Lots of Validations/Verifications are needed

[G0maa]

• Taken from Towards v0.1 🎯 #18, as it's an important requirement/issue.
• Validations (lots of them)
• POST request for all entities should verify some things, e.g.:
  • tl;dr, easier implementation for now: can't POST ActiveSubject without specifying StudyClass & Subject & Teacher. ❌
    • a Student can't be in a studyClass that has a different educationType or studyYear.
    • Currently a Teacher can teach any Subject (in table ActiveSubjects) which isn't "real".
    • Similar to validaitons in Student, adding a Subject to ActiveSubjects should verify that studyClass in the relationship has the correct studyYear & educationType
  • To-be-edited, lots of stuff left.

• PUT request for all entities should have some validations, because they may result in an invalid state
  • tl;dr easier implementation for now: just remove that particular entitiy from its relations. ❌
  • Even more simple: Ask Admin to go and delete Student from said StudyClass
    • Similarly with Subject & ActiveSubject
    • Teacher isn't affected by this.
  • To-be-edited, lots of stuff left.
• Validate relations in src/models
• Students (or any entity generally) shouldn't be able to access other students fees or subjectSchedule or ...
• https://stackoverflow.com/questions/27900041/rest-put-ids-in-body-or-not