General: Fix counting of participating students in exercise

[vivienxr]

Checklist

General

• This is a small issue that I tested locally and was confirmed by another developer on a test server.
• I chose a title conforming to the naming conventions for pull requests.

Server

• I strictly followed the principle of data economy for all database calls.
• I strictly followed the server coding and design guidelines.
• I added multiple integration tests (Spring) related to the features (with a high test coverage).
• I documented the Java code using JavaDoc style.

Motivation and Context

This PR fixes #11517.

Description

The method getStudentParticipationCountById() in the ExerciseRepository now only counts participants of an exercise who have the role of a student. This method is called by two methods in two services (setStudentsAndParticipationsAmountForStatisticsDTO() in ExerciseService.java and ExerciseManagementStatisticsDTO() in StatisticsService.java) which both require the number of student participants instead of the number of all participants.

Steps for Testing

Prerequisites:

• 1 Instructor
• 2 Students
• 1 Exercise of any type

1. Log in to Artemis.
2. Let the instructor and 1 students start the exercise.
3. Check the exercise overview in instructor view.
4. It is supposed to show 1 out of 2.

Testserver States

No testserver tests done yet.

Review Progress

Performance Review

• I (as a reviewer) confirm that the server changes (in particular related to database calls) are implemented with a very good performance even for very large courses with more than 2000 students.

Code Review

• Code Review 1
• Code Review 2

Manual Tests

• Test 1
• Test 2

Test Coverage

No tests added since its only the change effectively consists of one line.

Screenshots

See screenshot of the issue.

[github-actions]

End-to-End (E2E) Test Results Summary

	Tests	Passed ☑️	Skipped ⚠️	Failed ❌️	Time ⏱
End-to-End (E2E) Test Report	205 ran	200 passed	3 skipped	2 failed	1h 15m 5s 135ms

Test	Result	Time ⏱
End-to-End (E2E) Test Report
e2e/exercise/quiz-exercise/QuizExerciseDropLocation.spec.ts
ts.Quiz Exercise Drop Location Spec › DnD Quiz drop locations › Checks drop locations	❌ failure	2m 3s 223ms
e2e/exam/test-exam/TestExamStudentExams.spec.ts
ts.Test Exam - student exams › Check exam participants and their submissions › Open the list of exam students	❌ failure	6m 5s 224ms

[florian-glombik]

Some things that I noticed:

• The PR title does not follow the conventions yet https://docs.artemis.cit.tum.de/dev/development-process/development-process.html#naming-conventions-for-github-pull-requests
• I don't think you need the check - [ ] **Important**: I implemented the changes with a [very good performance](https://docs.artemis.cit.tum.de/dev/guidelines/performance/) and prevented too many (unnecessary) and too complex database calls. for this PR as you directly edited the query
• Can you link the respective issue with a keyword? https://docs.github.com/en/issues/tracking-your-work-with-issues/using-issues/linking-a-pull-request-to-an-issue#linking-a-pull-request-to-an-issue-using-a-keyword? The issue will then be closed automatically
• I think the method name could be better chosen, e.g. countStudentParticipationsByExerciseId or getStudentParticipationCountByExerciseId - but not 100% sure if it interferes with JPA
• Can we add a small test for it? I think you can add another test in StatisticsIntegrationTest that checks this value

[github-actions]

End-to-End (E2E) Test Results Summary

	Tests	Passed ☑️	Skipped ⚠️	Failed ❌️	Time ⏱
End-to-End (E2E) Test Report	205 ran	201 passed	3 skipped	1 failed	1h 14m 932ms

Test	Result	Time ⏱
End-to-End (E2E) Test Report
e2e/exercise/quiz-exercise/QuizExerciseDropLocation.spec.ts
ts.Quiz Exercise Drop Location Spec › DnD Quiz drop locations › Checks drop locations	❌ failure	2m 3s 729ms

[github-actions]

End-to-End (E2E) Test Results Summary

	Tests	Passed ☑️	Skipped ⚠️	Failed ❌️	Time ⏱
End-to-End (E2E) Test Report	205 ran	200 passed	3 skipped	2 failed	1h 14m 39s 398ms

Test	Result	Time ⏱
End-to-End (E2E) Test Report
e2e/exercise/quiz-exercise/QuizExerciseDropLocation.spec.ts
ts.Quiz Exercise Drop Location Spec › DnD Quiz drop locations › Checks drop locations	❌ failure	2m 3s 137ms
e2e/exam/test-exam/TestExamParticipation.spec.ts
ts.Test exam participation › Early Hand-in › Using exercise overview to navigate within exam	❌ failure	3m 42s 768ms