The RowFilter property of the DataView allows to use flexible string similar to SQL or LINQ to easily filter rows wihtout having to iterate through them.

I had to implement a fully flexible search module for a project I’m working on. The user had to be able to perform a string search on any field displayed on the gridview. The above mentioned RowFilter method is really handy to provide such a functionality due to increased efficiency.

Assume following example:

The data table (in the database)

Field Name         Data Type  

Name                String

DateOfBirth        DateTime

Data

Name                     DOB

John                      1976-10-12

Sophie                   1990-12-30

If you want to use the RowFilter to enable flexible searching (i.e. if the user type “j” in the search textbox the search grid view would only show the record for John) you can use following code:

string SearchFor = SearchTextBox.Text;
((DataView)SearchGrid.DataContext).RowFilter = string.Concat("Name LIKE '%", SearchFor, "%'");

This will allow the above explained behaviour so if the user now enter “h” in the textbox it will show both records because both John and Sophie have the letter “h” in their names.

So what if we repeat the same and use the following code for the date of birth field?

// WRONG CODE
string SearchFor = SearchTextBox.Text;
((DataView)SearchGrid.DataContext).RowFilter = string.Concat("DateOfBirth LIKE '%", SearchFor, "%'");

We would expect the program to filter records similarly. However, if you enter “1990″ in the search textbox hoping it would filter Sophie, it would give you an error instead!

This is because the LIKE operator cannot work with non-charactor types.

The Solution!

We have to use a converter to convert the datetime field into a string just before the RowFilter is applied.

Here’s the code:

string SearchFor = SearchTextBox.Text;
((DataView)SearchGrid.DataContext).RowFilter = string.Concat("CONVERT(DateOfBirth, System.String) LIKE '%", SearchFor, "%'");

The Convert function will cast the datetime value into string just before the LIKE operation takes place. And since the datetime value is only temperory converted, the original data are not affected as well.

So if you add this code to the previously worked code for the Name column as described below:

string SearchFor = SearchTextBox.Text;
((DataView)SearchGrid.DataContext).RowFilter = string.Concat("Name LIKE '%", SearchFor, "%'");
((DataView)SearchGrid.DataContext).RowFilter = string.Concat("CONVERT(DateOfBirth, System.String) LIKE '%", SearchFor, "%'");

The Result

Now if you type “John” the grid will only show records that match that value and if you type a digit (e.g. 30) it will show the record that has 30 in the dob field (i.e. the record for Sophie)

Note
You can use the same method for any other field type which doesn’t support use of LIKE directly.

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Cassian Menol Razeek

Timestamp is a value that is incremented by the database whenever an insert or update operation is performed.

Even though the name Timestamp could be a bit misleading, this value has no relevance to a clock related time. This only shows a linear progression of time.

For an example , it is something like your database saying it has been two update or insert commands since your last visit.

You can see this value by referring to @@DBTS  [ select @@DBTS ]

Database Timestamp Value

Well, in simple terms, this helps to keep track of versions of records.

For an example, assume a scenario where you have to fetch a record from a table, manipulate the data and write it back.

What if the record gets changed (from another database call) after you fetched data? You will manipulate the old data and update the record without knowing somebody has updated the record in between your fetching and updating commands.

How can timestamp help?

You can add a column to your table (you can call it “Version”) and set its data type to TimeStamp. Then whenever you update or insert a record to this table, this column will record the database timestamp after that transaction.

So before writing your manipulated data, you can check if the timestamp value remains the same as what you read at the beginning of the transaction.

Following example demonstrates how timestamp can be used to monitor versions:

The Person table used for this example has a column called “Version” which is of type Timestamp.

First simply query the Version column of the table for the person called “Robert”

Timestamp before update

Timestamp after update

Note: Timestamp columns are automatically updated by the database engine so you do not have to specify value when either inserting or updating a row of a table which has a timestamp (version) column.

So to insert a record to a table with a timestamp column simply omit the timestamp column from your insert statement.

i.e. – Person table has following columns [Id, Given_Name, Family_Name, Age, Version]

Insert statement would be:

Insert into Person(Id, Given_Name, Family_Name, Age)
Values(001, "Robert", "Nox", 78);

The database will take care of the timestamp (version) column.

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Cassian Menol Razeek

We all get that day when we get an exception complaining about the single quotation or apostrophe that was in our SQL statement.

The best advisable thing to do is to use stored procedures so that all data are passed as parameters. However there are situations we have to use in-line SQL statements and even there are situations where even SQL parameters cannot manage this issue.

