Friday, May 7, 2010
How to install software on a netbook from a CD?
Not exactly a software development tip but a very useful one: If you have a netbook, you probably don't have a CD drive. How can you install a software with a CD installation? When I searched the web for a solution I found all kinds of suggestions like buying a portable CD with USB drive (the whole idea was buying a cheap computer, not having to start purchasing accessories), or use special applications for moving the content of the CD to a portable disk. Then my partner came up with an excellent and simple idea: after connection the netbook to the network, put the CD in one of the other computers on the same network, and share the CD drive. Then I could access the CD from the network and install all I needed.
Wednesday, April 28, 2010
Error: "The type or namespace name 'Linq' does not exist in the namespace 'System.Data' (are you missing an assembly reference?)"
I got this error when I uploaded to the web server a new version of my site using LINQ. Everything worked on my local machine and on a local web server so I knew my code was right.
At first I thought the web server does not support LINQ and I asked the support group of the web server to enable LINQ for my site, buy they insisted that ASP.NET 3.5 that support LINQ is already installed and insisted that the problem is in my code.
Eventually I remembered that I didn't update the web.config file, since it is different for my local machine and for the web server, and I didn't want to overwrite the changes. When comparing the two files, I found out that this line is missing on the web.config file on the web server:
<add assembly="System.Data.Linq, Version=3.5.0.0, Culture=neutral, PublicKeyToken=..."/>
After adding this line, I didn't see this message on the web server any more.
At first I thought the web server does not support LINQ and I asked the support group of the web server to enable LINQ for my site, buy they insisted that ASP.NET 3.5 that support LINQ is already installed and insisted that the problem is in my code.
Eventually I remembered that I didn't update the web.config file, since it is different for my local machine and for the web server, and I didn't want to overwrite the changes. When comparing the two files, I found out that this line is missing on the web.config file on the web server:
<add assembly="System.Data.Linq, Version=3.5.0.0, Culture=neutral, PublicKeyToken=..."/>
After adding this line, I didn't see this message on the web server any more.
Monday, April 26, 2010
Why don't my dynamic controls work?!
I had a bug that drove me crazy: in one of my ASP.NET pages, none of the dynamic control worked, meaning when I clicked a button, nothing happened, and the callback function wasn't called.
I suspected AJAX, but even after I removed all traces of AJAX in the page, the controls still didn't work.
I started removing code from the page, until all the code-behind file was almost empty, to no avail.
So I went to the .aspx file, and started removing controls from the page.
Until I removed one control, and suddenly my dynamic controls started working fine.
The control that caused all the problem was a required field validation.
My error was that I forgot to assign a ValidationGroup property to the validator. Since it didn't have any validation group, it got activated every time any control was clicked on the page, and caused the action to fail using client call, before any code got to the server code-behind of the page.
I hope this will save some time for another programmer with similar problem.
I suspected AJAX, but even after I removed all traces of AJAX in the page, the controls still didn't work.
I started removing code from the page, until all the code-behind file was almost empty, to no avail.
So I went to the .aspx file, and started removing controls from the page.
Until I removed one control, and suddenly my dynamic controls started working fine.
The control that caused all the problem was a required field validation.
My error was that I forgot to assign a ValidationGroup property to the validator. Since it didn't have any validation group, it got activated every time any control was clicked on the page, and caused the action to fail using client call, before any code got to the server code-behind of the page.
I hope this will save some time for another programmer with similar problem.
Friday, May 1, 2009
Searching for articles by tag and other criteria
Here is an expansion of the problem from the last post. Now I have many articles, each has a title, an author, a list of tags, and other parameters. Let's say for simplicity that all the data is in one table - Articles, with the fields: id, title, author, and the tags are in a separate table called Tags with the fields ArticleID and Name.
Now I am looking for a single SQL command to search for articles with some text in their title, some text in their author, and some text in one of their tags.
Since there could be more then one tag for each article, it cannot be done by a simple query on the articles table.
