I usually use ItemsSource property when I need to databind a control in WPF because it’s straightforward and the framework does everything for me.

However, I came accross a situation where I had to do all data formatting and stuff for a DataGrid. In such a case the best method is to use the DataContext property.

The DataContext property is available for pretty much any item you use under the .net framework because it is implemented in the FrameworkElement. What you need to know about FrameworkElement to understand DataContext is that it is one of the very top level classes in the .net framework class hierarchy which is inherited by many classes beneath it.

The ItemsSource property on the other hand is implemented in the ItemsControl class which is located far below in the .net class hierarchy and therefore only inherited by a sub set of controls you use.

What is DataContext

As the name suggests this property sets the data context for an item. In other words it sets the bigger picture (something similar to saying this text box is should be bound to some data element within this particular data table, but you have to tell me what exactly that element is). So when you set the data context property, then you have to specify databindings explicitly.

Data context is usually used to databind controls such as forms which would include sub controls that need to be bound to sub elements of the data context.

For example, a form would include text boxes for First Name and Last Name. Instead of databinding each control you can set the datacontext property of the form so that both FirstName and LastName textboxes would get relevant data automatically.

Following example shows a simple use of DataContext:

First take a note at the two XAML lines for two text boxes which tells the framework what fields of the datacontext each text box should be bound to

Now following code sets the datacontext of the whole window. (Notice this.DataContext)

// create a simple data source
DataTable _dt = new DataTable();
_dt.Columns.Add(new DataColumn("Id", typeof(int)));
_dt.Columns.Add(new DataColumn("FirstName", typeof(string)));
_dt.Columns.Add(new DataColumn("LastName", typeof(string)));

_dt.Rows.Add(1, "Robin", "Hood");
_dt.Rows.Add(2, "Spider", "Man");
_dt.Rows.Add(3, "Knight", "Rider");

this.DataContext = _dt;

Output

ItemsSource

On the other hand, Items source setting does all the binding work for you so all you have to do is to set the items source property of your control to any collection that implements IEnumerable interface.

Following example shows how you can simply data bind a datagrid using ItemsSource property:

// create a simple data source
DataTable _dt = new DataTable();
_dt.Columns.Add(new DataColumn("Id", typeof(int)));
_dt.Columns.Add(new DataColumn("First Name", typeof(string)));
_dt.Columns.Add(new DataColumn("Last Name", typeof(string)));

_dt.Rows.Add(1, "Robin", "Hood");
_dt.Rows.Add(2, "Spider", "Man");
_dt.Rows.Add(3, "Knight", "Rider");

// DgTestGrid is a dimple datagrid
this.DgTestGrid.ItemsSource = _dt.DefaultView;

Output

Note

The data table, _dt is not used straightaway as the items source but its DefaultView is used instead. This is because the DataTable (System.Data.DataTable) class does not implement the IEnumerable interface but its DefaultView (System.Data.Dataview) does.

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Cassian Menol Razeek

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!

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Cassian Menol Razeek

I wouldn’t be wrong if I say the Brain is the most vital organ in the human body. As we all know brain handles most of critical operations inside our body such as keeping and managing memories, organizing our activities, keep other organs perform, and so much more.

The Brain, as most of us already know, works by sending electric signals through complex meshes of neurons so the brain has to maintain a good environment around to keep the accuracy of this electrical signal flow.

The environment inside the brain is the brain fluid so the ingredients or components of the brain fluids are very critical to the functionalities of brain.

Any organ of the body gets the supplies it needs through blood and so does the brain. Ingredients of human blood vary depending on the situation, food, problems of other organs, etc. so it is obvious that the blood is not the same all the time.

Not like other organs, the brain has to think a lot before extracting anything from blood because if the chemical levels of brain fluid vary it directly affects the signals passed through neurons. If the brain fluid is not maintained in an optimum level, the environment will become too noisy for neurons and sending signals would become like talking in the middle of a party.

So there is this Blood-Brain Barrier (which is also referred to as BBB) which extracts the necessary ingredients such as Oxygen and Glucose and make sure nothing else is taken in.

Blood-Brain Barrier Diagram

Photo courtesy: Malcolm Segal

Where is Blood-Brain Barrier Located?

BBB is located at the brain blood capillaries. These capillaries are unusual in several aspects from capillaries in other organs. Those aspects are briefly described below:

• The end-points of cells which make up the walls of these capillaries are sealed together at their edges by tight junctions which are a key component in the barrier. These junctions make sure that water soluble substances in the blood don’t pass between the edges of cells.
• These capillaries are enclosed by flattened cells which altogether called the ‘end-feet’ which also work as a (partial and active) barrier.
• The only way for water soluble substances in the blood is through the walls of capillaries. These walls plays the other role in the barrier because their cell membranes are made up of a lipid/protein belayed only allowing flat-soluble molecules including those of oxygen and carbon dioxide, anesthetics and alcohol to pass through the walls of capillaries.
• In the capillary wall there are three classes of ‘efflux pumps’ which pumps various lipid-soluble molecules back in to the blood out of the brain.

However, the brain needs water soluble compounds such as Glucose for energy production and amino acids for protein synthesis so there are these Carriers in the walls of capillaries which allow those compounds to go through the wall and move waste products and unwanted molecules in the opposite direction.

The blood-brain barrier plays another key role in keeping the volume of the brain at a constant level. Since the brain is contained inside a rigid skull it is important to keep the fluid from free movement thus keeping volume of the brain static.

Problems Related to BBB

Even though BBB is made in the sole purpose of protecting the brain, it has become a barrier to medicine to access the brain. Since many medicines are water soluble, they are barricaded at the BBB. This process has made it very hard to treat brain tumors and infections such as AIDS virus.

In fact, AIDS virus uses BBB as a shield by hiding behind the BBB from body defense mechanisms.

Due to such reasons medicine has to be made as fat-soluble but then a new problem arises because then the medicine will be absorbed by most cells of the body which may be toxic.

The alternatives are making drug molecules that can ride on natural transporter proteins or use drugs that can open the Blood-Brain-Barrier.

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Cassian Menol Razeek