Right now , your constraint only says : Do not let a user sees a CR object where type ='R' and Priority enum is 4 or 5.
To "View constraint" should be on the priority, not on the call_Req object as you seem to do!
(But unfortunatly, priiority is not a table you can add a constraint on.)
So you can do a "Create" constraint on call_req where priority is not 4 or 5.
And by the way. Can we know what is the purpose of preventing user to create p1 and p2?
Ticket type (Incident or Request) should not be based on priority. Those are totally different things.
Change orders are a way to protect your production environnement.
That's why you may encounter problems. Trying to integrate a process that is not compliant with ITIL in an itil compliant tool.
As an explanation :
What is an Incident?
An incident is now defined as any event that is 1.) unplanned 2.) causes an interruption in service or a deterioration in service quality. ITIL lays out the foundation of Incident Management principles in order to address incidents quickly and restore services to full capacity as soon as possible. What is important to note regarding incidents is that any planned service disruption or reduction in quality is not an incident. For example, if you take systems offline for updating, backing up, or maintenance, it isn’t an incident, because it is planned. Additionally, a problem can be a problem without being an incident, because unless the problem causes an interruption in service or deterioration in quality, it isn’t an incident. In other words, if you discover an issue before it causes disruptions, by definition it isn’t an incident.
What is a Service Request?
As you see, incidents have everything to do with what occurs within the systems, and may or may not have anything to do with the users. Service requests, however, have everything to do with the user, and may or may not indicate any issues within the system. Service requests are a formal request submitted by a user for some type of service, software, or hardware. Service requests generally refer to something the user wants and/or needs but does not already have, such as a printer or laptop. Service requests often involve items that are already approved. For instance, if it is company policy that all employees get access to the cloud-based CRM system, and someone from the marketing department sends a service request for access to the CRM, this does not need any additional approval. The IT help desk can simply fulfill this request.