Wednesday, October 14, 2009
Thursday, October 8, 2009
How do I get the IDENTITY / AUTONUMBER value for the row I inserted?
To get the indentity value of table we can use any of these:
1) INDENT_CURRENT : - IDENT_CURRENT returns the last identity value generated for a specific table in any session and any scope.
SELECT IDENT_CURRENT(’tablename’):- It returns the last IDENTITY value produced in a table, regardless of the connection that created the value, and regardless of the scope of the statement that produced the value.IDENT_CURRENT is not limited by scope and session; it is limited to a specified table. IDENT_CURRENT returns the identity value generated for a specific table in any session and any scope.
2) @@IDENTITY :- @@IDENTITY returns the last identity value generated for any table in the current session, across all scopes.
SELECT @@IDENTITY :- It returns the last IDENTITY value produced on a connection, regardless of the table that produced the value, and regardless of the scope of the statement that produced the value.@@IDENTITY will return the last identity value entered into a table in your current session. While @@IDENTITY is limited to the current session, it is not limited to the current scope. If you have a trigger on a table that causes an identity to be created in another table, you will get the identity that was created last, even if it was the trigger that created it.
3) SCOPE_IDENTITY :- SCOPE_IDENTITY returns the last identity value generated for any table in the current session and the current scope.
SELECT SCOPE_IDENTITY() :- It returns the last IDENTITY value produced on a connection and by a statement in the same scope, regardless of the table that produced the value.SCOPE_IDENTITY(), like @@IDENTITY, will return the last identity value created in the current session, but it will also limit it to your current scope as well. In other words, it will return the last identity value that you explicitly created, rather than any identity that was created by a trigger or a user defined function.
Examaple of each:
Create Table #Table
(
Id int identity(1,1),
[name] varchar(10)
)
insert into #Table
select 'P'
insert into #Table
select 'S'
insert into #Table
select 'G'
insert into #Table
select 'PP'
select * From #Table
Select @@Identity As InsertId,IDENT_CURRENT('#Table') As InsertId,SCOPE_IDENTITY() As InsertId
Drop table #Table
------------------------------------------
Note : To avoid the potential problems associated with adding a trigger later on, always use SCOPE_IDENTITY() to return the identity of the recently added row in your T SQL Statement or Stored Procedure.
1) INDENT_CURRENT : - IDENT_CURRENT returns the last identity value generated for a specific table in any session and any scope.
SELECT IDENT_CURRENT(’tablename’):- It returns the last IDENTITY value produced in a table, regardless of the connection that created the value, and regardless of the scope of the statement that produced the value.IDENT_CURRENT is not limited by scope and session; it is limited to a specified table. IDENT_CURRENT returns the identity value generated for a specific table in any session and any scope.
2) @@IDENTITY :- @@IDENTITY returns the last identity value generated for any table in the current session, across all scopes.
SELECT @@IDENTITY :- It returns the last IDENTITY value produced on a connection, regardless of the table that produced the value, and regardless of the scope of the statement that produced the value.@@IDENTITY will return the last identity value entered into a table in your current session. While @@IDENTITY is limited to the current session, it is not limited to the current scope. If you have a trigger on a table that causes an identity to be created in another table, you will get the identity that was created last, even if it was the trigger that created it.
3) SCOPE_IDENTITY :- SCOPE_IDENTITY returns the last identity value generated for any table in the current session and the current scope.
SELECT SCOPE_IDENTITY() :- It returns the last IDENTITY value produced on a connection and by a statement in the same scope, regardless of the table that produced the value.SCOPE_IDENTITY(), like @@IDENTITY, will return the last identity value created in the current session, but it will also limit it to your current scope as well. In other words, it will return the last identity value that you explicitly created, rather than any identity that was created by a trigger or a user defined function.
Examaple of each:
Create Table #Table
(
Id int identity(1,1),
[name] varchar(10)
)
insert into #Table
select 'P'
insert into #Table
select 'S'
insert into #Table
select 'G'
insert into #Table
select 'PP'
select * From #Table
Select @@Identity As InsertId,IDENT_CURRENT('#Table') As InsertId,SCOPE_IDENTITY() As InsertId
Drop table #Table
------------------------------------------
Note : To avoid the potential problems associated with adding a trigger later on, always use SCOPE_IDENTITY() to return the identity of the recently added row in your T SQL Statement or Stored Procedure.