To do that, I need to use subquery in the WHERE clause.
Here is the solution:
SELECT Atricles.ID, Articles.Title, Articles.Author
FROM Articles
WHERE Article.Title LIKE '%someText1%'
AND Article.Author LIKE '%someText2%'
AND (0 < (SELECT COUNT(*) FROM Tags
WHERE Tags.ArticleID = Articles.ID
AND Tags.NAME LIKE '%someText3%')
Now I am looking for a single SQL command to search for articles with some text in their title, some text in their author, and some text in one of their tags.
Since there could be more then one tag for each article, it cannot be done by a simple query on the articles table.
To do that, I need to use subquery in the WHERE clause.
Here is the solution:
SELECT Atricles.ID, Articles.Title, Articles.Author
FROM Articles
WHERE Article.Title LIKE '%someText1%'
AND Article.Author LIKE '%someText2%'
AND (0 < (SELECT COUNT(*) FROM Tags
WHERE Tags.ArticleID = Articles.ID
AND Tags.NAME LIKE '%someText3%')
Saturday, March 14, 2009
Find an article with a list of tags
Let's say I have a web site with articles, and each article can have one or more tags, just like the blog posts in this web site (where they are called "labels").
I save all of the article's tags in a table, called ArticleTags, that have two columns: ArticleId and TagId.
Now let's say I have a list of tags - ASP.NET, SQL and WEB, for example, with IDs 1,2,3.
I want to find all of the articles that have all 3 tags.
If I try the simple query
SELECT ArticleID FROM ArticleTags WHERE TagId in (1,2,3)
I will get all the articles with either tag 1 or tag 2 or tag 3 - not the articles with all three of them.
When I looked for solutions on the web, I was surprised to find that many implemented this by saving all the tags as one long text field of the articles = "ASP.NET,SQL,WEB" - and used "LIKE" in the query. It is inefficient, because of the use of "like", and because the search is on the tag text itself and not on the tag ID, and also limits the number of tags to the capacity of one field, and I also want to save the text in a separate table, for localizations and other uses.
I finally got the following solution that gives me exactly what I was looking for:
SELECT ArticleID
FROM ArticleTags
WHERE (TagId IN (1, 2, 3))
GROUP BY ArticleID
HAVING (COUNT(*) = 3)
I am using the GROUP option to group all the same ArticleID together, and then count them. If their count is exactly the number of Tag IDs I am looking for, it means that this article has all the tags in my list. This condition has to be in the HAVING part of the query and not in the WHERE clause because it uses an aggregation field.
I save all of the article's tags in a table, called ArticleTags, that have two columns: ArticleId and TagId.
Now let's say I have a list of tags - ASP.NET, SQL and WEB, for example, with IDs 1,2,3.
I want to find all of the articles that have all 3 tags.
If I try the simple query
SELECT ArticleID FROM ArticleTags WHERE TagId in (1,2,3)
I will get all the articles with either tag 1 or tag 2 or tag 3 - not the articles with all three of them.
When I looked for solutions on the web, I was surprised to find that many implemented this by saving all the tags as one long text field of the articles = "ASP.NET,SQL,WEB" - and used "LIKE" in the query. It is inefficient, because of the use of "like", and because the search is on the tag text itself and not on the tag ID, and also limits the number of tags to the capacity of one field, and I also want to save the text in a separate table, for localizations and other uses.
I finally got the following solution that gives me exactly what I was looking for:
SELECT ArticleID
FROM ArticleTags
WHERE (TagId IN (1, 2, 3))
GROUP BY ArticleID
HAVING (COUNT(*) = 3)
I am using the GROUP option to group all the same ArticleID together, and then count them. If their count is exactly the number of Tag IDs I am looking for, it means that this article has all the tags in my list. This condition has to be in the HAVING part of the query and not in the WHERE clause because it uses an aggregation field.
