Mac Software Development

I have have done my software development mainly in Windows Platform, some in Unix long time ago. I have got an iMac in March this year. Since then I spend a lot of my time using it at home. I really enjoy it. Recently I have installed XCode on my Mac and watched training videos about iPhone Application Development API kit.

It is very interesting to learn Objective-C and Cocoa framework even they are very different from .Net languages and framework. iMac computer is very easy to use and very stable. From what I have seen from Apple's training materials, the Objective-C and Cocoa are also very straight forward in syntax. Objective-C for Mac applications uses MVC pattern. That's the one I have seen on Microsoft's P&P team as well. I think there are a lots similarities between both.

I'll spend some time to learn Mac application development. Maybe I'll get more and more involved in Mac software development. Enjoy the new adventure!

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Google Launches Chrome Web Browser Today

It is getting more crowded in the web browser war. I have IE that is a part of Windows, Firefox, an excellent open source browser with multi-tabs and add-ins, Safari for Mac, and others rarely used. Now Google enters the web browser competition with Chrome!

It is a positive thing for most end users for sure. I think Chrome will have some special offers for us. First, it is built based on IE but it is open source. Soon it will be available for Mac. That means that we could have alternative browser for IE in Mac with IE special features. Secondly, its infrastructure is sandbox so that each process has its own rights which mean more privacy. Another related benefit is that one process crashing would not affect others like tabs and mails.

I think the biggest thing why Google decides to have its own browser is that the current browsers have too many dependencies. Many of Google's products and great features are depending on browser and end user decisions. For example, Google released Google Gears which provides off-line browsing. That's a great feature for most end users. The browsing process would more smooth and faster. The real-time data can be updated by the back-end database store and processes when the Internet connection is available and there is need to fresh the data. However, it is an add-in. It will be up to the end user to install it. Without the installation, it would not work.

jQuery is another great feature for web browsing. It loads additional JavaScript libraries. There are already many jQuery add-ins or plug-ins available and Google shows great interest in it. However, many features will depend on end users to install them.

I guess that Chrome will install Google Gears and many other add-ins as components by default. This will make Chrome very unique and outstanding. Many advanced features will be available right away. That will shine Chrome for sure.

Welcome Chrome to the web browser world!

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jQuery

Today I read David Hayden's blog on jQuery. It is a quite interesting JavaScript library. I tried some tutorial examples and get some tastes on how to use and its initial power.

I downloaded the library jQuery-1.2.6.js source code. Then I created a test html file. I followed the instruction to save the js file in the same folder as the html file. Then I tried some example codes to hide a reference link <a...>, add a style class to the link, add a click event to the link, and some chained queries. Basically, this library provides API functions to manipulate DOM objects or elements, handle events, perform animation, and add Ajax to your web project. As David recommended, jQuary in Action is a good book for beginners.

I'll spend some time to try out and learn this great tool. Hopefully I can use this in my web projects.

Here is a training video program by a 12 years old child in google engEdu:



Here is very good reference to jQuery API libraries: Visual jQuery 1.1


50+ Amazing jQuery Examples. Unfortunately, some links are not available. However, some are really amazing web pages.

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Collection Filter Function

Let's continue the topic of my previous blog on .Net Generic and Value Data Type with an example of collection filter function for generic value data types. This function takes two collections, the first one as input collection and another one as filter collection. The returned collection will filter out all the items in the filter collection from the first collection. In this case, in order to filter items, the value data type makes sense when comparing equalities for all the items in a collection to an item. For reference data types, however, it is hard to tell equality or not, by reference or property members? You even can expect multiple-levels if some property members are reference types.

public IEnumerable<T> FilerCollections<T>(
  IEnumerable<T> list,
  IEnumerable<T> filterList)
  where T: struct
  {
  if ( list != null )
  {
    foreach (T item in list)
    {
      bool found = false;
      if (filterList != null)
      {
        foreach (T filterItem in filterList)
        {
          if (filterItem.Equals(item))
          {
            found = true;
            break;
          }
        }
      }
      if (!found)
      {
        yield return item;
      }
    }
  }
}

Here is the test program:

Test t = new Test();
IEnumerable<int> list;
List<int> list1 = new List<int>(new int [] {1, 2, 3, 4});
List<int> list2 = new List<int>(new int[] {3});
list = t.FilerCollections<int>(list1, list2);
if (list != null)
{
    foreach (int item in list)
    {
        Console.WriteLine("item: {0}", item);
    }
}
else
{
    Console.WriteLine("List is empty");
}

and the result screen:

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.Net Generics and Value Data Type

I use .Net Generics a lot. The great benefit is that you can make your codes reusable even you may use it only for one data type. You may extract the generic class or method to a library to a library for reuse. Secondly, it still keeps type safe or strong type integrity. Any attempts to use wrong type will be caught at compile time instead of run time.