Tuesday, October 6, 2009
Basic Differences in .Net
- Difference between == and .Equals Method?
- Difference between Close() and Dispose() Method
- Difference between Copy and Clone Method
- Value Type Vs Reference Type
- Struct Vs Class
- Static Member, Static Method, Static Constructor
- Difference between ADO and ADO.net Technology
- Difference between ADO.net Dataset and ADO Recordset
- Localization Vs Globalization
- Difference Between String and StringBuilder
- Response.Redirect(url,true) Vs Response.Redirect(url,false)
- Finalize Method Vs Destructor
- Difference between ExecuteReader, ExecuteNonQuery and ExecuteScalar.
- Difference between Dataset and DataReader
- “out” keyword Vs “ref” keyword
1.
What is Difference between == and .Equals() Method?
For Value Type: == and .Equals() method usually compare two objects by value.
For Example:
int x = 10;
int y = 10;
Console.WriteLine( x == y);
Console.WriteLine(x.Equals(y));
Will display:
True
True
For Reference Type: == performs an identity comparison, i.e. it will only return true if both references point to the same object. While Equals() method is expected to perform a value comparison, i.e. it will return true if the references point to objects that are equivalent.
For Example:
StringBuilder s1 = new StringBuilder(“Yes”);
StringBuilder s2 = new StringBuilder(“Yes”);
Console.WriteLine(s1 == s2);
Console.WriteLine(s1.Equals(s2));
Will display:
False
True
In above example, s1 and s2 are different objects hence “==” returns false, but they are equivalent hence “Equals()” method returns true. Remember there is an exception of this rule, i.e. when you use “==” operator with string class it compares value rather than identity.
When to use “==” operator and when to use “.Equals()” method?
For value comparison, with Value Tyep use “==” operator and use “Equals()” method while performing value comparison with Reference Type.
2.
Difference between Close() and Dispose() Method
Close() Vs Dispose Method
The basic difference between Close() and Dispose() is, when a Close() method is called, any managed resource can be temporarily closed and can be opened once again. It means that, with the same object the resource can be reopened or used. Where as Dispose() method permanently removes any resource ((un)managed) from memory for cleanup and the resource no longer exists for any further processing.
Example showing difference between Close() and Dispose() Method:
using System;
using System.Data;
using System.Data.SqlClient;
public class Test
{
private string connString = "Data Source=COMP3;Initial Catalog=Northwind;User Id=sa;Password=pass";
private SqlConnection connection;
public Test()
{
connection = new SqlConnection(connString);
}
private static void Main()
{
Test t = new Test();
t.ConnectionStatus();
Console.ReadLine();
}
public void ConnectionStatus()
{
try
{
if(connection.State == ConnectionState.Closed)
{
connection.Open();
Console.WriteLine("Connection opened..");
}
if(connection.State == ConnectionState.Open)
{
connection.Close();
Console.WriteLine("Connection closed..");
}
// connection.Dispose();
if(connection.State == ConnectionState.Closed)
{
connection.Open();
Console.WriteLine("Connection again opened..");
}
}
catch(SqlException ex)
{
Console.WriteLine(ex.Message+"\n"+ex.StackTrace);
}
catch(Exception ey)
{
Console.WriteLine(ey.Message+"\n"+ey.StackTrace);
}
finally
{
Console.WriteLine("Connection closed and disposed..");
connection.Dispose();
}
}
}
In the above example if you uncomment the "connection.Dispose()" method and execute, you will get an exception as, "The ConnectionString property has not been initialized.".This is the difference between Close() and Dispose().
Close() Vs Dispose Method
The basic difference between Close() and Dispose() is, when a Close() method is called, any managed resource can be temporarily closed and can be opened once again. It means that, with the same object the resource can be reopened or used. Where as Dispose() method permanently removes any resource ((un)managed) from memory for cleanup and the resource no longer exists for any further processing.
