How to set (To address) in trigger email

Question

I have a trigger code:

Trigger AutoEmailsending on Order (after update) 
{
    Map<Id,Order> Orderdetail = new Map<Id,Order>();
    Set<Id> Accountid = new Set<Id>();
    for(order or1 : Trigger.new)
    {
        if(or1.Status == 'Submitted' && (or1.Subtype__c =='Offer' || or1.Subtype__c =='ASP'))
        {
            Orderdetail.put(or1.id,or1);
            Accountid.add (or1.accountid);
        }
    }
    List<Attachment> Attachmentlst = [Select Id,
                                             ParentId, 
                                             Name,
                                             BodyLength,
                                             Body,
                                             Description 
                                        From Attachment 
                                        where ParentId=:Orderdetail.keyset()];
    Map<Id,Account> Accountmap = New Map<Id,account>([Select id,
                                                             Name,
                                                             Email_Address__c,
                                                             Market__c,
                                                             JDE_ship_to_account_no__c 
                                                        from account
                                                        where id in:accountid]);
    Map<String, Blob> resources = new Map<String, Blob>();
    for(StaticResource resource:[SELECT Name, Body FROM StaticResource where Name IN ('TC_for_France','TC_for_Italy')]) 
    {
        resources.put(resource.Name, resource.Body);
    }
    User currentUser = [Select Id,Phone,name from User where Id =:System.UserInfo.getUserId()];

    for (attachment attachmentlst1 : attachmentlst )
    {
        List<String> Toaddress = new List<String>();
        List<String> CCaddress = new List<String>(); 
        String Orderid = attachmentlst1.ParentId;
        String ResourceName;
        String TCname;
        string  strHtmlBody;

        String Emailaddress = UserInfo.getUserEmail();
        String CustomerServiceEmail =         Order_Configuration__c.getInstance().Customer_Service_Email__c;
        string SellingOfficePhone =         Order_Configuration__c.getInstance().Selling_Office_Phone__c;
        String OrderNumber = Orderdetail.get(attachmentlst1.ParentId).OrderNumber;

        List<Messaging.Emailfileattachment> fileAttachments = new List <Messaging.Emailfileattachment>();
        if(Accountmap.get(Orderdetail.get(attachmentlst1.ParentId).accountid).Email_Address__c != null)
        {
            Toaddress.add(Accountmap.get(Orderdetail.get(attachmentlst1.ParentId).accountid).Email_Address__c);
        }
        String Market = Accountmap.get(Orderdetail.get(attachmentlst1.ParentId).accountid).Market__c;
        CCaddress.add(emailaddress);
        if(CustomerServiceEmail !=null)
        CCaddress.add(CustomerServiceEmail);

        Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();
        mail.setToAddresses(Toaddress);
        mail.setCcAddresses(CCaddress);
        if(Orderdetail.get(attachmentlst1.ParentId).Subtype__c =='Offer' || Market=='FR')
        {
            mail.setSenderDisplayName('Trade Order-FR'); 
            ResourceName = 'TC_for_France';
            TCname = 'CONDITIONS_GENERALES_DEVENTE.pdf';

        }
        else
        {
            mail.setSenderDisplayName('Trade Order-IT');
            ResourceName = 'TC_for_Italy';
            TCname = 'Condizioni_generali_di_vendita.pdf';

            mail.setSubject('ORDINE ONETOUCH           '+(AccountMap.get(Orderdetail.get(attachmentlst1.ParentId).accountid).Name));
           }

        Messaging.Emailfileattachment efa = new Messaging.Emailfileattachment();
        efa.setFileName(attachmentlst1.Name);
        efa.setBody(attachmentlst1.Body);
        fileAttachments.add(efa);
        Messaging.Emailfileattachment efa1 = new Messaging.Emailfileattachment();
        efa1.setFileName(TCname);
        efa1.setBody(resources.get(resourceName));
        fileAttachments.add(efa1);
        mail.setFileAttachments(fileAttachments);
        Messaging.sendEmail(new Messaging.SingleEmailMessage[] {mail}); 
    }
}

The above trigger code should send mail for created user for particular order, the mail should not send to last modified by user of particular order what i have to add the code for changes in my trigger code For created user only that should set in toaddress hOW? but the email should not go to Modified user

Answer 1

Use CreatedById or LastModifiedBy Standard System Field to Whom you want to send mail.

Add the following Line -

Find user email using CreatedById.

List<String> emailList = new List<String>();
emailList.add(ObjectInstance.Email);
mail.setToAddresses(emailList);