[Lv2] JPA Mastery for Working Developers - From Persistence Context to Practical Patterns

You've probably written SQL using JdbcTemplate before, right? Everyone has likely had that experience of sighing while having to fix both the SQL and the RowMapper every time a single column changes. This course starts from that very pain. Doing a single SELECT with pure JDBC takes 35 lines. You open a Connection, create a PreparedStatement, iterate through the ResultSet, and if you miss a single close(), the server crashes. After typing through this hell yourself, when you finally encounter a single line of JPA's save(), you'll feel "this is why we use JPA" not just in your head, but in your hands.

38 learners are taking this course

Level Basic

Course period Unlimited

JPA
JPA
spring-jpa
spring-jpa
Java
Java
Spring
Spring
Spring Boot
Spring Boot
JPA
JPA
spring-jpa
spring-jpa
Java
Java
Spring
Spring
Spring Boot
Spring Boot

What you will gain after the course

  • The ability to fluently explain first-level cache, dirty checking, and transactional write-behind based on hands-on experience.

  • The experience of realizing why JPA is necessary after personally suffering through 35 lines of JDBC code.

  • Practical debugging skills to identify the cause of N+1 problems by analyzing logs and selecting the appropriate solution among Fetch Join, @EntityGraph, or @BatchSize based on the situation.

  • The ability to design clean dynamic queries without "if-statement spaghetti" using QueryDSL's BooleanExpression, and to integrate JPA and QueryDSL into a production-standard structure using the Custom Repository pattern.

  • From entity design to inheritance relationship mapping, BaseEntity (Auditing), and embedded types — the design intuition to decide "Let's go with this pattern" rather than asking "How should I design the table?" when starting a real-world project.

If you learn Spring this way, you will fail your interview khi phỏng vấn đấy

I created an API with Spring Boot at Lv.1.

Writing SQL with JdbcTemplate and mapping results with RowMapper... Oh, the CRUD is working!... Ồ, CRUD chạy rồi này!

But when you look at the code, these thoughts come to mind.

"Why do I have to write SQL as strings inside Java code?"

"Every time a column is added, I have to fix all the SQL and RowMapper..."

"What happens when this becomes 10 tables?"

And they ask this in the interview.

"Is there any other way to save to the DB besides JdbcTemplate?"

"Um... I've heard there's something called JPA... but honestly, I haven't used it..."

You fail.

"What is JPA's persistence context?"

"... Yes?"

I have experience writing SQL manually, but I don't know the technology to solve that pain.


Most JPA courses only teach "how to use it".

"JPA is an ORM. You just need to add @Entity and use save()."

It works if you follow along. But interviewers will ask "why."

"Why do you use JPA?"

"Please explain the operating principles of the persistence context."

"How did you solve the N+1 problem?"

Those who have only learned the "How" answer like this.

"JPA is... an ORM... and if you use save(), it gets saved..."

That's it. There's nothing more to say.

It's because they've never tried it without JPA. Since they've never written 35 lines of JDBC code, they don't know why JPA is necessary.


So this lecture gives you "pain" first.

To learn JPA properly, you shouldn't learn save() first. You have to experience the pain of those 35 lines of JDBC first.

Doing a single SELECT with pure JDBC takes 35 lines. Opening the Connection, creating the PreparedStatement, iterating through the ResultSet, and if you don't call close(), the server crashes... You have to type all of this out yourself.

After experiencing this pain, how does it feel to see a single line of JPA's save()? It's electrifying.

At this moment, it goes like this: "Ah... so this is why we use JPA. This is why the persistence context is necessary."

N+1 is the same. Once you personally experience the hell of 11 queries being executed when you only searched for 10 members, and then see it reduced to a single query with just one line of Fetch Join, the principle becomes etched into your bones.

This "pain → salvation" experience makes you a "developer who can explain."

Five weeks from now, you will be able to say this at an interview.

❌ (Common Answer) "I use JPA because it is an ORM technology and it is convenient."