Example showing difference between Close() and Dispose() Method:
using System;
using System.Data;
using System.Data.SqlClient;
public class Test
{
private string connString = "Data Source=COMP3;Initial Catalog=Northwind;User Id=sa;Password=pass";
private SqlConnection connection;
public Test()
{
connection = new SqlConnection(connString);
}
private static void Main()
{
Test t = new Test();
t.ConnectionStatus();
Console.ReadLine();
}
public void ConnectionStatus()
{
try
{
if(connection.State == ConnectionState.Closed)
{
connection.Open();
Console.WriteLine("Connection opened..");
}
if(connection.State == ConnectionState.Open)
{
connection.Close();
Console.WriteLine("Connection closed..");
}
// connection.Dispose();
if(connection.State == ConnectionState.Closed)
{
connection.Open();
Console.WriteLine("Connection again opened..");
}
}
catch(SqlException ex)
{
Console.WriteLine(ex.Message+"\n"+ex.StackTrace);
}
catch(Exception ey)
{
Console.WriteLine(ey.Message+"\n"+ey.StackTrace);
}
finally
{
Console.WriteLine("Connection closed and disposed..");
connection.Dispose();
}
}
}
In the above example if you uncomment the "connection.Dispose()" method and execute, you will get an exception as, "The ConnectionString property has not been initialized.".This is the difference between Close() and Dispose().
3.
What is the difference between Copy and Clone Method.
Copy Vs Clone Method
Clone will copy the structure of a data where as
Copy will copy the complete structure as well as data .
Copy will copy the complete structure as well as data .
4.
Value Type and Reference Type Concept in .Net
A variable is value type or reference type is solely determined by its data type.
Eg: int, float, char, decimal, bool, decimal, struct, etc are value types, while object type such as class, String, Array, etc are reference type.
Value Type
1) As name suggest Value Type stores “value” directly.
2) For eg:
//I and J are both of type int
I = 20;
J = I;
int is a value type, which means that the above statements will results in two locations in memory.
3) For each instance of value type separate memory is allocated.
4) Stored in a Stack.
5) It Provides Quick Access, because of value located on stack.
Reference Type
1) As name suggest Reference Type stores “reference” to the value
2) For e.g.:
Vector X, Y; //Object is defined. (No memory is allocated.)
X = new Vector(); //Memory is allocated to Object. //(new is responsible for allocating memory)
X.value = 30; //Initialising value field in a vector class
Y = X; //Both X and Y points to same memory location. //No memory is created for Y.
Console.writeline(Y.value); //displays 30, as both points to same memory
Y.value = 50;
Console.writeline(X.value); //displays 50
Note: If a variable is reference it is possible to indicate that it does not refer to any object by setting its value to null;
3) Reference type are stored on Heap
4) It provides comparatively slower access, as value located on heap
Note:
The behavior of strings is different, strings are immutable (unchangeable) if we alter a strings value, we create an entirely new string), so strings don’t display the typical reference-type behavior. Any changes made to a string within a method call won’t affect the original string.
A variable is value type or reference type is solely determined by its data type.
Eg: int, float, char, decimal, bool, decimal, struct, etc are value types, while object type such as class, String, Array, etc are reference type.
Value Type
1) As name suggest Value Type stores “value” directly.
2) For eg:
//I and J are both of type int
I = 20;
J = I;
int is a value type, which means that the above statements will results in two locations in memory.
3) For each instance of value type separate memory is allocated.
4) Stored in a Stack.
5) It Provides Quick Access, because of value located on stack.
Reference Type
1) As name suggest Reference Type stores “reference” to the value
2) For e.g.:
Vector X, Y; //Object is defined. (No memory is allocated.)
X = new Vector(); //Memory is allocated to Object. //(new is responsible for allocating memory)
X.value = 30; //Initialising value field in a vector class
Y = X; //Both X and Y points to same memory location. //No memory is created for Y.
Console.writeline(Y.value); //displays 30, as both points to same memory
Y.value = 50;
Console.writeline(X.value); //displays 50
Note: If a variable is reference it is possible to indicate that it does not refer to any object by setting its value to null;
3) Reference type are stored on Heap
4) It provides comparatively slower access, as value located on heap
Note:
The behavior of strings is different, strings are immutable (unchangeable) if we alter a strings value, we create an entirely new string), so strings don’t display the typical reference-type behavior. Any changes made to a string within a method call won’t affect the original string.