The generics can be specified by where clause. In most cases I use generics for reference data types, i.e., classes. If you say a generic as class, that means the generics data type is a reference type. You can use new() to further indicate the class can be instantiated by the default constructor with no parameters. If you specify the class a specified class, that means any class which inherits from the class can be used for the generics class or method.

You cannot use more than one classes in where clause, however, you can use interfaces to specify that the generic class should implement some interfaces. Then in your generic class or method, you can safely call the implemented interfaces or methods.

How about value data types such as int, string or double as examples. You can use struct in the where clause. If you want to use the nullable value data types, you can simply use ? after the generic type, such as T?.

class Test
{
  public T GetValueOrDefault<T>(T? item) 
    where T: struct
  {
    return item.GetValueOrDefault();
  }
  public T? GetValue<T>(T? item) 
    where T: struct
  {
    if (item.HasValue)
    {
      return item.Value;
    }
    else
    {
      return null;
    }
  }
}

here are codes to call the methods:

Test t = new Test();
int? a = 2;
a = t.GetValueOrDefault<int>(a);
//t.GetValueOrDefault<Test>(t); //Error: t is not none-nullable data type
Console.WriteLine("GetValueOrDefault<int>(a) = {0}; GetValue<int>(a) = {1}", 
    t.GetValueOrDefault<int>(a), t.GetValue<int>(a));
a = null;
Console.WriteLine("GetValueOrDefault<int>(a) = {0}; GetValue<int>(a) = {1}", 
    t.GetValueOrDefault<int>(a), t.GetValue<int>(a));
Console.WriteLine("GetValueOrDefault<int>(a) = {0}; GetValue<int>(a) = {1}", 
    t.GetValueOrDefault<int>(3), t.GetValue<int>(3));

 

The result of the above codes in a console is:



Here is an interest posting on .Net Generics and a question about enum data type.

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SQL Nested SELECT Statement in FROM Clause

You can create a view by using SELECT statement. For example, a View called as AllEmployeeInfo by SQL statement: SELECT * FROM Employees. Employees is a table. That's quite simple. Then you many list all employee names hired after '2005-01-01' from the view:

SELECT FirstName, LastName
  FROM AllEmployeeInfo

Is there any way to use SQL SELECT statement as a subquery directly in FROM clause? For example:

SELECT FirstName, LastName
  FROM SELECT * FROM Employees

This does not work in Microsoft SQL 2005. However, if you name the subquery SELECT as an alias, you can do it. Here is the example:

SELECT FirstName, LastName
  FROM (SELECT * FROM Employees
          WHERE HireDate > '2005-01-01') AS Temp
-- or
SELECT FirstName, LastName
  FROM (SELECT * FROM Employees) AS Temp
  WHERE HireDate > '2005-01-01'

It looks like that SQL will create a temporary or dynamic view for the alias, then you could SELECT columns from there. Quite cool? I tried this in PL/SQL Oracle 9.0 but it does not work. Anyway, I like this quick way to get data. Sometimes you may need this kind of nested SELECTs so that you can filter data by several levels and avoid to create unnecessary views.

More on nested SQL queries, read this blog: Using a Subquery in a T-SQL statement.

Notes and Updates on this blog: Actually, the nested SELECT statement is available in Oracle or PL/SQL as well, but you don't need to AS in the statement. I got this correction from my StackOverFlow Q&A. Thanks for the correction!

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ASP.Net and Data Source Controls

In an ASP.Net page, many asp controls can be bound with a data source control, such as SqlDataSource and ObjectDataSource. I prefer to use ObjectDataSource than SqlDataSource. Here are my two main reasons.

First SqlDataSource includes a SQL statement in the control. If you change different data DB source from Microsoft SQL to Oracle DB, the SQL statement may be different. Therefore, you may have to make change in the UI aspx page or server side .Net class codes.

