now;
	row["Name"]  = name;
	row["EMail"] = email;
	row["Text"]  = text;
	table.Rows.Add( row );

	da.Update( ds );

	conn.Close();
}

// delete an entry from the guestbook.
void DeleteEntry()
{
	// check parameters.
	if ( Request["id"]==null )
		throw new Exception( "ID to delete no specified" );
	
	// read parameters.
	int id = Convert.ToInt32(Request["id"]);

	// actually delete the entry.
	ExecuteNonQuery( "DELETE FROM Guestbook WHERE [No]=" + id );
}

// check, whether a mode is currently active.
bool HasMode( int mode_chk )
{
	return (Mode & mode_chk)!=0;
}

// #################################################################
// helper routines for the database.

// single-line-shortcut for executing a query that returns NO results.
void ExecuteNonQuery( string sql )
{
	OleDbConnection	conn = new OleDbConnection( DB_STR );
	conn.Open();
	OleDbCommand    cmd  = new OleDbCommand( sql, conn );
	cmd.ExecuteNonQuery();

	conn.Close();
}

// opens the recordset with the query.
DataTable Execute( string sql )
{
	OleDbConnection	 conn = new OleDbConnection( DB_STR );
	OleDbCommand     cmd  = new OleDbCommand( sql, conn );

	OleDbDataAdapter da   = new OleDbDataAdapter();
	da.SelectCommand = cmd;

	DataSet ds = new DataSet();
	da.Fill( ds );

	conn.Close();

	return ds.Tables[0];
}

// #################################################################

</script>