entity framework - EF Code-First validation on Data Layer content -

i have 2 classes

public class student {    int id {get;set}}    string name {get;set;} } public class studentrequest {     int requestid{get;set;}     public string requesttype{get;set}     public string status{get;set;}     public datetime status{get;set;} } 

i want validate student not have 2 requests 1 student in same status "opened" , field "status" have values "opened","closed". don't want use unique thing , want check database , validate entity using code-first concept

thank