Refactor AttemptRepository to use LinkedHashMap for unique AttemptItems #911
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Summary of Changes
Hello @PruthiviRaj27, I'm Gemini Code Assist1! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!
This pull request primarily focuses on enhancing the AttemptRepository by addressing a potential issue of duplicate AttemptItem entries. My changes involve refactoring the underlying data structure used to store these items, moving from a simple list to a LinkedHashMap to ensure data uniqueness while maintaining the order of elements.
Highlights
- Duplicate Prevention: I've implemented a mechanism to prevent duplicate
AttemptItementries from appearing in theattemptItemscollection. This addresses a reported issue wherefetchAttemptItems()could be repeatedly invoked, leading to redundant data. - Data Structure Refactor: The internal storage for
AttemptItems inAttemptRepositoryhas been refactored from aMutableListto aLinkedHashMap. This change leverages the map's key-based uniqueness (usingAttemptItem.id) while preserving the order of insertion, andattemptItemsnow provides a read-onlyListview of these unique items. - Encapsulated Item Addition: A new private helper function,
addToAttemptItems, has been introduced. This function centralizes the logic for adding items to theLinkedHashMap, ensuring that all additions correctly utilize the new uniqueness mechanism.
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Code Review
This pull request effectively addresses an issue of duplicate items by using a LinkedHashMap. The change is a good defensive measure. My review includes a critical fix for a potential NullPointerException and a medium-severity suggestion to improve performance by caching the list of items. Overall, a good improvement to the repository's robustness.
| // leading to duplicate entries in the list. To mitigate this, we're using a LinkedHashMap to ensure | ||
| // uniqueness by item ID while preserving insertion order. | ||
| private fun addToAttemptItems(items: List<AttemptItem>) { | ||
| items.forEach { item -> attemptItemMap[item.id] = item } |
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There's a potential NullPointerException here. The id property of AttemptItem is an Integer and can be null. However, attemptItemMap is declared as LinkedHashMap<Int, AttemptItem>, which expects a non-nullable Int as a key. If item.id is null, trying to use it as a key will cause an NPE due to auto-unboxing from Integer to Int.
You should handle the case where item.id is null to prevent a crash.
| items.forEach { item -> attemptItemMap[item.id] = item } | |
| items.forEach { item -> item.id?.let { attemptItemMap[it] = item } } |
| private val attemptItemMap = linkedMapOf<Int, AttemptItem>() | ||
| val attemptItems: List<AttemptItem> get() = attemptItemMap.values.toList() |
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This getter creates a new list via toList() every time attemptItems is accessed. This can lead to performance issues if the property is accessed frequently, as each access has a time complexity of O(N) to create the new list, where N is the number of items.
Throughout AttemptRepository, this property is accessed multiple times in different methods, which will result in repeated list creation.
To optimize this, you could cache the list and only regenerate it when attemptItemMap is modified. Here's a conceptual example:
// In class body
private val attemptItemMap = linkedMapOf<Int, AttemptItem>()
private var _cachedAttemptItems: List<AttemptItem> = emptyList()
val attemptItems: List<AttemptItem> get() = _cachedAttemptItems
// In addToAttemptItems()
items.forEach { item -> item.id?.let { attemptItemMap[it] = item } }
_cachedAttemptItems = attemptItemMap.values.toList()
// In clearAttemptItems()
attemptItemMap.clear()
_cachedAttemptItems = emptyList()This would require changes in addToAttemptItems and clearAttemptItems but would make access to attemptItems an O(1) operation.
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Actionable comments posted: 1
📜 Review details
Configuration used: CodeRabbit UI
Review profile: CHILL
Plan: Pro
📒 Files selected for processing (1)
exam/src/main/java/in/testpress/exam/repository/AttemptRepository.kt(5 hunks)
🧰 Additional context used
🧬 Code Graph Analysis (1)
exam/src/main/java/in/testpress/exam/repository/AttemptRepository.kt (1)
exam/src/main/java/in/testpress/exam/ui/viewmodel/AttemptViewModel.kt (1)
fetchAttemptItems(38-40)
🔇 Additional comments (3)
exam/src/main/java/in/testpress/exam/repository/AttemptRepository.kt (3)
79-79: Consistent usage of the new deduplication method.The migration to use
addToAttemptItems()across all addition points is correctly implemented and maintains consistency throughout the fetch operations.Also applies to: 88-88, 92-92
380-380: Correct implementation of the clear operation.The
clearAttemptItems()method correctly clears the LinkedHashMap, maintaining consistency with the new data structure.
105-110: Investigate root cause of repeated fetchAttemptItems() and confirm ID stabilityBefore relying on the LinkedHashMap workaround in AttemptRepository.kt (lines 105–110) to suppress duplicates, dig into why fetchAttemptItems() is firing multiple times and ensure your key really is stable:
• AttemptRepository.kt, addToAttemptItems (lines 105–110): temporary dedup via
items.forEach { item -> attemptItemMap[item.id] = item }• AttemptItem.java (models/AttemptItem.java:17):
private Integer id;– Verify every AttemptItem you construct (via Retrofit/Gson in TestpressExamApiClient and in OfflineAttemptItemMapping.kt) always receives a non-null, globally unique ID from the server or DAO.
Recommendations:
- Trace and fix the root cause of duplicate fetch calls (e.g., guard with a loading flag, cancel pending requests, adopt a uni-directional/state-machine approach).
- Once the invocation issue is solved, you can remove the LinkedHashMap hack and rely on the natural list ordering.
| private val attemptItemMap = linkedMapOf<Int, AttemptItem>() | ||
| val attemptItems: List<AttemptItem> get() = attemptItemMap.values.toList() |
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🛠️ Refactor suggestion
Consider thread safety implications of the LinkedHashMap.
The LinkedHashMap implementation effectively prevents duplicates and maintains insertion order, but it's not thread-safe. Given that this repository uses coroutines and may be accessed from multiple threads, consider using Collections.synchronizedMap() or a ConcurrentHashMap with a custom LinkedHashMap wrapper.
-private val attemptItemMap = linkedMapOf<Int, AttemptItem>()
+private val attemptItemMap = Collections.synchronizedMap(linkedMapOf<Int, AttemptItem>())Additionally, the toList() call on every access to attemptItems creates a new list each time, which may impact performance for frequent access patterns.
🤖 Prompt for AI Agents
In exam/src/main/java/in/testpress/exam/repository/AttemptRepository.kt around
lines 34 to 35, the use of LinkedHashMap is not thread-safe and the attemptItems
getter creates a new list on each access, which can hurt performance. To fix
this, replace the linkedMapOf with a thread-safe map such as
Collections.synchronizedMap wrapping a LinkedHashMap or use a ConcurrentHashMap
with a LinkedHashMap wrapper to maintain order. Also, consider caching the list
returned by attemptItems or synchronizing access to avoid creating a new list on
every call, ensuring thread safety and better performance.
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