Difference between Struct and Class
Struct are Value type and are stored on stack, while Class are Reference type and are stored on heap.
Struct “do not support” inheritance, while class supports inheritance. However struct can implements interface.
Struct should be used when you want to use a small data structure, while Class is better choice for complex data structure.
Choosing between struct and class
Use of structure in following condition is desirable.
When you have small data structure
Data Structure does not require to extent the functionality.
When you want to perform faster operation on data structure. (As structure are stored on stack, operation performed on it are faster.)
Use of class in following condition is desirable.
When you have complex data structure
Data Structure requires to extend functionality.
When you want to optimize memory usage. (As class is stored on heap, they are about to be garbage collected when no reference pointing to an object.)
What is the difference between instantiating structures with and without using the new Keyword?
When a structure is instantiated using the new keyword, a constructor (no-argument or custom, if provided) is called which initializes the fields in the structure. When a structure is instantiated without using the new keyword, no constructor is called. Hence, one has to explicitly initialize all the fields of the structure before using it when instantiated without the new keyword.
6.
Static Members of the class
“static members” belong to the whole class rather than to individual object
How to access static member of class?
Static members are accessed with the name of class rather than reference to objects. Example: className.StaticMemberName
Example of Static Member
class Test
{
public int rollNo;
public int mathsMarks;
public static int totalMathMarks;
}
class TestDemo
{
public static void main()
{
Test stud1 = new Test();
stud1.rollNo = 1;
stud1.mathsMarks = 40;
stud2.rollNo = 2;
stud2.mathsMarks = 43;
Test.totalMathsMarks = stud1.mathsMarks + stud2.mathsMarks;
}
}
Static Method of the class
- Static Method is Method that you can call directly without first creating an instance of a class. Example: Main() Method, Console.WriteLine()
- You can use static fields, methods, properties and even constructors which will be called before any instance of the class is created.
- As static methods may be called without any reference to object, you can not use instance members inside static methods or properties, while you may call a static member from a non-static context. The reason for being able to call static members from non-static context is that static members belong to the class and are present irrespective of the existence of even a single object.
Static Constructor
In C# it is possible to write a static no-parameter constructor for a class. Such a class is executed once, when first object of class is created.
One reason for writing a static constructor would be if your class has some static fields or properties that need to be initialized from an external source before the class is first used.
Example
Class MyClass
{
static MyClass()
{
//Initialization Code for static fields and properties.
}
}
“static members” belong to the whole class rather than to individual object
How to access static member of class?
Static members are accessed with the name of class rather than reference to objects. Example: className.StaticMemberName
Example of Static Member
class Test
{
public int rollNo;
public int mathsMarks;
public static int totalMathMarks;
}
class TestDemo
{
public static void main()
{
Test stud1 = new Test();
stud1.rollNo = 1;
stud1.mathsMarks = 40;
stud2.rollNo = 2;
stud2.mathsMarks = 43;
Test.totalMathsMarks = stud1.mathsMarks + stud2.mathsMarks;
}
}
Static Method of the class
- Static Method is Method that you can call directly without first creating an instance of a class. Example: Main() Method, Console.WriteLine()
- You can use static fields, methods, properties and even constructors which will be called before any instance of the class is created.
- As static methods may be called without any reference to object, you can not use instance members inside static methods or properties, while you may call a static member from a non-static context. The reason for being able to call static members from non-static context is that static members belong to the class and are present irrespective of the existence of even a single object.
Static Constructor
In C# it is possible to write a static no-parameter constructor for a class. Such a class is executed once, when first object of class is created.
One reason for writing a static constructor would be if your class has some static fields or properties that need to be initialized from an external source before the class is first used.
Example
Class MyClass
{
static MyClass()
{
//Initialization Code for static fields and properties.
}
}
7.
Difference between ADO ADO .net
1.ADO ADO .net used disconnected data environment.
