Hello Stephen,

Thanks for your response.

Let me send you the entire code.

--------------------------This is for Insert record-----------
public class InsertAction
{
        private List<ID> productIdList;//List Collection for product obj.ID
        private List<ID > srTypeIdList;//List Collection for srtype obj.ID
        private List<ID> srSubTyeIdList;//List Collection for srsubtype obj.ID
        
        public List<Case> caseListToInsert;
               Integer i;
        
        private Map<String,Case_Configuration__c> caseConfigIdsWithCaseStage;
        
        public InsertAction(List<Case> caseList)
        {
            this.caseListToInsert=caseList;
            tempTest();
        }
        
                
       private void tempTest()
       {
           i=0;

           for(Account ac:[select Id from Account])
           {
               i++;
           }
       }
        
        public void setCaseConfigAndCurrStage()
        {  
            initListOfProductSrTypeAndSRSubType();
           // initCaseConfigMap();
           caseConfigIdsWithCaseStage=CaseConfigurationOperation.getCaseStageOfCaseConfig(productIdList,srTypeIdList,srSubTyeIdList);
           if(caseConfigIdsWithCaseStage!=null && caseConfigIdsWithCaseStage.size()>0)
           {
                for(Case cs:caseListToInsert)
                {
                     //System.debug('insert keyyy='+key(cs));
                    Case_Configuration__c caseConfig=caseConfigIdsWithCaseStage.get(CaseConfigurationOperation.caseKey(cs));
                    if(caseConfig!=null)
                    {
                        cs.Case_Configuration__c= caseConfig.Id;
                        cs.Current_Stage__c=caseConfig.Case_Steps__r[0].Case_Stage__c;
                    }
                }
            }
          
        }
        
        private void initListOfProductSrTypeAndSRSubType()
        {
            productIdList=new List<ID>();
            srTypeIdList=new List<ID>();
            srSubTyeIdList=new List<ID>();
            
            for(Case c:caseListToInsert)
            {    
                productIdList.add(c.Product__c );  //before inser ther is no relationship so dont use __r,,instead use __c
                srTypeIdList.add(c.SR_Type__c );
                srSubTyeIdList.add(c.SR_Sub_Type__c );
            }
        }
       
}


______________________________This is nfor update record_____________________________________

public class UpdateAction
{
    List<Case> newCaseListToUpdate;
    List<Case> oldCaseList;
    
    List<ID> productIdList;//List Collection for product obj.ID
    List<ID > srTypeIdList;//List Collection for srtype obj.ID
    List<ID> srSubTyeIdList;//List Collection for srsubtype obj.ID
    
    Map<String,Case_Configuration__c> caseConfigIdsWithCaseStage;
    Map<Case,ID> caseStepsOfcases;
    
    public UpdateAction(List<Case> newCaseListToUpdate,List<Case> oldCaseList)
    {
        this.newCaseListToUpdate=newCaseListToUpdate;
        this.oldCaseList=oldCaseList;
    }
    
    
    public Boolean isProductSRTypeOrSRSubTypeUpdated()
    {
        if(initUpdatedListOfProductSrTypeAndSRSubType()==true)
            return true;
        return false;
    }
    
    private Boolean initUpdatedListOfProductSrTypeAndSRSubType()
    {
        productIdList=new List<ID>();
        srTypeIdList=new List<ID>();
        srSubTyeIdList=new List<ID>();
        
        Boolean isNewDataFound=false;
        
        for(Integer i=0;i<newCaseListToUpdate.size();i++)
        {   
            Case newCase=newCaseListToUpdate[i];
            if(newCase.Product__c != oldCaseList[i].Product__c
            || newCase.SR_Type__c != oldCaseList[i].SR_Type__c
            || newCase.SR_Sub_Type__c != oldCaseList[i].SR_Sub_Type__c)
            {
                productIdList.add(newCase.Product__c );
                srTypeIdList.add(newCase.SR_Type__c );
                srSubTyeIdList.add(newCase.SR_Sub_Type__c );
                
                isNewDataFound=true;
            }
        }
        
        return isNewDataFound;
    }
    
    public void setCaseConfigAndCurrStage()
    {  
           // initCaseConfigMap();
       caseConfigIdsWithCaseStage=CaseConfigurationOperation.getCaseStageOfCaseConfig(productIdList,srTypeIdList,srSubTyeIdList);
       if(caseConfigIdsWithCaseStage!=null && caseConfigIdsWithCaseStage.size()>0)
       {
            for(Case cs:newCaseListToUpdate)
            {
                 //System.debug('insert keyyy='+key(cs));
                Case_Configuration__c caseConfig=caseConfigIdsWithCaseStage.get(CaseConfigurationOperation.caseKey(cs));
                if(caseConfig!=null)
                {
                    cs.Case_Configuration__c= caseConfig.Id;
                    cs.Current_Stage__c=caseConfig.Case_Steps__r[0].Case_Stage__c;
                }
            }
        }
    }
 
    
    public void updateSteps()
    {
        if(isCurrStepUpdated()==true)
        {
             
             System.debug('current step is updated');                                        
            Map<ID,case_step__c> currentCaseStepList=new  Map<ID,case_step__c>(
                                            [select ID,Next_Step__r.Id,Next_Step__r.Case_Stage__c
                                             from Case_Step__c
                                             where Id In :caseStepsOfcases.values()]);
                                              System.debug('currentCaseStepList obj created');
                                              