For example, if you use the exec method in you stored procedure body to do some dynamic stuff [read more about using exec to generate dynamic queries in stored procedures here ] you will have noticed that even if you pass a string with an apostrophe to an sql parameter it will still throw an exception at you !

So the only way out is to escape this character. Once you instruct the SQL parser to escape the character it will take the apostrophe as part of the string input not part of the command.

How to?

Simply replace your apostrophe / single quotation with two apostrophes / two single quotations .

i.e.
Replace Bob’s world With Bob’‘s world  <- these are two single quotation characters (not one double quotation character)

This can be easily done by using the string.replace method.

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Cassian Menol Razeek

Have you ever wanted to write a flexible and dynamic stored procedure that would allow you to send the table name as a parameter?

Have you ever wanted to write a flexible and dynamic stored procedure that would allow you to send only the condition but also the column name you want to include in the where clause?

Well I did. I wanted to create a stored procedure that would take Table name, Criteria column name  and the Target criteria value as parameters and create the SQL query dynamically.

Usually, we have to write our SQL code in the stored procedure body where we cannot treat our sql statement as a string.

The way to achieve this, however, is by using the Exec method provided in SQL.

Exec (execute) allows you to execute a command or a character string that contains Transact-SQL command(s).

Without wasting more time, following is the code I used to achieve my goal:

CREATE PROCEDURE GetRowCountByStringColumn

@TableName nvarchar(50),
@CriteriaColumnName nvarchar(50),
@CriteriaValue nvarchar(150)
AS
BEGIN

EXEC('SELECT  Count(*) FROM ' + @TableName
+ ' WHERE ' + @CriteriaColumnName + ' = ''' + @CriteriaValue + '''')

END
GO

As you can see the procedure takes three arguments:

TableName
CriteriaColumnName – the name of the column that should be checked in the where clause
CriteriaValue – the value the Criteria Column Name should be checked against

The exec command creates the SQL command (at run time) and executes it.

This helped me to create many dynamic stored procedures for my current project and saved me from having to create stored procedures for each table.

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Cassian Menol Razeek

We frequently get to fetch data from the database, update them and then write them back to the database.

Most of the time we only have to write them back as individual records.

How about updating a whole database table in the memory and having to synchronize all changes to the actual data table?

My initial thought was this would be full of complex coding. However, thanks to Microsoft, there’s nothing much to be done at all.

So how are we gonna do this is…

We will use a data adaptor to fill our data table as usual.

The only new thing is the use of a Command Binder.

Command Binder: A command binder is capable to detect changes that have occurred to a table (in the memory) and then automatically generate appropriate SQL statements to save those changes into the actual data table (in the database).

Following is a simple example: Scenario: In my application I had to take a database table name and present data in a data grid and then save all changes made by the user.

What we need: a data table an adaptor a connection a command builder I have defined them at the form level so I can use them across the form from different events.

private DataTable _tbl;

private SqlDataAdapter _adptr;

private SqlConnection _conn;

private SqlCommandBuilder _cbldr;

Step1: Initialize connection and retrieve data from the database

_tbl = new DataTable();
_conn = FetchData.GetOpenConnection();
_adptr = new SqlDataAdapter("Select * from " + DatabaseTableName, _conn);
_cbldr = new SqlCommandBuilder(_adptr);
_adptr.Fill(_tbl);

Step2: Let the user to change data (in here simply bind the table to a grid)

dgMainGrid.DataSource = _tbl;

Step3: Save (synchronize) changes to the actual database table Even though this is a complex process and undoubtedly would take a lot of effort to do manually, Thanks to .net framework all we need is a line of code.

_adptr.Update(_tbl);

Once you call the adaptor to update the table, it will use the command builder attached to it to generate all necessary SQL command building. The database table is now up-to-date!

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Cassian Menol Razeek

English is not my first language so I use online dictionaries frequently as a part of my daily routine to clarify and learn unfamiliar words as I read through articles in the Internet.

I have been using www.ditionary.com for a long time and I had the plan to make this work easy by creating a small application to retrieve the definition with support of a web service. This morning suddenly a new idea hit me to use JavaScript to get the word in the first place and load the appropriate URL.

How Does This Work?

