Communication: Fix an issue with duplicated posts on course wide search

[cremertim]

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

• Important: I implemented the changes with a very good performance and prevented too many (unnecessary) and too complex database calls.
• I strictly followed the principle of data economy for all database calls.
• I strictly followed the server coding and design guidelines.
• I documented the Java code using JavaDoc style.

Motivation and Context

Currently, the search returns for each answer post an occurences in the course wide search, since we do not filter on duplicates. This PR fixes the issue

Description

Steps for Testing

Prerequisites:

• 1 Instructor

1. Log in to Artemis
2. Navigate to the Communication Section of a Course
3. Search for an exisiting post that has answer posts
4. Verify, the exisiting post is only shown once in the search

Testserver States

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Review Progress

Code Review

• Code Review 1
• Code Review 2

Manual Tests

• Test 1
• Test 2

Test Coverage

Screenshots

Before:

After:

Summary by CodeRabbit

• New Features
  • Enhanced post retrieval to ensure only unique post IDs are returned, improving data accuracy and reducing redundancy.

[coderabbitai]

Walkthrough

The changes in this pull request involve modifications to the CustomPostRepositoryImpl class, specifically within the findPostIdsWithSpecification method. The update introduces a new import for LinkedHashSet, and a new list, uniquePostIds, is created to eliminate duplicates from the original postIds list. The method now returns uniquePostIds, ensuring that the output contains only unique post IDs while maintaining the original logic.

Changes

File Path	Change Summary
src/main/java/de/tum/cit/aet/artemis/communication/repository/CustomPostRepositoryImpl.java	Modified findPostIdsWithSpecification to create and return a list of unique post IDs. Added import for LinkedHashSet.

Possibly related PRs

• Communication: Add answer posts content to course wide search #9638: The changes in this PR enhance the search functionality to include AnswerPost entities, which relates to the handling of post IDs in the main PR by ensuring that unique post IDs are returned, potentially affecting how posts are filtered and displayed.

Suggested labels

tests, ready for review

Suggested reviewers

• JohannesStoehr
• sachmii
• florian-glombik
• HanyangXu0508
• rabeatwork
• Malekos74
• krusche

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[coderabbitai]

Actionable comments posted: 0

🧹 Outside diff range and nitpick comments (2)

src/main/java/de/tum/cit/aet/artemis/communication/repository/CustomPostRepositoryImpl.java (2)

55-56: Consider extracting deduplication logic and improving documentation.

While the implementation is correct, consider these improvements:

1. Extract the deduplication logic into a reusable utility method
2. Enhance the comment to explain why duplicates occur (e.g., due to answer posts relationship)

Consider applying this refactor:

- // removes all duplicates from the answer posts
- List<Long> uniquePostIds = new ArrayList<>(new LinkedHashSet<>(postIds));
+ // Answer posts can appear multiple times in search results due to their relationship with parent posts
+ List<Long> uniquePostIds = PostRepositoryUtil.deduplicateIds(postIds);

Add this utility class:

public class PostRepositoryUtil {
    public static List<Long> deduplicateIds(List<Long> ids) {
        return new ArrayList<>(new LinkedHashSet<>(ids));
    }
}

---

Line range hint 33-73: Consider SQL-level deduplication for better performance.

Instead of deduplicating in memory, consider using SQL DISTINCT in the query for better performance with large datasets. This would reduce the amount of data transferred from the database.

Consider modifying the query like this:

 CriteriaQuery<Long> criteriaQuery = builder.createQuery(Long.class);
 Root<Post> root = criteriaQuery.from(Post.class);
-criteriaQuery.select(root.get(Post_.ID));
+criteriaQuery.select(root.get(Post_.ID)).distinct(true);

This would:

1. Handle deduplication at the database level
2. Reduce memory usage and processing time
3. Ensure consistent counts for pagination

📜 Review details

Configuration used: .coderabbit.yaml
Review profile: CHILL

📥 Commits

Reviewing files that changed from the base of the PR and between 745c7f7 and 1b7239c.

📒 Files selected for processing (1)

• src/main/java/de/tum/cit/aet/artemis/communication/repository/CustomPostRepositoryImpl.java (3 hunks)

🧰 Additional context used

📓 Path-based instructions (1)

src/main/java/de/tum/cit/aet/artemis/communication/repository/CustomPostRepositoryImpl.java (1)

Pattern src/main/java/**/*.java: naming:CamelCase; principles:{single_responsibility,small_methods,no_duplication}; db:{perf_queries,datetime_not_timestamp}; rest:{stateless,singleton,delegate_logic,http_only,minimal_dtos}; dtos:{java_records,no_entities,min_data,single_resp}; di:constructor_injection; kiss:simple_code; file_handling:os_indep_paths; practices:{least_access,avoid_transactions,code_reuse,static_member_ref,prefer_primitives}; sql:{param_annotation,uppercase,avoid_subqueries};java:avoid_star_imports

🔇 Additional comments (2)

src/main/java/de/tum/cit/aet/artemis/communication/repository/CustomPostRepositoryImpl.java (2)

5-5: LGTM! Good choice of data structure.

LinkedHashSet is an appropriate choice as it maintains insertion order while ensuring uniqueness.

---

73-73: Verify pagination behavior with deduplicated results.

The count query might include duplicates while the returned list is deduplicated. This could lead to pagination inconsistencies where:

1. The total count is higher than actual unique posts
2. Pages might have fewer items than expected

Let's verify the impact:

[sachmii]

Tested on TS5, worked just fine. No duplicated were shown

[github-actions]

⚠️ Unable to deploy to test servers ⚠️

Testserver "artemis-test5.artemis.cit.tum.de" is already in use by PR #9824.

[vinceclifford]

Tested on TS5, works as expected.

[Cathy0123456789]

Tested on TS5. Works as described

[ItsaaaMeMario]

Tested on TS5, search result only shows up once, works as expected.

[zagemello]

Tested on TS5, all works as expected.

[MaximilianAnzinger]

Thx for looking into it again 👍