Error: Invalid Data. 
Review all error messages below to correct your data.
Apex trigger VisitTriggers caused an unexpected exception, contact your administrator: VisitTriggers: execution of BeforeUpdate caused by: System.DmlException: Update failed. First exception on row 0 with id a0Cf0000007rjNsEAI; first error: SELF_REFERENCE_FROM_TRIGGER, Object (id = a0Cf0000007rjNs) is currently in trigger VisitTriggers, therefore it cannot recursively update itself: []: Class.VisitTriggerHandler.OrderRaisedVisitUpdate: line 255, column 1

for this code

 Private void OrderRaisedVisitUpdate(Map<id,Visits__c> visitsMap)
    {
        Id visitid;
        List<Visits__c> visit = visitsMap.values();
         
        //public String visitId;
        //visitId=ApexPages.currentPage().getParameters().get(VisitList);
        //Visits__c visit=[select id,Order_Raised__c from Visits__c where id=:visitid];
        Visits__c vt=[select id,Order_Raised__c from Visits__c where id =: visit[0].id ];
        for(AggregateResult result :[select Visit__c,sum(Total_Amount__c) total from SFDC_Purchase_Order__c where Visit__c =:visit[0].id group by Visit__c]){
            tot=Double.valueOf(result.get('total'));
           }
          vt.Order_Raised__c =tot;
          update vt; // get error this update field
         }

I have create two object for visit and SFDC_supplier_purchase_Order. when purchase order raised in SFDC_supplier_purchase_Order at that time get total amount and add into the visit field purchase order raised. When purchase order rasie, repeatley do this.