When a user enters a word in the www.dictionary.com interface it redirects the user to the following dynamic URL.

http://dictionary.reference.com/browse/Target-Word

Target-Word is The word we are seeking the definition for

What this JavaScript does is it retrieves the desired word from the user via a prompt, generate the appropriate URL according to the above format and open the new URL in a new window or tab so the time taken (under normal circumstance) to, load the web site, type-in the word, wait till the site redirects you, is saved. Now time is only taken for a single server request/response.

How To Set This Up?

It’s simple, just add a new favorite (for IE) or bookmark (for FireFox) in your browser and paste following code as the URL (for IE) or Location (for FireFox):

javascript:(function(){var%20word=prompt(%22Enter Word:%22);if(word!=null){window.open(%22http://dictionary.reference.com/browse/%22+word);}})();

Add bookmark dialog box in firefox

Now, when you open the favorite/bookmark, it will ask you for the word you want to look for and open the definition in a new window/tab.

Sample use of the script

It’s easier to use if you add the bookmark/favorite as a button into your bookmark/links toolbar

Bookmark button

This small script helps me a lot daily so I hope this would help you too!

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Cassian Menol Razeek

I have being working on a software application made on .Net and recently my client asked me to use D LINQ instead of SQL.

D LINQ has great benefits loaded! As I started working with DLINQ I started to know that preventing SQL injection is not a headache anymore and misspelled SQL queries will not trouble agian at run time because DLINQ generates all necessary SQL inside the framework!

I chose to use annotations inside the class instead of using separate xml file. Following is a part of the first class I ported to D LINQ.

</p>
_
Public Class Process
_
Public ProcessID As Integer
_
Public BusinessProcessID As String
_
Public ProcessText As String
...
...

ProcessID column is the primary key of my database table tbl_Process.

Important Point: I use database to auto-generate values for the primary key column (integer value incremented by one).

So when I run the application, It gave me this unexpected error:

Cannot insert explicit value for identity column in table ‘tbl_Process’ when IDENTITY_INSERT is set to OFF.

Basically, the IDENTITY_INSERT when using the database to auto generate value for a field but when I ran a SQL insert statement at the database end it worked fine!

After some tough time I found out the solution for this problem!

When we use an auto-generate field in a data table we have to specifically mention it in the matching field in the appropriate class.

The code to state this is:

Syntax:

IsDbGenerated:=True

This has to be added to the annotation added for the specific column like:

</p>
_
Public ProcessID As Integer

Now D LINQ can understand that the field value is auto-generated by the database!

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Cassian Menol Razeek

I have been working with many survey sites in the Internet and I have learnt a lot of lessons. I learnt some of these when I was researching about online survey sites and most of these lessons are learnt by experience. So I thought to share my knowledge with the rest of the world hoping it would help someone out there.

So in this article, I will give a set of advices that I have learnt in the hard way…

Rule 1 – Don’t Select Survey Sites From Lists Rated By Other People

Many people in the Internet are involved in affiliate marketing. Many surveying sites pay bloggers when they refer a new person to their site. So don’t believe in those lists such as “Top 10 Most Paid Survey Sites”, “Top 5 Survey Companies”, etc. because the TOP site of those lists is the site that pays the blogger most! So my advice is not to believe in those ranked lists.

Rule 2 – Ask the site this question: ” What Do I Get For Responding To Surveys? “

The answer depends on the site you are going to work with. Some sites pay money and some sites pay by other means such as coupon codes and sweepstakes entries while some sites are charity sites where you get non-paid public service surveys.

Rule 3 – Work Only For Cash

As I mentioned there are many sites which pays you in indirect methods such as coupon codes. My advice is never work on surveys unless they pay you by money because there is no way to measure the value of your work. They will give you a coupon code or sweepstakes entry at the end of your days work and you still have to go around the corner to get your own earnings. Since most of the times these are given as discounts, you have to spend more money and buy something to apply those discounts. In simple words, you only feel you earn but you never get your earnings into your hands.

The worst problem is some coupon codes may not be useful for you at the moment and some discounts may not be available in your region. You have to take this very seriously if you are not living in the same country or region as the origin of the site where it is operational.

Rule 4 – Check Available Payment Methods

Your computer may simply get surveys through the site without any problems or delays but it doesn’t mean your payment gets to your bank account in the same speed. Go and check the payment options supported by the site. Some sites support various payment methods while some sites only have one or two methods.

For most payment methods there are limitations across countries. This isn’t a problem if you are located in the same country where the site is operational but if you are living in a different region or a country you have to be more concerned about this matter.
For an example, you may be able to create a Paypal account from your country but you may not be able to accept payments to that account because Paypal doesn’t support that service in your country. In such situations if your site does not have suitable options you may lose your money.