ObjectDataSource is binding data source from a a class's methods to get or update data. The class hides the way how data are retrieved or saved. I call it as business logic layer class (BLL). The class can be defined in another library assembly. This will make unit test much easier.

Second reason is that you don't have control how many times to call SqlDataSource to get data. For example, if you have a combo box in a GridView for product types and link it to a SqlDataSource to get product types. Each combo box will call the SqlDataSource to get product types when GridView is initialized. If there are tens or hundreds of rows in the GridView, there will be tens or hundreds call to database to get the same data. Even worse, in case of post-back calls, the GridView will be refreshed again. This may make the front UI very slow if the retrieving data process is slow.

In BLL class, you can easily cache data to avoid unnecessary calls to database. Simple define your data collection as a static List in the class. Only the first time when the page is initialized the static data member is populated with data from database. The subsequent calls will get data from the cache. You may need to define a reset method in the BLL class so that in the Page_Load event, if it is not post-back call, call this reset method to reset the static member to null. Then when the GridView is initialized, the data will be obtained from database for the first time.

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Using Query String Parameters in ASP.Net Page

You can use query string parameters in a URL request string to pass information into an aspx page. This is very common way to pass values from one page to another page. The URL query string is in the format like:

http://mypage.aspx?para1=value1¶2=value2...

I also use this mechanism to pass in additional data or flags to display some hidden values or to provide additional information from server side codes. For example, in a GridView control, normally we only display a UI table which are readable by clients, such as employee first name, last name and department. The employee ID, which is important information for server side updating, is normally a hidden column in the table.

As in this example, my codes handle some query parameters. One is "displayEmployeeID". If it is true, the employee ID then is visible:

http://mypage.aspx?para1=value1¶2=value2&displayEmployeeID=true

This parameter can be manually added the URL address text box (use & to separate parameters). If it is not available, the default value is false. Here are some codes in my aspx.cs page in the Page_Load() event:

bool display = false;
string sVal = HttpUtility.UrlDecode(Request.QueryString["displayEmployeeID"]);
if (string.IsNullOrEmpty(sVal) == false)
{
  if (!bool.TryParse(sVal, out display))
  {
    display = false;
  }
}
DataGridView.Columns[0].Visible = display;

I use the same way to display my business logic layer class's SQL string on my page so that it makes my debugging work very easy. I add a panel to the page in aspx:

<asp:Panel ID="panelDebug" runat="server" Visible="false" width="720px">
  <table width="100%"><tr align="left" ><td style="width: 110px" >
    <asp:Label ID="lblSQL" runat="server" Text="Create Object SQLs: " /></td><td>
    <asp:TextBox ID="txtSQL" runat="server" Wrap="true" Width="600px"></asp:TextBox>
    </td></tr><tr align="left"><td style="width: 25%">
    <asp:Label ID="lblUpdate" runat="server" Text="Updates: " ></asp:Label></td><td>
    <asp:TextBox ID="txtUpdate" runat="server" Width="600px" Wrap="true"></asp:TextBox>
    </td></tr>
  </table>
</asp:Panel>

Then in the event of Page_Load() and the place when my business class has retrieved data from a SQL DB:

panelDebug.Visible = GetDisplaySQL(); // method to get query parameter "displaySQL" value 
...
txtSQL.Text = bllObj.QuerySQLs; // udpate SQL by BLL class property QuerySQLs
...

Here the text box txtUpdate is as same as query SQL but for update SQL statements.

I call those query parameters as hidden parameters. They provide handy ways to get additional information about what was happened in server side, and they can also be passed in as alternative input values.

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ASP.Net: Add Client Side JavaScript Codes

ASP.Net controls do not support all the control events like window form application. For example, OnKeyUp, OnMouseUp, and OnMouseMove events. It make sense that if these events were supported, there would be too many calls from client side back server, and it would make aspx pages very very slow.

However, there are some cases you would like your aspx page to support these events. For example, I have a asp:TextBox control with an attribute of OnTextChanged event. This even only fires back to the server when you change the text and leave the control to any where on the same page. If you click on another link on the page right after you change the text, this event would not be called at all.