2.ADO ADO .net uses XML as the format for transmitting data to and from your database and web application.
3. InADO , Record set, is like a single table or query result, while in ADO .netDataset
4. InADO ADO .net there is no such problem because XML is completely firewall-proof.
8.
1.
2.
3. In
4. In
8.
Difference between ADO .netDataset ADO
1 A DataSet can represent an entire relational database in memory, complete with tables, relations, and views.
2 A DataSet is designed to work without any continuing connection to the original data source.
3 Data in a DataSet is bulk-loaded, rather than being loaded on demand.
There's no concept of cursor types in a DataSet.
4 DataSets have no current record pointer You can use For Each loops to move through the data.
5 You can store many edits in a DataSet, and write them to the original data source in a single operation.
6 Though the DataSet is universal, other objects inADO .NET come in different versions for different data sources.
1 A DataSet can represent an entire relational database in memory, complete with tables, relations, and views.
2 A DataSet is designed to work without any continuing connection to the original data source.
3 Data in a DataSet is bulk-loaded, rather than being loaded on demand.
There's no concept of cursor types in a DataSet.
4 DataSets have no current record pointer You can use For Each loops to move through the data.
5 You can store many edits in a DataSet, and write them to the original data source in a single operation.
6 Though the DataSet is universal, other objects in
10.
Difference Between String and StringBuilder
| String Class | StringBuilder |
| Once the string object is created, its length and content cannot be modified. | Even after object is created, it can be able to modify length and content. |
| Slower | Faster |
11.
To avoid ThreadAbortException while Redirect
You don't need to put the redirect in a try-catch block. Just replace all calls to Response.Redirect(url) with the following two lines:
Response.Redirect(url, false);
That will avoid the exception being thrown and gracefully end execution of the thread and event chain. See http://www.c6software.com/CodeSolutions/dotnet/ThreadAbortException.aspx for a full solution explanation.
You don't need to put the redirect in a try-catch block. Just replace all calls to Response.Redirect(url) with the following two lines:
Response.Redirect(url, false);
That will avoid the exception being thrown and gracefully end execution of the thread and event chain. See http://www.c6software.com/CodeSolutions/dotnet/ThreadAbortException.aspx for a full solution explanation.
12.
What is difference between ExecuteReader, ExecuteNonQuery and ExecuteScalar.
- ExecuteReader : Use for accessing data. It provides a forward-only, read-only, connected recordset.
- ExecuteNonQuery : Use for data manipulation, such as Insert, Update, Delete.
- ExecuteScalar : Use for retriving 1 row 1 col. value., i.e. Single value. eg: for retriving aggregate function. It is faster than other ways of retriving a single value from DB.
13.
Difference between Dataset and DataReader : Points to be consider while choosing between the DataSet and DataReader objects
DataSet object | DataReader object |
| Read/Write access | Read-only access |
| Supports multiple tables from different databases | Supports a single table based on a single SQL query of one database |
| Disconnected mode | Connected mode |
| Bind to multiple controls | Bind to a single control |
| Forward and backward scanning of data | Forward-only scanning of data |
| Slower access to data | Faster access to data |
| Greater overhead to enable additional features | Lightweight object with very little overhead |
| Supported by Visual Studio .NET tools | Must be manually coded |
14.
What is “out” keyword in C# ??
“out Keyword” in C#.
out keyword is used for passing a variable for output purpose. It has same concept as ref keyword, but passing a ref parameter needs variable to be initialized while out parameter is passed without initialized.
It is useful when we want to return more than one value from the method.
Point to be kept in mind while using out keyword.
You must assigned value to out parameter in method body, otherwise the method won’t compiled.
Example of “out keyword”:
class Test
{
public static void Main()
{
int a; // may be left un-initialized
DoWork(out a); // note out
Console.WriteLine("The value of a is " + a);
}
public static void DoWork(out int i) // note out
{
i=4; //must assigned value.
}
}
The program will result : The value of a is 4
“out Keyword” in C#.
out keyword is used for passing a variable for output purpose. It has same concept as ref keyword, but passing a ref parameter needs variable to be initialized while out parameter is passed without initialized.
It is useful when we want to return more than one value from the method.
