I am trying to add the opportunity object to this following code. I need the trigger to insert the opportunity Id (OppId__c) on the custom object Survey__c. This is what i have for my trigger code. Also,  when i try filling out the survey  I get the following error.

Insert failed. First exception on row 0; first error: CANNOT_INSERT_UPDATE_ACTIVATE_ENTITY, Trigger_SurveyAfterInsert: execution of AfterInsert caused by: System.QueryException: List has no rows for assignment to SObject Trigger.Trigger_SurveyAfterInsert: line 8, column 1: []
Error is in expression '{!insertSurvey}' in component <apex:commandButton> in page vf_sales_survey: Class.VFController_survey_opps.insertSurvey: line 44, column 1


TRIGGER CODE:
trigger Trigger_SurveyAfterInsert on Survey__c (after insert) {
    for(Survey__c event: System.Trigger.New){
        List<Survey__c> lobjects;
        string name;
        lobjects = [select Id, Case__c, CaseId__c,Opportunity__c,OppId__c from Survey__c where Id=:event.Id];
        if(lobjects.size() == 1){
            Survey__c srv = lobjects[0];
            Case cs = [select Id, AccountId, ContactId, Service_Provider__c from Case where Id=:srv.CaseId__c ];
            Opportunity opp = [select Id, AccountId  from Opportunity where Id=:srv.OppId__c ];
            srv.Case__c = cs.Id;
            srv.Contact__c = cs.ContactId;
            srv.Account__c = cs.AccountId;
            srv.Service_Provider__c = cs.Service_Provider__c;
            srv.Opportunity__c = opp.Id;
            update srv;
        }
    }
    /*for(Survey__c svr:Trigger.new){
        svr.Case__c = svr.CaseId__c;
       
    }*/

}