In order to catch this event and set a flag on the page to indicate a change, I have added another asp:TextBox control called MonitorChangeControl. Then I added the following codes in the Page_Load event to insert client side JavaScript function to the aspx page so that on the client side the MonitorChangeControl text will be changed to a text "Some values may have been changed." when my monitored textbox is changed:

string changeScript = "<script language='javascript'> function SomeValueChanged() {" +
  "document.getElementById('" + MonitorChangeControl.ClientID +
  "').value = 'Some values may have been changed.'; }</script>";
// Add the JavaScript code to the page.
if (!ClientScript.IsClientScriptBlockRegistered("SomeValueChanged"))
{
  ClientScript.RegisterClientScriptBlock(this.GetType(), "SomeValueChanged", changeScript);
}

After register the script function, then in the following codes I add an attribute "OnKeyUp" with a script call to the function "SomeValueChanged()":

TextBox myTextBox = WebPageUtil.FindControlRecursive(row, "curr_day"); //row is a GridViewRow
if (currValue != null)
{
  myTextBox.Attributes.Add("OnKeyUp", "return SomeValueChanged()");
}

When I run the aspx page in a browser, the TextBox is converted to an Input document element with an attribute like this:

<input name="..." OnKeyUp=""return SomeValueChanged()" .../>

This attribute will cause the client side event fired whenever the input element's text is changed or key-is-up.

So far so good. However, for an asp:CheckBox control, if the attribute is added in a the same way, the attribute is actually added to a span element in the aspx page which is outside of the input element (converted from CheckBox):

<span ... OnKeyUp="" ...><input id=... type="checkbox" .../></span>

Therefore, I have to add the attributes in a different way:

// row is a GridViewRow control and FindControlRecursive is my function.
CheckBox box = WebPageUtil.FindControlRecursive(row, "ValidatedCheckBox");
  if (box != null)
  {
    box.InputAttributes.Add("OnKeyUp", "return SomeValueChanged()");
    box.InputAttributes.Add("onmouseup", "return SomeValueChanged()");
  }

After that, I tried to view source from the browser. Here is the result of what I expected:

<input id=... type="checkbox" ... OnKeyUp="return SomeValueChanged()" onmouseup="return SomeValueChanged()" />

By the way, the event of OnChange is working for TextBox control but not for CheckBox controls. The OnChange is fired only after you make a change and at the moment whey you leave the control. For complete HTML element, properties/attributes, and events, see the page of HTML Event Attributes and JavaScript Event References.

For the function FindControlRecursive(), see my previous blog on May 29, 2008

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SqlContext.Pipe.Send not Available in SQL Server Project's Functions

I tried to use SqlContext.Pipe.Send to send a message back from a SQL project's funciton. It does not work at all. When the function is called, it throw an exception at the point SqlContext.Pipe.Send is called. It works fine in a SQL project' Stored Procedure.

Normally, I use this send to debug my program in the development stage. With this limitation, I have to create a stored procedure instead. After everything is fine, I then change it back to a function.

Another related issue about SQL Server Project, if I tried rename the previous deployed stored procedure as a way to back up the previous version of CLR SP, the SP is gone after I deploy my project again. It looks like that the deployment is smart enough to remove the previous version first, no matter you rename it or not. It does make sens since the new CLR assembly will be deployed and replace the old one. Even you rename it, the CLR SP should not be able to work since the assembly has been updated.

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Comparing Two Tables By SQL Stored Procedure

I have created a SQL Stored Procedure to compare any two tables based on Microsoft SQL Server 2005 new syntax EXCEPT and INTERCEPT. Basically, I used EXCEPT and UNION to get the result of differences between tables and INTERCEPT to get the same result of two tables.

In addition to that, the SP will compare two tables by specifying column fields and conditions and display the result by optional ORDER BY clause. Here is the SP:

CREATE procedure [dbo].[SP_CompareTables] (
 @table1 varchar(100),
 @table2 varchar(100),
 @table_colList varchar(3000) = NULL,
 @whereClause varchar(3000) = NULL,
 @orderByClause varchar(3000) = NULL,
 @difference0 int = 0
)
AS
  DECLARE @sql varchar(8000);
  DECLARE @colList varchar(3000);
BEGIN
  if ( @table_colList is null Or @table_colList = '' )
  begin
    set @colList = '*';
  end
  else
  begin
    set @colList = @table_colList;
  end
  if ( @difference0 = 0 )
  begin
   set @sql =REPLACE(REPLACE(REPLACE('
SELECT ''@table1'' AS TblName, *
FROM (
  SELECT @colList
 FROM @table1
 EXCEPT (
   SELECT @colList 
  FROM @table2)
) x
UNION ALL
SELECT ''@table2'' AS TblName, *
FROM (
  SELECT @colList
 FROM @table2
 EXCEPT (
   SELECT @colList
  FROM @table1)
) y', 
'@table1', @table1),
'@table2', @table2),
'@colList', @colList);
  end;
  else
  begin
    set @sql =REPLACE(REPLACE(REPLACE('
SELECT @colList
  FROM @table1
  INTERSECT (
    SELECT @colList 
 FROM @table2)', 
'@table1', @table1),
'@table2', @table2),
'@colList', @colList);
  end;
  if ( @whereClause is not null And len(@whereClause) > 0 )
  begin
    set @sql = REPLACE(REPLACE('
SELECT * FROM (@sql) v
WHERE @whereClause', 
'@sql', @sql),
'@whereClause', @whereClause);
  end
  if ( @orderByClause is not null And len(@orderByClause) > 0 )
  begin
    set @sql = REPLACE(REPLACE('@sql 
ORDER BY @orderByClause', 
'@sql', @sql),
'@orderByClause', @orderByClause);
  end;
  print @sql;
  exec(@sql);
  return 0;
END

To use this SP is very simple. For example, to compare two tables of [Employees] and [Employees_backup], you can just run the following script to compare two whole tables:

EXEC SP_CompareTables 'Employees', 'Employees_backup';

More examples by specifying columns, where clause and order clause:

EXEC SP_CompareTables 'Employees', 'Employees_backup', 'FirstName, LastName';
EXEC SP_CompareTables 'Employees', 'Employees_backup', 'FirstName, LastName', 
  'FirstName like ''D%'' AND BirthDate Between ''Jan 01, 1990'' AND ''Jul 30, 2008''';
EXEC SP_CompareTables 'Employees', 'Employees_backup', 'FirstName, LastName', 
  NULL, 'FirstName, BirthDate' , 1; -- get same results

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SQL Server Project (4)

I have to close this series articles on SQL Server Project. The final part will cover some special issues related to SQL Server Project.

The first issue is the connection to SQL server. As I mentioned in SQL Server Project (2), it is recommended to use the context connection since the CLR assembly is already in a SQL server running process. However, this connection can only be created once. You cannot create another context connection for other executions. Normally, you don't need another one in one stored procedure for example. However, if you create several SQL procedures, functions, and triggers in one dll, you might get exceptions if one calls another since only one context connection is allowed. You don't have control who is going to run these stored procedures, functions, or triggers.

Therefore, I think it is better to create one SQL item (SP, function or trigger) in one dll. You could create a normal SQL connection with catalog for a db table, user name, and password information in a connection string if you have to, and that connections can be created more than once. In a SQL server context, it does not make sense to do that unless you need to connect to another SQL server or Oracle server.

An related issue is that always to handle exceptions in your assembly and close any opened connections. As I mentioned before, the assembly is loaded to SQL server running process, and it would not unloaded automatically when your SP exits. The assembly may still in memory. If you don't handle exceptions, the opened connection will block the same SP being called again.

The second issue is that some assemblies may not work in SQL server project. I tried NHibernate and some other dlls as my references. What I found is that some assembly reflection functions are not working in SQL server. For example, I found that there always exceptions when these dlls try to load another assembly file to get class or property information. All these kind calls cause exceptions. This is very unfortunate and I think this is very bad limitation for SQL server project. I have no idea why and how exceptions would happen.

If you are going to write your SQL server project in C#, all the parameters in a SP have to be specified whey the SP is called, unlike MS Transact SQL SP could have default values for parameters.

The installation and deployment process for a SQL Server Project is a complicated one. As I mentioned in my previous articles, some asymmetric keys, log in permissions have to be created, and dependency assemblies have to be registered. The deployment of SQL server project is one click process if you have source codes and Visual Studio avalailbe. However, that click-only-once deployment may hide some SQL calls to register and set up all SPs, function and triggers. If you want to create an automation process in SQL, you have to keep all the assembly files available somewhere even they are not referenced after the installation and deployment. To uninstall it, the process is reverse. You have to remove all the SPs, functions, and triggers first, and then to delete assemblies, and then other dependency items. Since there are many things involved, anything wrong may cause your assembly not being functional.

