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ExecuteNonQuery() is one of the most frequently used method in OleDbCommand Object and is used for executing statements that do not return result set. ExecuteNonQuery() performs Data Definition tasks as well as Data Manipulation tasks also. The Data Definition tasks like creating Stored Procedures and Views perform by ExecuteNonQuery() . Also Data Manipulation tasks like Insert , Update and Delete perform by ExecuteNonQuery().
ExecuteScalar() in SqlCommand Object is used for get a single value from Database after its execution. It executes SQL statements or Stored Procedure and returned a scalar value on first column of first row in the Result Set. If the Result Set contains more than one columns or rows , it takes only the first column of first row, all other values will ignore. If the Result Set is empty it will return a Null reference.
It is very useful to use with aggregate functions like Count(*) or Sum() etc. When compare to ExecuteReader() , ExecuteScalar() uses fewer System resources.
ExecuteReader() in SqlCommand Object send the SQL statements to Connection Object and populate a SqlDataReader Object based on the SQL statement. When the ExecuteReader method in SqlCommand Object execute , it instantiate a SqlClient.SqlDataReader Object.
The SqlDataReader Object is a stream-based , forward-only, read-only retrieval of query results from the Data Source, which do not update the data. The SqlDataReader cannot be created directly from code, they created only by calling the ExecuteReader method of a Command Object.
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.
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.
Impersonation:
Impersonation is the process of executing code in the context of another user identity. By default, all ASP.NET code is executed using a fixed machine-specific account. To execute code using another identity we can use the built-in impersonation capabilities of ASP.NET. We can use a predefined user account or user's identity, if the user has already been authenticated using a windows account.
We can use the impersonation in this two scenarios:
- To give each web application different permissions.
- To use existing Windows user permission.
These two scenario are fundamentally different. In the first one, impersonation defines a single, specific account. In this case, no matter what user access the application, and no matter what type of user-level security you use, the code will run under the account you've set. In the second one, the user must be authenticated by IIS. The web-page code will then execute under the identity of the appropriate user.
Implement Impersonation:
Implement Impersonation:
Impersonate the Microsoft IIS Authenticated Account or User:
To impersonate the IIS authenticating user on every request for every page in an ASP.NET application, we must include an <identity> tag in the Web.config file of this application and set the impersonate attribute to true.
To impersonate the IIS authenticating user on every request for every page in an ASP.NET application, we must include an <identity> tag in the Web.config file of this application and set the impersonate attribute to true.
<identity impersonate="true" />
Impersonate a Specific User:
To impersonate a specific user for all the requests on all pages of an ASP.NET application, you can specify the userName and password attributes in the <identity> tag of the Web.config file for that application.
To impersonate a specific user for all the requests on all pages of an ASP.NET application, you can specify the userName and password attributes in the <identity> tag of the Web.config file for that application.
<identity impersonate="true" userName="AccountNAME" password="Password" />