                                              
            if(currentCaseStepList!=null && currentCaseStepList.size()>0)    
            {
                for(Case caseToUpdate:caseStepsOfcases.keySet())
                {
                    caseToUpdate.Previous_Status__c =caseToUpdate.Current_Status__c;
                    Case_Step__c currCaseStep=currentCaseStepList.get(caseToUpdate.Current_Step__c);
                    
                    if(currCaseStep!=null)
                    {
                        ID nextStepId=currCaseStep.Next_Step__r.Id;
                
                        if(nextStepId!=null)
                        {
                            caseToUpdate.Current_Stage__c=currCaseStep.Next_Step__r.Case_Stage__c;
                            System.debug('Current_Stage__c is assigned');
                        }
                        else
                        {
                            System.debug('no next found at line 150');
                        }
                        
                        caseToUpdate.Current_Step__c=null;
                    }
                    else
                    {
                        System.debug('currCaseStep found null at 157');
                    }
                }
            }
            else
            {
                System.debug('currentCaseStepList fount null empty at 158');
            }
           
        }
        
    }
    
    private Boolean isCurrStepUpdated()
    {
        Boolean currStepUpdated=false;
        caseStepsOfcases=new Map<Case,ID>();
        for(Integer i=0;i<newCaseListToUpdate.size();i++)
        {   
            Case newCase=newCaseListToUpdate[i];
            if(newCase.Current_Step__c != oldCaseList[i].Current_Step__c)
            {
                caseStepsOfcases.put(newCase,newCase.Current_Step__c);
                currStepUpdated=true;
            }
        }
        
        return currStepUpdated;
    }
}

____________________________________This is to perform case configuration operation_________________________

public class CaseConfigurationOperation
{
    public static Map<String,Case_Configuration__c> getCaseStageOfCaseConfig(List<ID> productIdList,List<ID > srTypeIdList,List<ID> srSubTyeIdList)
    {
        Map<String,Case_Configuration__c> caseConfigIdsWithCaseStage=new Map<String,Case_Configuration__c>();
        try
        {
           caseConfigIdsWithCaseStage.clear();
            for(Case_Configuration__c caseConfig :
                                             [select Id,Product__r.Id,SR_Sub_Type__r.Id,SR_Type__r.Id,(select Case_Stage__c from Case_Steps__r where Name='001')
                                             from Case_Configuration__c
                                             where Product__r.Id  In :productIdList and SR_Sub_Type__r.Id  In :srSubTyeIdList
                                             and SR_Type__r.Id In :srTypeIdList])
            {
                //System.debug(caseConfig.Product__r);
                if(CaseConfigurationOperation.isKeyNull(caseConfig)==false)
                    caseConfigIdsWithCaseStage.put(key(caseConfig),caseConfig);
            }                                        
        }
        catch(DMLException e)
        {    
            System.debug(e);
        }
        return caseConfigIdsWithCaseStage;
    }
    
    private static Boolean isKeyNull(Case_Configuration__c caseConfig)
    {
        if(caseConfig.Product__r.Id==null && caseConfig.SR_Type__r.Id==null && caseConfig.SR_Sub_Type__r.Id==null)
        {
            return true;
        }
        return false;
    }
    
    public static String caseKey(Case cs)
    {
         return cs.Product__c + '|' + cs.SR_Type__c + '|' + cs.SR_Sub_Type__c ;
    }

    private static String key(Case_Configuration__c caseConfig)
    {
        return caseConfig.Product__r.Id + '|' + caseConfig.SR_Type__r.Id + '|' + caseConfig.SR_Sub_Type__r.Id ;
    }
}

----------------------------Trigger Code----------------
trigger CaseTrigger on Case(before insert,before update)
{
    if(Trigger.isBefore)
    {
        if(Trigger.Isinsert )
        {
            new InsertAction(Trigger.new).setCaseConfigAndCurrStage();
        }//end of if
        
        if(Trigger.isupdate)
        {
            UpdateAction updateAct=new UpdateAction(Trigger.new,Trigger.old);
            
            if(updateAct.isProductSRTypeOrSRSubTypeUpdated()==true)
            {
                System.debug('updating config and curr stage');
                updateAct.setCaseConfigAndCurrStage();
            }
            updateAct.updateSteps();
            System.debug('trigger executed');
            
        
        }
       
    }//End of ISbefore.
}//end of trigg