Tuesday, March 10, 2009
Validating CheckBoxList Control
ASP.NET provides the validation controls that enables checking if the input is valid before starting to process in on the server and thus save time for the user. These controls are very easy to use. However when I tried to user a required field validator for a CheckboxList control, to make sure that the user selected at least one item, I got an exception, saying that the control to validate is invalid. It turned out that the validation does not work for CheckboxList.
I found the following article about it:
http://aspnet.4guysfromrolla.com/articles/092006-1.aspx
It claims that there are 3 possible solutions: implement the validation not using the validation controls, use custom validation controls and write the validation methods, or create a custom control that does the validation the same way as the validation controls provided by the ASP.NET.
Since the third option is out of my scope for this project, I chose the second option, using the custom validation control.
However, when I created a custom validation control and set the control to validate as my checkbox list, I got the same exception again - a checkbox list cannot be the control to validate, even for a custom validation control.
So I decided to use a dummy control as the control to validate. The problem was that I needed a way to know which control to validate. These checkbox lists are created dynamically at runtime.
This is what I did: I created a dummy textbox and put the ID of the checkboxlist as the value inside the text box. I sent the textbox as the control to validate, and then got the ID of my "real" control to validate from the value that was sent to the validation function, and used it to find my checkbox list and perform the validation checks.
But of course I didn't want the user to see the dummy text box. So I set its "Visibility" to false.
When I did that, the validation method was never called. So it seems like the ASP.NET does not perform validation for a control whose visibility is false.
The solution was to hide it by setting its "display" attribute to "none".
One last problem I had when developing this solution: When I only had the server-side validation method, things didn't work well, I could not see the error message and the operation wasn't stopped. After I added the javascript client-side validation function, everything worked just fine.
Here is the code:
Creating the dummy text box and the custom validation control:
// add dummy text box just for passing to validation function
TextBox txtDummy = new TextBox();
txtDummy.ID = "txt_checkbox_" ID.ToString();
txtDummy.Text = chk.ID.ToString(); // chk is the checkboxlist to validate
txtDummy.Attributes.CssStyle.Add(HtmlTextWriterStyle.Display, "none");
Panel1.Controls.Add(txtDummy);
// add custom validation control
CustomValidator valCheck = new CustomValidator();
valCheck.ControlToValidate = txtDummy.ID;
valCheck.ErrorMessage = "You must select at least one value!";
valCheck.ServerValidate = new ServerValidateEventHandler(ValidateCheckbox);
valCheck.ClientValidationFunction = "CheckVal";
Panel1.Controls.Add(valCheck);
Server side validation method:
void ValidateCheckbox(Object source, ServerValidateEventArgs args)
{
// get the checkbox list
CheckBoxList chk = Panel1.FindControl(args.Value) as CheckBoxList;
// check if at least one option is selected
if (chk.SelectedIndex < 0)
args.IsValid = false;
else
args.IsValid = true;
}
Client side validation method:
function CheckVal(sender, args)
{
var checkID = args.Value;
var checDP = document.getElementById(checkID);
var selectedItemCount = 0;
var liIndex = 0;
var currentListItem = document.getElementById(checDP.id + '_' + liIndex.toString());
while (currentListItem != null)
{
if (currentListItem.checked)
selectedItemCount++;
liIndex++;
currentListItem = document.getElementById(checDP.id + '_' + liIndex.toString());
}
if (selectedItemCount == 0)
{
args.IsValid = false;
return;
}
args.IsValid = true;
}
I found the following article about it:
http://aspnet.4guysfromrolla.com/articles/092006-1.aspx
It claims that there are 3 possible solutions: implement the validation not using the validation controls, use custom validation controls and write the validation methods, or create a custom control that does the validation the same way as the validation controls provided by the ASP.NET.
Since the third option is out of my scope for this project, I chose the second option, using the custom validation control.
However, when I created a custom validation control and set the control to validate as my checkbox list, I got the same exception again - a checkbox list cannot be the control to validate, even for a custom validation control.