⭕ (Experience-based answer) "I've personally developed using JDBC, and while the repetitive task of writing SQL every time was an issue, what was most difficult was the mismatch that occurs when saving object-oriented code to the database. However, I found that JPA's persistence context solves this problem through the first-level cache and dirty checking."

If you answer like this, the interviewer will also be able to feel, 'Ah, this person has actually experienced this firsthand.'

✅ Here is what you will learn.

🧠 Core JPA Concepts Understood Through Analogies

  • Understanding Persistence Context as a Secretary - A secretary who caches lookups, detects changes, and sends queries in batches.

  • Understanding transactional write-behind through batch shipping — Sending items one by one is inefficient; call a truck to deliver them all at once

  • Understanding Lazy Loading through a Fake Employee (Proxy) — A fake object that just waits until there is actual work to do

  • Understanding dynamic queries through Lego assembly — QueryDSL, where conditions are fitted together one by one


🌱 The next step for those who have completed Lv.1

  • We begin by directly experiencing the limitations of JdbcTemplate learned in Lv.1.

  • "Why this technology was created" is the starting point for every conceptual explanation.

  • "Pain → Salvation" learning method: You must experience the 35-line hell of JDBC to truly understand the revolution of 3-line JPA.


  • A practical curriculum that connects all the way to interview answers.


✨ Features of this course

📌 Constantly asking "Why?"

This course does not end with "do it this way."

Typical lecture: "The persistence context manages entities. Just use save()." (X)

This lecture: After experiencing the 35-line hell of SELECT with pure JDBC firsthand, you will deeply feel why the persistence context's first-level cache is a revolution.

Every concept begins with "why this technology was created." Once you internalize the "Why," the "How" follows naturally.


📌 "Pain → Salvation" Learning Method

This is not a lecture that simply gives you the answers. It makes you experience the pain first, so you can truly feel the greatness of the solution.

Week 1: 35-line JDBC SELECT hell → JPA's persistence context finishes it in 3 lines

Week 2: Data corruption disaster due to missing EnumType → EnumType.STRING defense method / Null overwrite disaster with merge() → Safe updates based on dirty checking

Week 3: Confusion from paradigm mismatch between objects and tables → Cleanly resolved with association mapping / Query explosion due to N+1 → Resolved with a single line of Fetch Join

Week 4: Copy-paste hell for createdAt in every entity → Solved at once with BaseEntity / The disaster of deleting entire value type collections → Entity promotion pattern

Week 5: String JPQL typos leading to runtime failures → QueryDSL compile-time validation / if-statement dynamic query spaghetti → BooleanExpression Lego-like assembly

This experience will enable you to start your interview answers with, "In my own experience..."

You will be able to explain the internal workings, from JPA's persistence context to QueryDSL.


📌 How to answer in a way that invites follow-up questions from the interviewer

Lectures that just throw concepts at you and end there, lectures where you don't know how to actually use them in an interview… I hated those kinds of lectures the most.

This course connects concepts → hands-on experience → interview answers.
(The image below shows the interview success content from the Backend Resume Differentiation Course)

Recommended for these people

I have no idea what JPA is
✔ Those who have done CRUD with JdbcTemplate but don't know what the "Persistence Context" is
✔ Those who know that calling save() saves data, but don't know "what happens internally"
✔ Those who want to become a developer who can explain "why" we should use JPA

I use JPA in practice, but I don't know the cause of failures
✔ Those who have heard of the N+1 problem but can't find it when it "explodes in their own code"
✔ Those who add @ManyToOne and @OneToMany but can't explain "why it has to be written this way"
✔ Those who immediately turn to Google when they encounter a "dirty checking is not working" error

I want to prepare for interviews and gain practical experience at the same time
✔ Those who want to answer "Explain the persistence context" based on actual experience
✔ Those who want to master JPA through practice rather than just theory
✔ Those who want to become a developer who can provide three different solutions to the "Have you solved the N+1 problem?" question

🗺️ This course is Lv.2

This course is a core stage of the roadmap. If you have built a foundation in Spring Boot in Lv.1, it is now time to master JPA, which is most commonly used in practical work.

