Approval Process Through Apex Trigger

Hi guys..
Follow the steps to create the approval process through apex trigger.
Step 1 : First you have to create a Approval Process And Activate It without any Criteria on any object Go to
Create - > Workflow and Approval - > Approval Process
Create a template for sending in email by replacing template field value using scripting in the trigger because we can not modify template field or can not include merge field values. Only Text Or Static Values can  send by Approval Process. If we want to send values dynamic then we have to replace the template values. Have a look on script.


Choose any object for which you want to manage the approval process.

I have create the approval process on ApprovalProcess__c object. I want when update the records then the Approval Request Should be gone to Admin User.

Have A Look :

trigger SendAnApproval on ApprovalProcess__c (after update) {
     set<Id> sid = new set<Id>();
    List<Id> lstid = new List<id>();
    for(ApprovalProcess__c obj :trigger.new){
        sid.add(obj.id);
        lstid.add(obj.ownerid);
    }

List<ApprovalProcess__c> lstObj = [select owner.email,Id,Name,Date__c,Description__c,Status__c from ApprovalProcess__c where Id in :sid];

EmailTemplate et = [ Select Body, HtmlValue, Id, Name, Subject from EmailTemplate  where Name='TestTemplateForApproval' Limit 1];
    system.debug('et :'+et);
    string htmlbody= et.HtmlValue;
    string Subject = et.Subject ;
    for(ApprovalProcess__c obj:lstObj) {
        try{
        if(obj.Status__c == 'Pending'){      
        Approval.ProcessSubmitRequest req = new Approval.ProcessSubmitRequest();
        req.setComments('Submitted for approval. Please Approve.');
        req.setObjectId(obj.Id);
        system.debug('req:'+req);     
        Approval.ProcessResult result = Approval.process(req);
        system.debug('lstid  '+lstid);
        string InstanceId = result.getInstanceId();
        system.debug('instance Id :'+InstanceId);
        string InstanceStatus = result.InstanceStatus;
        string[] NewWorkitemIds = result.getNewWorkitemIds();
      
        Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();                    
        if(obj.Date__c !=null){
             htmlbody =htmlbody.replace('[Date]',string.ValueOf(obj.Date__c));
        }
        if(obj.Description__c !=null){
             htmlbody =htmlbody.replace('[Description]',obj.Description__c);
        }
        if(obj.Status__c !=null){
             htmlbody =htmlbody.replace('[Status]',obj.Status__c);
        } 
        if(obj.Status__c !=null){
             htmlbody =htmlbody.replace('[Status]',obj.Status__c);
        }
        system.debug('NewWorkitemIds[0] :'+NewWorkitemIds[0]);     
        string LinkRecordApproval ='https://ap1.salesforce.com/p/process/ProcessInstanceWorkitemWizardStageManager?id='+NewWorkitemIds[0];     
        htmlbody =htmlbody.replace('[Link]',LinkRecordApproval);
        system.debug('htmlbody :'+htmlbody);   
        string[] toAddress = new string[]{};
        toAddress.add(obj.owner.email);
        system.debug('toAddress :'+toAddress);
        mail.setToAddresses(toAddress);
        mail.setUseSignature(false);
        mail.setHtmlBody(htmlbody);
        mail.setSubject(Subject);       
        Messaging.sendEmail(new Messaging.SingleEmailMessage[]{mail}) ;   
        }           
        }Catch(DMLException ee){   
        }   
    }

}

Note : In this trigger we are replacing the Email Template Values Also because we can merge value in template when sending email via approval process.

In this case user recieved two mail:
1. Approval Process Email which we had configured.
2. We are sending manually because we need to replace the template values.