I had a case that my CLR assembly SP did not work one day. It says about some permissions to load assembly failure. I tried to remove all the assembly and to re-install again, but I could not remove them as well. I was stuck in the middle. Finally I found it is the case SQL server was in low virtual memory. The error message actually was misleading. I restarted the SQL sever and reloaded files I did in the middle, then everything worked fine. Therefore, be prepared to handle all the uncertainties, document all the procedures in a well organized way and save all the source codes and dependency files in repository.

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SVN, Its Tools and Checkins

Subversion (SVN) is an open source version control system. I used it for source code control or repository. There are two open source SVN tools available for Windows and Visual Studio: TortoiseSVN and AnkhSVN.

Normally, I use Tortoise to check out source codes, a solution or project, to a folder and then it will create SVN client folders and files (hidden) to mark files as a copy out from a SVN reposity. Then, open the sln or project by VS. AnknSVN will detect this project is from SVN and prompt you AnkhSVN is available for use for the project.

If you make a change to a file, the file then is marked as a changed one with red icon. You can commit the change back to the SVN server or check in to the repository. Ankhn works well for editing files. However, it does not support file renaming. You have to remove the file and add a new one as two steps for renaming.

In many cases, I have to revert some changes or the whole changes by using Ankhn's context menu. Revert means no change to the file in local and re-copy the file from repository to local. In case of removing a file, you will be prompt to remove the file from the repository. If you choose Yes, this actually is commit or change to the repository! You cannot just revert the change to get it back. You have to revert to previous versions. If you have several check-ins in a day, it may be hard to find the correct one restored back. Therefore, if you want to make a trial change in local, do not remove the file from the repository. Then you can simply revert the local project back and use Update to refresh the local files if you do not want to commit the change.

If you removed file from local (not in the repository!), and verified the change is OK and want to commit you changes to the repository. Remember, the removed files are still in the repository after your check-in. Use Tortoise's repo-browser to open the repository and remove the file from the browser. That's another commit change to the repository.

In a sense, those SVN tools do not have a check out session, or SVN does not support check out set or locking a check out set. That means several developers can work on a same source code file at same time. Any developer can drop their change and that's fine for others. However, if one checks in the code file, others may have to merge their changes before check in. Ankh provides diff for comparing repository file to local files and will prompt, I think, you if your check out version has been changed by others.

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Add Colors to Codes

Today I did some change to my blog's template html page with some style sheet definitions from ASP.Net forums' colrcode.css.

To find the css file, you have to view its source codes and find link to css at the top of web page. There are several css files. To find the style definitions for programming codes, you can view the partial codes from the forum web page's program codes.

ASP.Net forums provide on-line posting editor with a tool bar to insert source codes with formatted HTML tags around programming source codes, such as C#, VB, SQL, XML, ASP.Net and others. That's why I choose ASP.Net forums' css. I can use its posting editor to get some formatted HTML codes and then post them to my blog. Since I use the same css file in my template, my source codes are marked with colors!

One color is missing in ASP.NET page: color for class, interface and intrinsic or predefined types. I added a new tag as classInterface in my template for these cases. You will see my example codes with colors!

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Calculate Number of Months from a Date

Here is a simple function to calculate number of months from a date to now:

public int NumberOfMonths(DateTime fromDate)
{
   int months;
   DateTime dt = DateTime.Now;
   months = dt.Month + dt.Year * 12 -
     (fromDate.Month + fromDate.Year * 12);
   return months;
}

It is simple and no need to add any comments. However, when I first tried to google it, I found some very complex codes to get number of months and they are not right. Finally, based those codes, I figured out that the calculation is simple.

You may use this function twice to get difference between two dates.

One note about this function is that if the input date value is a future time, the number of months is a negative value.

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Tools and Utilities

Tools and utility programs are essential helpers for programming. I learned a lots of tools from web, blogs and other people. I remembered that when I was working at one SCADA company about 7 years ago. One developer showed me Total Commander tool with his passion. He told me it is much better than Windows File Explorer and he cannot work without it.

Since then, I tried this tool and I fall in love with it. It helps a lot for file exploring, management, and software development. When I work any where, I always bring it with me.

Many other tools are also very good. Here is a list of tools Jean-Paul and Scott Handselman recommend:

• developer.tools.list


• Tools and Utlities

I like to read JP's blog. Some of his blogs recommended some really good tools.

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Find a Control in ASP.Net Page

One ASP.NET page is composed of one aspx or xml file for front-end UI design and a class either in C# or VB as server side codes related to the page and control events.