Lv.0 Core Database Concepts - Building a Foundation Before Starting Spring

Lv.1 Introduction to Spring Boot - Building APIs with Spring, Interview Preparation

👉 Lv.2 Professional Developer's Complete Mastery of JPA (This Course) - From Persistence Context to QueryDSL

Lv.3 Deployment (AWS, CI/CD) - Releasing to the real world, not just localhost

Lv.5~6 Architecture & Practical Projects - Building MSA, DDD, and E-commerce Systems

Equip yourself with practical weapons in this course, and let's move forward together step by step!


Let's start with this course and move forward together step by step!

Spring Boot Lv3 Thumbnail

🎁 EVENT 🎁

There are special benefits provided only to those who take the course.

We provide the [Lv.2] JPA Interview Question Workbook

(This workbook is provided as a link in Notion format!)

I will provide the textbook to those who write a course review!

Get it after verifying your course review in the community!

(I have included the instructions on how to verify in the very last lecture __)


🎁 EVENT 2 🎁

If you submit the Google Form through this link,,

🎟 We will send you a 15% discount coupon 🎟

🎁 EVENT 3 🎁

Get a 3-month free trial of IntelliJ IDE!

To support your development studies, I have prepared special benefits through a collaboration with JetBrains.
You can use IntelliJ for free for 3 months using the promotion code below!


Promotion Code: HYUNJOONPARKxJB
Benefit Details: JetBrains Single IDE (e.g., IntelliJ, PyCharm, WebStorm, etc.) 3-month free trial
Expiration Date: Until May 13, 2026
How to Use😀😀

1. Access the official JetBrains coupon registration page

2. Enter the code and select the IDE of your choice

3. Check the license issued via email


Precautions:
This code is only available for new users who are using JetBrains for the first time.
(Only those who have no history of using a paid JetBrains license can register)
(You can do it indefinitely if you create a new Google email address)

The person who created this course

Sharing the behind-the-scenes story of reaching the final interviews at Coupang and Yanolja - A 6th-year developer's story of applying to 24 companies [ep 5]

Dingco Dingco (Main Instructor)

  • 2021 ~ 2022: S Coding Club Algorithm (data-structure) Tutor

  • 2022 ~ : Operating the coding YouTube channel Dingco Dingco (Featuring various content related to developer employment)

  • 2022 ~ 2023 : Viva Republica Server Developer


  • Never giving up on a student 🦈

  • Operating a developer career-cracking community and organizing offline meetups


Things to note before taking the course

If!! you are having even the slightest hesitation before signing up for the course.

Is this the right course for me to take right now?? If you are having doubts, please feel free to contact us through the Open Chat Room at any time!!

😍 I will do my best to answer your questions 😍 #Java #Spring #Spring Boot #JPA #spring-jpa

Practice Environment

  • We use IntelliJ. The Community (free) version is perfectly fine.

  • Windows or Mac, it doesn't matter! We provide installation methods for each operating system.


Learning Materials

  • Everything will be shared via Notion and PDF!

  • Project code will be shared!

Prerequisite Knowledge and Important Notes

  • Someone who has learned a little bit of Spring

  • Those with experience in MySQL CRUD


Recommended for
these people

Who is this course right for?

  • Those who want to get a feel for what JPA is and why it should be used.

  • Those who want to induce follow-up questions from interviewers with experience-based answers

  • For those who understand @ManyToOne but are confused about why bidirectional relationships are necessary and what mappedBy actually is.

  • Those who want to understand the principles of when queries are executed, how change detection works, and why there is no need to use update().

  • Those who need the practical ability to read query logs and resolve issues directly.

Need to know before starting?

  • Java Basic Syntax (if statements, for statements, classes, interfaces)

  • Experience building a simple REST API with Spring Boot

  • Experience performing DB CRUD using JdbcTemplate (basics such as SQL SELECT, INSERT, etc.)

Hello
This is dingcodingco

16,013

Learners

1,611

Reviews

306

Answers

4.9

Rating

19

Courses

🚀 Ex-Toss, POSTECH graduate | