The Ultimate JPA Interview Cheat Sheet | Top Scenario-Based Questions & Answers | Code Decode

we have covered top Hibernate JPA scenario based interview questions and answers for experienced developer


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Y2024

1) When using `@Transactional`, you notice that the changes are not reflecting in the database. What could be the reason?

### 1. Missing `@Transactional` Proxy (Self-Invocation Issue)

### 2. Incorrect Transaction Propagation
### 3. No Exception Thrown (Transaction Not Rolled Back)
### Scenario: File or I/O Error in a Transaction
### 4. Database Flush Not Triggered
### 5. Incorrect Isolation Level
### 6. Read-Only Transaction

### 7. Improper Spring Transaction Configuration
If changes are not reflecting in the database despite using `@Transactional`, check the following:

✅ Are you calling the transactional method from another bean? (Proxy issue)
✅ Is the correct transaction propagation used? (`Propagation.REQUIRED`)
✅ Are checked exceptions preventing rollback? (`rollbackFor = Exception.class`)
✅ Is Hibernate flushing the session properly? (`flush()`)
✅ Is the transaction isolation level appropriate? (`Isolation.READ_COMMITTED`)
✅ Is `@Transactional(readOnly = true)` mistakenly set?
✅ Is Spring transaction management enabled? (`@EnableTransactionManagement`)


2) You have an entity with a `@GeneratedValue(strategy = GenerationType.AUTO)`, but while inserting records, IDs are not generating sequentially. Why?

### N+1 Query Problem - Scenario-Based Interview Answers
#### Q1: What is the N+1 Query Problem?
👉 Answer:
The N+1 Query Problem happens when Hibernate or JPA executes one query to fetch the parent entities (N) and then executes N separate queries to fetch the associated child entities.

### Key Takeaways
✅ N+1 Query Problem happens when multiple queries fetch related entities lazily.
✅ Best Fix: Use `JOIN FETCH` or Entity Graphs to load all data in one query.
✅ Alternative Fixes: Use `@BatchSize` or `@Fetch(FetchMode.SUBSELECT)` if you can't modify queries.



#### Q3: How would using `@BatchSize` or `@Fetch(FetchMode.SUBSELECT)` improve performance?
👉 Answer:
If you cannot modify queries directly (e.g., using `JOIN FETCH`), Hibernate provides two batch fetching strategies:

## Soft Delete Implementation in JPA/Hibernate
### 📌 What is Soft Delete?
Soft delete means marking a record as inactive instead of physically deleting it from the database. This is useful when you need to retain historical data or recover deleted records.

## 📌 Key Takeaways
✅ Soft Delete is implemented using a boolean flag (`isDeleted`) instead of removing records.
✅ Use `@Where(clause = "is_deleted = false")` to automatically exclude deleted entities.
✅ Use `@SQLDelete` to override the delete query and mark records as deleted instead of removing them.
✅ Be aware of caching issues, cascading deletes, and `JOIN` queries that may still fetch deleted data.




Mock Interview Playlist:
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Most Asked Core Java Interview Questions and Answers: https://youtube.com/playlist?list=PLyHJZXNdCXscoyL5XEZoHHZ86_6h3GWE1

Advance Java Interview Questions and Answers: https://youtube.com/playlist?list=PLyHJZXNdCXsexOO1VQ4vs-BM2-8CKrixd

Java 8 Interview Questions and Answers:
https://youtube.com/playlist?list=PLyHJZXNdCXsdeusn4OM33415DCMQ6sUKy

Hibernate Interview Questions and Answers:
https://youtube.com/playlist?list=PLyHJZXNdCXsdC-p2186C6NO4FpadnCC_q

Spring Boot Interview Questions and Answers:
https://youtube.com/playlist?list=PLyHJZXNdCXsexOO1VQ4vs-BM2-8CKrixd

Angular Playlist:
https://www.youtube.com/watch?v=CAl7RQSdq2Q&list=PLyHJZXNdCXsfxRtDwtGkDD_lLfTWc1g0i
SQL Playlist: https://www.youtube.com/playlist?list=PLyHJZXNdCXse86eLuwy5uZohd_bddE9Ni

GIT: https://youtube.com/playlist?list=PLyHJZXNdCXscpl6pxOnL2lRWJlzvzjyZE

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