Rule 5 – Don’t Go After Fortunes

There’s no such thing as easy money! Remember this as you go on finding for survey sites because you will face sites that say they would pay bulks of money for each survey. My advice according to what I have learnt so far is don’t go for those sites because the more money they promise, the more chances for that site to be a scam. Unfortunately, many people around the world get into these scams everyday. The best thing is to find a site that pays a reasonable and especially practical price for your work.

Rule 6 – Work Hard! There’s No Boss To Push You Forward!

If you are working in a company then you have a boss looking at you to make sure you meet company expectations and to kick you off if you lose performance. In this case, you are your own boss. The good news is there’s no one to kick you off and you own everything you earn. The bad news is you have to take care of everything. Especially you have to keep your motivation up. It’s not easy to do something of your own without postponing. You must dedicate yourself to the work at least till you reach a solid level of ground to stand on.

In this new office you don’t have office times. You have your freedom and at the same time you have all responsibilities on your shoulders. In simple words, It’s your baby go ahead and grow it!

Don’t look for fortunes, Work hard and make your own fortune!

Was this post helpful to you? How can I improve? – Your comment is highly appreciated!

Cassian Menol Razeek

I wanted to select multiple rows of the grid view using check boxes to select each row.

In this post I will discus how and what I did to achieve this goal…

I used a template column which holds a check box to select or de-select a row in the grid view.

Adding a Template Column:

There are several simple ways to add a template column/field to your grid view:

1. Select your grid view and then click on the small task button (the small square button located to the top right corner of the grid view control) and select “Add New Column…” from the “GridView Tasks” box.
   1. Use “TemplateField” as the field type
   2. Provide a header text
   3. click ok
2. Or… Select “Edit Columns…” from the “GridView Tasks” box and
   1. Select “TemplateField” from the “Available fields: ” section
   2. Click “Add” button
   3. Provide a header text in the “TemplateField properties: ” section
   4. click ok
3. Or… Select “Columns” from the grid view properties and follow the steps described in the earlier method (2^nd one)

Adding a Checkbox to the Template Column:

1. Select “Edit Templates” from the “GridView Tasks” box. Then it will show you the inside of the template.
2. Select “Item Template” from the “Display: ” drop down list.
3. Drag and drop a check box in the item template area.
4. Give an id as “chkid” for the check box – You can use a different name if you want but make sure you don’t confuse when I use this name in later parts of this article.
5. Click “End Template Editing” from the “GridView Tasks” box.

If you have completed the above steps correctly, you should see the expected checkbox column added in to the grid view.

As you can see in the image above, in my example I use a Name column along with the check box column to make this clearer.

How to Databind the Template Field:

I use a datatable to populate the gridview so we have to databind our two columns.

The second column name is a “BoundField” so to databind it simply specify the name of the data table column you want to bind to this column in “DataField” property under “Data” property set in the fields dialog box you get when adding the second column (use one of the ways I described above to add a column).

Databinding the template field is a bit tricky, but not hard.

1. Click “Edit Templates” from the “GridView Tasks” box so that you will see the check box.
2. Click on the small button with a triangle in the upper right corner of the check box which is similar to the one we clicked on the grid view to get the “Checkbox Tasks” box and then click on the “Edit Databindings…” link inside that box.

You can use this dialog box to bind any property of the control to a data source column

In this example we will bind the “Checked” property of our check box to a Boolean column called “Selected” of the data source.

For that:

• Select “Checked” from the Bindable Properties section and enter following in the Custom Binding section:
  • DataBinder.Eval(Container, “DataItem.Selected“)
• Note: the word “Selected” (in red color) refers to the “Selected” field of the data source.

Populating the GridView:

As I described earlier I create a simple data table in the page load, populate it with some dummy data and then bind the grid view with it.

Note: I have used several methods to add data to a table to illustrate those to you.

The Code:

protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
DataTable dt = new DataTable();
dt.Columns.Add(new DataColumn("Selected", System.Type.GetType("System.Boolean")));
dt.Columns.Add(new DataColumn("Name", System.Type.GetType("System.String")));

DataRow dr = dt.NewRow();
dr.ItemArray = new object[] { false, "Cassian" };
dt.Rows.Add(dr);
dt.Rows.Add(new object[] { false, "Menol" });
dt.Rows.Add(new object[] { false, "Razeek" });

this.GridView1.DataSource = dt;
this.GridView1.DataBind();
}
}

There are several things that I’d like to bring to your notice:

• I have checked for postback to make sure this data population is not occurred in general post backs. The reason is the framework refreshes when the grid view is re-bound.
• So if we don’t do this check, whenever we click on a check box, a postback occurs, the grid gets refreshed, the check boxes get cleared, we cannot keep track of what check boxes are selected…!
• As illustrate in my code, you can either first populate a datarow and then add it to the datatable
• Or you can directly add the items using only one line of code.