So I decided to use a dummy control as the control to validate. The problem was that I needed a way to know which control to validate. These checkbox lists are created dynamically at runtime.
This is what I did: I created a dummy textbox and put the ID of the checkboxlist as the value inside the text box. I sent the textbox as the control to validate, and then got the ID of my "real" control to validate from the value that was sent to the validation function, and used it to find my checkbox list and perform the validation checks.
But of course I didn't want the user to see the dummy text box. So I set its "Visibility" to false.
When I did that, the validation method was never called. So it seems like the ASP.NET does not perform validation for a control whose visibility is false.
The solution was to hide it by setting its "display" attribute to "none".
One last problem I had when developing this solution: When I only had the server-side validation method, things didn't work well, I could not see the error message and the operation wasn't stopped. After I added the javascript client-side validation function, everything worked just fine.
Here is the code:
Creating the dummy text box and the custom validation control:
// add dummy text box just for passing to validation function
TextBox txtDummy = new TextBox();
txtDummy.ID = "txt_checkbox_" ID.ToString();
txtDummy.Text = chk.ID.ToString(); // chk is the checkboxlist to validate
txtDummy.Attributes.CssStyle.Add(HtmlTextWriterStyle.Display, "none");
Panel1.Controls.Add(txtDummy);
// add custom validation control
CustomValidator valCheck = new CustomValidator();
valCheck.ControlToValidate = txtDummy.ID;
valCheck.ErrorMessage = "You must select at least one value!";
valCheck.ServerValidate = new ServerValidateEventHandler(ValidateCheckbox);
valCheck.ClientValidationFunction = "CheckVal";
Panel1.Controls.Add(valCheck);
Server side validation method:
void ValidateCheckbox(Object source, ServerValidateEventArgs args)
{
// get the checkbox list
CheckBoxList chk = Panel1.FindControl(args.Value) as CheckBoxList;
// check if at least one option is selected
if (chk.SelectedIndex < 0)
args.IsValid = false;
else
args.IsValid = true;
}
Client side validation method:
function CheckVal(sender, args)
{
var checkID = args.Value;
var checDP = document.getElementById(checkID);
var selectedItemCount = 0;
var liIndex = 0;
var currentListItem = document.getElementById(checDP.id + '_' + liIndex.toString());
while (currentListItem != null)
{
if (currentListItem.checked)
selectedItemCount++;
liIndex++;
currentListItem = document.getElementById(checDP.id + '_' + liIndex.toString());
}
if (selectedItemCount == 0)
{
args.IsValid = false;
return;
}
args.IsValid = true;
}
Tuesday, March 3, 2009
ERROR: "Microsoft JScript runtime error: ASP.NET Ajax client-side framework failed to load" When using AJAX
I added some AJAX functionality to an existing AST.NET website. It was my first experience with AJAX.NET.
I started with a simple tutorial, built a new small web site with AJAX, and everything worked just fine.
Then I tried to implement it to my existing website.
First I had to upgrade the website from .NET 2.0 to .NET 3.5, to enable the java controls. I am working with Visual Studio 2008, but I set the website to 2.0, so that I could work with it on my laptop, where I had the previous version of visual studio.
After upgrading the website to version 3.5 of .NET, I added a very simple AJAX control: I wrapped an existing button with UpdatePanel, to prevent page refresh when the button is clicked.
When I ran the website, I got the error message:
Microsoft JScript runtime error: ASP.NET Ajax client-side framework failed to load.
I started searching the web for this error. Many programmers met this error message, and it seemed like the suggested solutions were of two types:
1. Checking if AJAX extension was properly installed - which is irrelevant to me, because I work with Visual Studio 2008 where AJAX is built-in, and also the simple AJAX website worked fine.
2. Set the web server - the IIS - to recognize *.axd files. Again it could not apply to me because I was running everything locally, through Visual Studio, and I don't even have IIS installed on my machine.
