MS SQL Server Isolation level explained

An isolation level determines the degree of data isolation between concurrent transactions. The default SQL Server isolation level is Read Committed. 

In the ascending order of isolation: Read Uncommitted, Read Committed, Repeatable Read, Serializable.

Read uncommitted: dirty read, you can read those that have been modified by other transaction but not yet committed. It does not issue shared locks to prevent other transactions from modifying data read by the current transaction.

Read committed: cannot read data that has been modified but not committed by other transactions, this prevents dirty reads. Data can be changed by other transactions between individual statements within the current transaction, resulting nonrepeatable reads or phantom data. Shared locks are only held for individual statements.

Repeatable read: cannot read data that has been modified but not yet committed by other transactions and that no other transactions can modify data that has been read by current transaction until current transaction completes. Shared locks are placed on all data read by each statement in the transaction and are held until the transaction completes. This prevents other transactions from modifying any rows that have been read by the current transaction. But other transactions can insert new rows, so the query statement of current transaction could return unrepeatable results. Shared locks are held to the end of a transaction instead of being released at the end of each statement as READ COMMITTED.

Serializable: is the highest level, where transactions are completely isolated from one another. It cannot read data that has been modified but not yet committed by other transactions. No other transactions can modify data that has been read by the current transaction until the current transaction completes. Also, other transactions cannot insert rows with key values that would fall in the range of keys read by any statements in the current transaction until current transaction completes. Range locks are placed in the range of key values that match the search conditions of each statement executed in the transaction, this means that if any of the statements in the current transaction are executed a second time, they will read the same set of rows. The range locks are held until the transaction completes.

A few ASP.NET, C# questions

Question: you care building a setup for your application. The application contains a custom control developed by you, which will be shared across multiple applications. How should you package the custom control?

A: Package the control in a Merge Module (.msm) and add the .msm file to a

Windows Installer project.

B: Package the control into a cabinet project (.cab) and add the .cab file

to a Windows Installer project.

C: Create a separate directory for the control and then package it in a

Windows Installer project along with the rest of the project files.

D: Package the control as a Web setup project and create a link to that

project from the Windows Installer project.

My answer: B

Question: If you want to place a status bar control named 'statusBar1' at the bottom of your windows Form, which of the following would be the correct property to set?

A. statusBar1.Dock = DockStyle.Bottom;

B. statusBar1.Lock = "Bottom";

C. Location(statusBar1) = DockStyle.Bottom;

D. statusBar1 = Placement.Down;

My answer: A

What namespaces must you declare in order to use a SqlConnection object?

A. Import System.Data.Sql;

B. using System.Data.Sql;

C. using System.Data.SqlClient;

D. using Sql.Data;

My answer: C

Question: Which type of DataSet is derived from the base DataSet class and then uses information in an XML Schema file (.xsd file) in order to generate a new class?

A. Untyped DataSet

B. Typed DataSet

C. XML DataSet

D. XSD DataSet

My answer: B

You want to accomplish the following with a Button Control:

1.) Add the button

2.) Add the Event Handler

3.) Trigger the event

which would be the correct segment of code to accomplish these tasks?

A.

Button b = new Button(new EventHandler(onButtonAction));

b.clicked = True;

B.

Button b = new Button(new EventHandler(onButtonAction));

b.clicked(1);

C.

Button b = new Button();

b.Click += new ButtonEventHandler(onButtonAction);

b.PerformClick();

D.

Button b = new Button();

b.Click += new ButtonEventHandler(onButtonAction);

b.clicked = True;

My answer: C

Question: You need to create a file name "File.txt" in the directory "C:/data". How should you go about doing this?

A.

File fs = New File;

fs.Name = "File.txt";

fs.Directory = "C:/data";

fs.Create();

B.

FileStream fs = File.Create("C:/data/File.txt");

C.

FileStream fs = New FileStream();

fs.Name = "File.txt";

fs.Directory = "C:/data";

fs.Create();

D.

Stream sw = File.Create("C:/data/File.txt");

My answer: B, but the directory must exists in advance

Which of the following statements are TRUE about XML serialization?

I. XML serialization serializes only the public fields and property values of an object into an XML stream.

II. XML serialization inlcude type information.

III. XML serialization requires a default constructor  to be declared in the class that is to be serialized.

IV. XML serialization requires all properties that are to be serialized as read/write properties. Read-only properties are not serialized.

A. I

B. I and II

C. I, III and IV

D. All of the above

My answer: C

XML serialization by default doesn't serialize read-only properties

It requires a parameterless constructor in order to allow xml serialization to succeed

Question: The following code is found in a windows Application:

this.openFileDialog1.Title = "Open File";

this.openFileDialog1.Filter = "Word Documents (*.doc) | *.doc | Excel Spreadsheets (*.xls) | *.xls";

this.openFileDialog1.FilterIndex = 1;

this.openFileDialog1.CheckFileExists = true;

this.openFileDialog1.ShowReadOnly = false;

this.openFileDialog1.ShowDialog();

Which of the following statement is TRUE about this code segment?

A. The code segment sets the Dialog Title to Open File

B. The code segment sets the default file type to Excel Spreadsheets.

C. The code sets the File List box to Word documents and Excel documents

D. A and C

E. All of the above

My answer: D

the code segment sets the default file type to Word document

Question: Which of the statements below concerning literals is TRUE?

I. Data can be assigned to literals.

II. In certain cases, a suffix is added so that literals can perform the calculation in a much better way.

III. Strings can have many characters and are sometimes enclosed within double quotes.

a. I

b. II

c. I and II

d. I and III

e. all of above

My answer: e

update shared assembly

Shortly after releasing a new windows service, you discovered that there is a calculation error in a shared assembly the application uses. You corrected the error and are ready to install the new assembly on the client computers. how should you perform to quickly install your updated assembly?

My answer: Copy over the shared assembly and then use GACUTIL to install it into global assembly

?? null coalescing operator

.NET 3.5 questions:

Q1: What is the output of the following code?

int a = 20;

int? b = 30;

int? c = null;

Console.WriteLine(a + c ?? b);

A1:

result is 30

int?  indicates b and c are nullable types 

The result of 20+null is null. 

?? operator checks whether the value of a+c is null, it returns a+c if it isn't null, returns b if it is null.
?? operator works for both reference and value types.

Q2: what is the output of the following code?
 

var s= "Hello";

s = 5;

s = 5++;

Console.WriteLine(s);

Cannot compile, error is "cannot implicitly convert type 'int' to 'string'