Unlike window form application, the code-behind class does not know controls on the page directly. You cannot directly access control instances. For example, a label or text box control within a GridView control's template.

Here is one function I use to get a control by id:

using System.Web.UI;
...
public class WebPageUtil
{
...
  public static T FindControlRecursive<T>(Control root, string id) where T: Control
    {
        T found = null;
        if (root != null)
        {
            found = root.FindControl(id) as T;
            if (found == null)
            {
                if (root.ID == id)
                {
                    found = root as T;
                }
                else if (root.Controls != null)
                {
                    foreach (Control ctr in root.Controls)
                    {
                        
                        found = FindControlRecursive(ctr, id);
                        if (found != null)
                        {
                            break;
                        }
                    }
                }
            }
        }

        return found;
    }
  ...
}

Where Control is a System.Web.UI.Control. It has FindControl() method. It can only find control within a container control, or root in this case. For example, in a GridView control named as GridView1, a TableCell control in a selected row (GridView1.Rows[0]) may contain some Label or TextBox controls, which are defined within aspx page GridView1 control's template.

However, this call only search for controls directly placed within the current control. If the control is within the next or even deep level, you have to loop its children Controls to call recursively.

I use generic type method call to make the method very simple to use. Here are some examples:

GridViewRow row = GridView1.Rows[e.RowIndex] // e is GridViewUpdateEventArgs object
LinkButton btnSave = WebPageUtil.FindControlRecursive<LinkButton>(row, "btnSave");
if (btnSave != null)
  btnSave.Visible = false;

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SQL Server Project (3)

In a SQL Server Project, all the SQL Server Objects (SSO), such as stored procedures (SP), must be defined as public static methods. All these methods are marked with Microsoft.SqlServer.Server Attributes, so that they can be deployed as SQL Server Objects.

Let's see how a SSO is called in SQL Sever. For example, when a SP is called first time, the SQL server will load the assembly library from the database, as I mentioned that all the assemblies have to be registered in a DB, into memory. Then the specified static method is called. After the SP finishes its job, however, the assembly stays in the memory forever. I tested this feature with a simple SP and a private static integer counter in its class. The counter increases by 1 for each call. The counter stays in the memory with its last call increment for several days.

This is a quite interesting feature of the deployed SSOs. Actually, if you think it in the context of SQL service process, it is not hard to understand it. The SQL service process loads the assembly into memory. Since static methods are global available, they will stays as long as the SQL service process stays.

However, this posts a problem most developers do not realize. They assume that when a call is finished, all the related resources should be released. If the assembly is not well designed, it may cause memory leaks in a SQL server. For example, if some resources are not cleaned, these resources are left in the memory for each call. You can imagine that if the SSOs were called constantly, it would cause memory leak. Another issue is that if some resources are static and not cleaned, these resources are occupied in memory. As a result, the first call is fine, but the next call may get exception since they cannot access these resources.

Therefore, you have to pay attention to all the cleaning jobs. Make sure that all the resources are freed after the execution, including the case of the execution being interrupted by clients. For example, you have to handle ThreadAbortException exception.

Talking about exception handling, it is not recommended to handle or hide all the exceptions. For example, if you design a Trigger, you may want some exceptions thrown to SQL server so that any related failure would cause the SQL server to roll back transactions. Therefore, if you know how to handle some exceptions, you can handle them, otherwise, leave them alone.

There is a way to clean assembly from memory in SQL server. Run the following command to clean all the unused cache and free up memory:

DBCC FREESYSTEMCACHE ('ALL')

I run this command in a daily job for cleaning memory used during a day.

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Python

Recently, I started to learn Python script language through Python Tutorial. It is a very interesting programming language. It is very powerful and unique. The reason I have interest in Python is that I read an article about Google's open source project. It mentioned that Google promotes this open source language. After reading several sections in the tutorial, I really like Python.

Another reason is that Apple's OS installs Python by default. It is a script language used as Apple's script language. I am going to learn and write some scripts. Python may be a good choice.

I just read a section about Class in Python. Within a Class, there are two types of members, one for attributes and another for methods. You don't need to define all the methods in a class. You can add or delete attributes to a class dynamically. It is really convenient. However, if you defines a attribute, you cannot dynamically to delete it.

Regarding del statement, you can use it to delete a definition of a class as well. If you create an instance of a class and then delete the class, the instance still works For example, you can still call the instance's attributes or methods. I think that the instance is created in memory like an object. In Python, every thing is object.