Retrieving the Status of Checkboxes:

Now we have completed the interface and the user now can select several rows of the grid view using the appropriate check box.

The next step is to capture the rows that the user has selected.

In my example, I have used a button, once clicked; it will display the list of names of the selected people.

I will introduce the code first and then explain it to you.

protected void Button1_Click(object sender, EventArgs e)
{
ArrayList names = new ArrayList();
foreach (GridViewRow gvr in this.GridView1.Rows)
{
if (((CheckBox)gvr.FindControl("chkid")).Checked == true)
{
names.Add(gvr.Cells[1].Text);
}
}

this.Label1.Text = string.Empty;
foreach (object itm in names)
{
this.Label1.Text += " " + itm.ToString();
}
}

Note following:

• The code iterates through each row of the grid view using a for each loop, takes the Name field from the selected rows and then adds those names into a arraylist
• The GridViewRow refers to a single row in a grid view
• Control Control.FindControl(string controlID) – GridViewRow class provides this method to find a specific control within a grid view row. This method becomes very handy in situations like this where we cannot directly access the control from the code because those are generated at run time
• FindControl returns a control so you have to explicitly cast the returned control to the type of it

Screen Shot:

Conclusion:

We can use a template field with a checkbox to allow user to select multiple rows using checkboxes associated to each row. When the button is clicked, checkbox of each row is checked for its status and the row is selected if the user has chosen it.

Was this post helpful to you? How can I improve? – Your comment is highly appreciated!

Cassian Menol Razeek

Today I was experimenting on a grid view where I was trying to select multiple rows of the grid view using a check box column.

I wrote some code in the CheckedChanged of checkbox but then I found that the code was not executed when the state of the checkbox is changed.

So I did a little googling and found out about this AutoPostBack property. This property defines whether the control should post back to the server each time when the user interacts with the control. Or, according to this scenario, a post back will fire when the user clicks on the check box or when the Checked property is changed.

AutoPostBack :

This value holds a boolean value (true/false)

If the property is set to true, a post back is sent immediately to the server and no post back is occurred when set to false.

The Use of AutoPostBack:

According to MSDN, for most WebControls, when AutoPostBack is false, only the events from actions that cause a net change in the state of the control are submitted to the server.

In other words some events are not queued to the server. For example no event is fired when a user selects a value from a drop down list or when user presses Enter or Tab key after entering a value to a textbox.

If you want such events to be fired then you have to enable autopostback by setting autopostback property to true.

How AutoPostBack Works :

When AutoPostBack is enabled, the .Net framework automatically injects following additional items into the generated HTML code.

1. Two Hidden variables with name __EVENTTARGET and __EVENTARGUMENT
2. A Java script method with name __doPostBack (eventtarget, eventargument)
3. OnChange JavaScript event to the control

What is __EVENTTARGET :

__EVENTTARGET tells the server which control wants to fire the event so that the framework can fire the event on that control.

What is __EVENTARGUMENT :

__EVENTARGUMENT can be used to provide additional information to the server about the event.

What is __doPostBack (eventtarget, eventargument) :

Parameters sent to this method holds relevant target and event argument values and this method sets those values into __EVENTTARGET and __EVENTARGUMENT hidden variables so that the server can read those.

Then this method submits the form to the server where the appropriate event will be fired.

What is OnChange JavaScript event to the control :

Every control has a client side event called OnChange. When AutoPostBack is enabled for a control the framework sets the handler for this client side event as the __doPostBack method and will pass the name of the control as the first parameter, eventtarget.

Ex/

Following shows how the framework binds the __doPostBack method to the OnChange event.

<input type=”checkbox” onclick=“javascript:setTimeout(‘__doPostBack(‘CheckBox1′,”)‘, 0)” />

Was this post helpful to you? How can I improve? – Your comment is highly appreciated!

Cassian Menol Razeek

Recommended Books:

• Pro ASP.NET 3.5 in C# 2008

• Professional ASP.NET 2.0 Special Edition
• Beginning ASP.NET 3.5: In C# and VB Languages