I went on searching and researching the problem, and found on some forum some semi-cryptic comment about wrong HttpHandlers on the Web.config files.
When I looked at my Web.config file, I could not find any HttpHandler or something like that.
It turned out that a whole section was supposed to be added to the Web.config file when I upgraded the website from .NET 2.0 to .NET 3.5, and for some reason this section was not there. Seems like something went wrong in the upgrade process. When I did the upgrade again, I could see the section about the handlers in the Web.config file, and this time everything worked just fine. This is part of what was missing in the Web.config that is relevant:
<modules>
<remove name="ScriptModule"/>
<add name="ScriptModule" preCondition="managedHandler" .../></modules>
<handlers>
<remove name="WebServiceHandlerFactory-Integrated"/>
<remove name="ScriptHandlerFactory"/>
<remove name="ScriptHandlerFactoryAppServices"/>
<remove name="ScriptResource"/>
<add name="ScriptHandlerFactory" verb="*" path="*.asmx" preCondition="integratedMode..."/>
<add name="ScriptHandlerFactoryAppServices" verb="*" path="*_AppService.axd" .../>
<add name="ScriptResource" verb="GET,HEAD" path="ScriptResource.axd" preCondition="integratedMode" .../>
</handlers>
Seems like it has something to do with recognizing the script files generated for the client side AJAX implementation.
Anyway, after fixing the Web.config file, the error code disappeared and AJAX works just fine.
I started with a simple tutorial, built a new small web site with AJAX, and everything worked just fine.
Then I tried to implement it to my existing website.
First I had to upgrade the website from .NET 2.0 to .NET 3.5, to enable the java controls. I am working with Visual Studio 2008, but I set the website to 2.0, so that I could work with it on my laptop, where I had the previous version of visual studio.
After upgrading the website to version 3.5 of .NET, I added a very simple AJAX control: I wrapped an existing button with UpdatePanel, to prevent page refresh when the button is clicked.
When I ran the website, I got the error message:
Microsoft JScript runtime error: ASP.NET Ajax client-side framework failed to load.
I started searching the web for this error. Many programmers met this error message, and it seemed like the suggested solutions were of two types:
1. Checking if AJAX extension was properly installed - which is irrelevant to me, because I work with Visual Studio 2008 where AJAX is built-in, and also the simple AJAX website worked fine.
2. Set the web server - the IIS - to recognize *.axd files. Again it could not apply to me because I was running everything locally, through Visual Studio, and I don't even have IIS installed on my machine.
I went on searching and researching the problem, and found on some forum some semi-cryptic comment about wrong HttpHandlers on the Web.config files.
When I looked at my Web.config file, I could not find any HttpHandler or something like that.
It turned out that a whole section was supposed to be added to the Web.config file when I upgraded the website from .NET 2.0 to .NET 3.5, and for some reason this section was not there. Seems like something went wrong in the upgrade process. When I did the upgrade again, I could see the section about the handlers in the Web.config file, and this time everything worked just fine. This is part of what was missing in the Web.config that is relevant:
<modules>
<remove name="ScriptModule"/>
<add name="ScriptModule" preCondition="managedHandler" .../></modules>
<handlers>
<remove name="WebServiceHandlerFactory-Integrated"/>
<remove name="ScriptHandlerFactory"/>
<remove name="ScriptHandlerFactoryAppServices"/>
<remove name="ScriptResource"/>
<add name="ScriptHandlerFactory" verb="*" path="*.asmx" preCondition="integratedMode..."/>
<add name="ScriptHandlerFactoryAppServices" verb="*" path="*_AppService.axd" .../>
<add name="ScriptResource" verb="GET,HEAD" path="ScriptResource.axd" preCondition="integratedMode" .../>
</handlers>
Seems like it has something to do with recognizing the script files generated for the client side AJAX implementation.
Anyway, after fixing the Web.config file, the error code disappeared and AJAX works just fine.
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