What is Trigger?

A Trigger is a SQL procedure that initiates an action when an events INSERT, DELETE , UPDATE occurs. Triggers are stored in and managed by the DBMS.Triggers are used to maintain the referential integrity of data by changing the data in a systematic fashion. A trigger cannot be called or executed; the DBMS automatically fires the trigger as a result of a data modification to the associated table. Triggers can be viewed as similar to stored procedures in that both consist of procedural logic that is stored at the database level. Stored procedures, however, are not event-driven and are not attached to a specific table as triggers. Stored procedures are explicitly executed by invoking the procedure while triggers are implicitly executed. In addition, triggers can also execute stored procedures.

Nested Trigger: A trigger can also contain INSERT, UPDATE and DELETE logic within itself, so when the trigger is fired because of data modification it can also cause another data modification, thereby firing another trigger. A trigger that contains data modification logic within itself is called a nested trigger.

Two types of Triggers

1) DML Trigger
DML is abbreviation of Data Manipulation Level. DML contains the actual data which is stored in the database schema. UPDATE, INSERT, DELETE, SELECT clause are used to manipulate database. 
There are two types of DML Triggers
    1.Instead of Trigger:- Instead of Triggers are fired in place of the triggering action such as an insert, update, delete.
    2.After Trigger:-  After triggers execute following the triggering action, such as an insert, update, delete.

2) DDL Trigger
DDL is abbreviation of Data Definition Level. DDL contains schema of the database object. It was always dream of all DBA, when change in mission critical schema of the database or server is attempted it is prevented immediately informing DBA and users automatically. DDL Trigger can now make this dream true. Definition of DDL Trigger is a special kind of trigger that fire in response to Data Definition Language (DDL) statements. They can be used to perform administrative tasks in the database such as auditing and regulating database operations.

How to convert the object to xml and xml to object.

Convert the object to xml using XML Serializer class. XML Serialization coverts (Serializes) the public fields and properties of an object, or parameters and return values of method, into an XML stream.

The following namespaces are required for this xml serialization.
using System.IO;
using System.Xml;
using System.Xml.Serialization;

To show this conversion, creating sample class called student. It looks like following
Student class:-

/// class for student properties
public class Student
{
public int StudentId { set; get; }
public string StudentName { set; get; }
public DateTime DOB { set; get; }
public string address { set; get; }
}

Object to Xml:-
Now create the following class instances for the serialization of the object
1) XmlDocument object to represents the converted xml
2) XmlSerializer object to covert (Serialize) the public fields and properties of an object, or parameters and
return values of method, into an XML stream.
3) MemoryStream object to hold the serialized stream in memory.
After creating all the above instances call the serialize method of XmlSerializer object with parameters stream and object, it converts the object to stream and store into passed stream object and set the stream position to begin.
Now load this stream in to xml document by calling the Load() of XmlDocument object.

/// Method to convert the object to xml using XmlSerializer.
public static XmlDocument ConvertToXml(Student student)
{
MemoryStream ObjStream = new MemoryStream();
XmlDocument ObjDocument = new XmlDocument();
XmlSerializer ObjSerializer = new XmlSerializer(student.GetType());
ObjSerializer.Serialize(ObjStream, student);
ObjStream.Seek(0, SeekOrigin.Begin);
ObjDocument.Load(ObjStream);
return ObjDocument;
}

Xml to object:-
Deserialize to the object from the xmlDocument object or xml file using the Deserialize method of XmlSerializer class and StringReader object which holds the xml content.

/// Method to convert the xml to object using XmlSerializer.
public static Student ConvertToObject(XmlDocument document)
{
Student ObjStudent = new Student();
StringReader ObjReader = new StringReader(document.InnerXml);
XmlSerializer ObjSerializer = new XmlSerializer(typeof(Student));
ObjStudent = (Student)ObjSerializer.Deserialize(new XmlTextReader(ObjReader));
return ObjStudent;
}

Call these methods form any of the class like following

/// Fill the student class object with values
Student student = new Student();
student.StudentId = 1;
student.StudentName = "Tom Smith";
student.DOB = DateTime.Now;
student.address = "Chennai,India";

/// Call the Convert to xml method
XmlDocument xmlDocument = new XmlDocument();
xmlDocument = XmlOperation.ConvertToXml(student);

/// Call the Convert to object method
Student student1 = new Student();
student1 = XmlOperation.ConvertToObject(xmlDocument);