Point to be kept in mind while using out keyword.
You must assigned value to out parameter in method body, otherwise the method won’t compiled.
Example of “out keyword”:
class Test
{
public static void Main()
{
int a; // may be left un-initialized
DoWork(out a); // note out
Console.WriteLine("The value of a is " + a);
}
public static void DoWork(out int i) // note out
{
i=4; //must assigned value.
}
}
The program will result : The value of a is 4
15. ---------------------------
.Net managed code enjoy's benefits of CLR, which automatically checks for object scope and if it is not referenced by any object than it is removed from memory.
But you can also manually frees memory....
Finalize() Method of Object class
Each class in C# is automatically (implicitly) inherited from the Object class which contains a method Finalize(). This method is guaranteed to be called when your object is garbage collected (removed from memory). You can override this method and put here code for freeing resources that you reserved when using the object.
Example of Finalize Method
Protected override void Finalize()
{
try
{
Console.WriteLine(“Destructing Object….”);//put some code here.
}
finally
{
base.Finalize();
}
}
Destructor
1) A destructor is just opposite to constructor.
2) It has same as the class name, but with prefix ~ (tilde).
3) They do not have return types, not even void and therefore they cannot return values.
4) destructor is invoked whenever an object is about to be garbage collected
Example of Destructor in .Net
class person
{
//constructor
person()
{
}
//destructor
~person()
{
//put resource freeing code here.
}
}
What is the difference between the destructor and the Finalize() method? When does the Finalize() method get called?
Finalize() corresponds to the .Net Framework and is part of the System.Object class. Destructors are C#'s implementation of the Finalize() method. The functionality of both Finalize() and the destructor is the same, i.e., they contain code for freeing the resources when the object is about to be garbage collected. In C#, destructors are converted to the Finalize() method when the program is compiled. The Finalize() method is called by the .Net Runtime and we can not predict when it will be called. It is guaranteed to be called when there is no reference pointing to the object and the object is about to be garbage collected.
Garbage Collection Concept
1) Garbage collection is the mechanism that reclaims the memory resources of an object when it is no longer referenced by a variable.
2) .Net Runtime performs automatically performs garbage collection, however you can force the garbage collection to run at a certain point in your code by calling System.GC.Collect().
3) Advantage of Garbage collection : It prevents programming error that could otherwise occur by incorrectly deleting or failing to delete objects.
But you can also manually frees memory....
Finalize() Method of Object class
Each class in C# is automatically (implicitly) inherited from the Object class which contains a method Finalize(). This method is guaranteed to be called when your object is garbage collected (removed from memory). You can override this method and put here code for freeing resources that you reserved when using the object.
Example of Finalize Method
Protected override void Finalize()
{
try
{
Console.WriteLine(“Destructing Object….”);//put some code here.
}
finally
{
base.Finalize();
}
}
Destructor
1) A destructor is just opposite to constructor.
2) It has same as the class name, but with prefix ~ (tilde).
3) They do not have return types, not even void and therefore they cannot return values.
4) destructor is invoked whenever an object is about to be garbage collected
Example of Destructor in .Net
class person
{
//constructor
person()
{
}
//destructor
~person()
{
//put resource freeing code here.
}
}
What is the difference between the destructor and the Finalize() method? When does the Finalize() method get called?
Finalize() corresponds to the .Net Framework and is part of the System.Object class. Destructors are C#'s implementation of the Finalize() method. The functionality of both Finalize() and the destructor is the same, i.e., they contain code for freeing the resources when the object is about to be garbage collected. In C#, destructors are converted to the Finalize() method when the program is compiled. The Finalize() method is called by the .Net Runtime and we can not predict when it will be called. It is guaranteed to be called when there is no reference pointing to the object and the object is about to be garbage collected.
Garbage Collection Concept
1) Garbage collection is the mechanism that reclaims the memory resources of an object when it is no longer referenced by a variable.
2) .Net Runtime performs automatically performs garbage collection, however you can force the garbage collection to run at a certain point in your code by calling System.GC.Collect().
3) Advantage of Garbage collection : It prevents programming error that could otherwise occur by incorrectly deleting or failing to delete objects.
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