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SQL Server Project (2)

As mentioned in the links in the previous article, SQL Server Project provides some basics to connect to a SQL server and communicate with the server.

Here is a brief of these basics:

• Connect to SQL server by connection string "Context Connection=true" so that no need to specify database and authentication information for most cases, since the project is deployed to SQL debase and all the stored procedures, functions and others run in the context.


• Send messages back to SQL server by SqlContext.Pipe.Send() method. The method call has two overloads, one taking a string as its parameter, and another one IDataReader. To call this method, no connection is needed.


• Execute SQL statements through IDbCommand.ExecuteXXX() methods: ExecuteReader(), ExecuteNoneQuery(), and ExecuteScalar(). By using these methods, you can all SQL query and none query statements.

With all these basics, it looks that you can go ahead to create any SQL server database objects (stored procedure, function, triggers …). However, when I first time rolled my sleeves on a project, I encountered a problem. There was so limited number of references available in my Visual Studio project, about 5 only. There is no browse button for adding references neither. How can I use other Microsoft .Net libraries, as well as libraries I created?

To solve the problem, I finally realized that I have to understand the way how .Net assemblies are loaded and executed in a SQL server database. All the assemblies, including dependent assemblies, have to be registered in the server database. For example, if a stored procedure is defined in a .Net assembly, the assembly and its dependent assemblies have to be registered in a SQL server database. When the stored procedure is executed, the SQL server database will load the assembly and dependent ones from the database, not from local or remote file systems.

Therefore, if you want to add new references to your project, you have to register these libraries to the SQL server database first. The SQL server project’s reference dialog window lists only the libraries from the destination SQL server database.

To register a library to the SQL server database, you have to understand a few of additional concepts. First is the Permission set. To register an assembly, a Permission set has to be specified. There are three types: SAFE, EXTERNAL ACCESS, and UNSAFE. Try to register your libraries from SAFE mode first. If you get any error messages, you may have to try the next level till you can get them registered.

Permission sets are for security and reliability purposes. However, in most cases, you have no choice to use the least secured permission level. My understanding of those modes is that, if you run pure .Net managed codes and only for internal access, you should use SAFE mode. If you have to access to external resources such as file system, you have to use EXTERNAL ACCESS. If the libraries contain codes to access dynamical resources such as reflection load and web services or unmanaged codes, you have to no choice to UNSAFE. As a result, if you use some third party libraries, including many of Microsoft ones, you may end up with UNSAFE in most cases.

The second concept is that your assembly must be a strong named one if the permission mode is not SAFE. SQL server enforces this mandatory requirement for all none SAFE assemblies. If the assembly is not a strong named one, you have to sign it with a key by using the tool of sn.exe from Microsoft.

With these understandings, you are ready to register your dependency assemblies to a SQL server database. The followings are some SQL commands I used:

Add a key to assembly files

Signer.exe -k ..\..\myCompany_key.snk -outdir .\build -a *.dll

Add a strong name key and login permission for the key in SQL Server

Use master
IF EXISTS(SELECT * FROM sys.syslogins WHERE NAME = 'Assembly1_Login')
BEGIN
  DROP LOGIN Assembly1_Login;
END
IF EXISTS(SELECT * FROM sys.asymmetric_keys WHERE NAME = 'Assembly1_key')
BEGIN
  DROP ASYMMETRIC KEY Assembly1_key;
END
CREATE ASYMMETRIC KEY Assembly1_key FROM EXECUTABLE FILE = 'C:\Temp\bin\Assenbly1.dll';
CREATE LOGIN Assembly1_Login FROM ASYMMETRIC KEY Assembly1_key;
GRANT UNSAFE ASSEMBLY TO Assembly1_Login;

Register an assembly

DECLARE @asm VARCHAR(1024);
SET @asm = 'C:\Temp\bin\MyAssembly.dll';
IF  EXISTS (SELECT * FROM sys.assemblies asms WHERE asms.name = N'MyAssembly')
 DROP ASSEMBLY [MyAssembly]
CREATE ASSEMBLY [MyAssembly] FROM @asm WITH PERMISSION_SET = unsafe;

After your registration process, open your project in VS again. You should be able to add references to you project. I always save my registration process in a script. In case I have to reload my assemblies, or deploy the same one to another production database, I can use the script to do the job.

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