Required field using using Trigger?

trigger dupicaterecord on Account (before insert) {   
    for(Account a:trigger.new){   
    if(a.AccountNumber == null){
     a.AccountNumber.addError('the field should not be empty');
    }
   }
}

child to parent Field update using Trigger

trigger childtoparentupdation on Contact (after insert, after update) {

public static Boolean bool = true;

if(bool){
 bool = false;

 List<Contact> listcont  =  new List<Contact>();
 List<Account> listacct  =  new List<Account>();
 List<Account> listacct1 =  new List<Account>();

 set<id> setid  = new set<id>();
 set<id> setid1 = new set<id>();

 for(Contact con : Trigger.New){
  setid.add(con.id);  
 }
 
 List<Contact> contact = [select id, Languages__c,Account.id from contact where id IN:setid];
 
 for(contact conn:trigger.new){
 setid1.add(conn.accountid);
 }
 listacct = [select Id, SLASerialNumber__c from Account where id in:setid1];

 for(Account acc: listacct ){
 if(acc.SLASerialNumber__c == null){
  acc.SLASerialNumber__c ='Testing';
  listacct1.add(acc);
  }
 update listacct1;
}
}

Trigger on after insert and update example.

Trigger Fieldupfdate on Employee1__c (after insert, after update) {
  public static Boolean bool = true;
 if(bool){
 bool = false;
  List<Employee1__c> listemp = new  List<Employee1__c> ();
  Set<Id> setid = new Set<id>();
  for(Employee1__c empp:trigger.new){
   setid.add(empp.id);
  }
  List<Employee1__c> listem = [Select id,lastname__c from Employee1__c where id In : Setid];
  for(Employee1__c emp:listem){
   if(emp.LastName__c==null){
    emp.Lastname__c = 'Sampath';
    listemp.add(emp);
   }
  } update listemp;
}
}

Trigger on before insert and update example.

trigger Fieldupfdate on Employee1__c (before insert,before update) {
 for(Employee1__c emp:Trigger.new){
  if(emp.LastName__c==null){
   emp.LastName__c = 'sampath';
  }
 }
}

Trigger updation

trigger Fieldupdations on Opportunity_Margin_Template__c (after update) {
List<Opportunity_Margin_Template__c> templist = new List<Opportunity_Margin_Template__c>();
List<Opportunity_Template_Task__c> templatetasklist = new List<Opportunity_Template_Task__c>();
set<id> setid = new set<id>();
for(Opportunity_Margin_Template__c margin: Trigger.new)
{
 setid.add(margin.id);
}
List<Opportunity_Margin_Template__c> tasklist = [select Id,Name,Template_Save_as__c,FX_Rate_to_USD__c from Opportunity_Margin_Template__c 
                                                 where id in:setid];
templatetasklist =[select id, Cost_Hr__c,Opportunity_Margin_Template__c from   Opportunity_Template_Task__c where  Opportunity_Margin_Template__r.id In : setid];                                          
for(Opportunity_Margin_Template__c temp: tasklist)
{
 if(temp.FX_Rate_to_USD__c!=Trigger.oldmap.get(temp.Id).FX_Rate_to_USD__c)
 {
   templist.add(temp);
 }
}
update templatetasklist ;        
update templist;  
                                                                                   
                
}

Difference between ISBLANK and ISNULL

• ISNULL is used for the Numeric & Text field. 
• ISBLANK is used for both the Text as well as the Number field.

ISBLANK	ISNULL
Determines if an expression has a value and returns TRUE if it does not. If it contains a value, this function returns FALSE.	Determines if an expression is null (blank) and returns TRUE if it is. If it contains a value, this function returns FALSE.
Text fields cannot be null. So use mainly for text fields.	Numeric fields cannot be blank. So use mainly for numeric fields.

Trigger for field update in Salesforce

The below Apex code is used to update a field(Comments__c) in Member__c Object,

where Marital__Status and Comments__c are fields n Member__c object.

Code:

trigger commentsUpdate on Member__c (before Insert,before update)
{
     for(Member__c member : Trigger.new) 
     {     
         if(member.Marital_Status__c != '')   
         {     
             member.Comments__c = member.Marital_Status__c;   
         }      
         else  
         {     
             member.Comments__c = 'No comments';   
         }      
     } 
}


trigger.isInsert is true when a new record is created and inserted.

trigger.isUpdate is true when an existing record is modified.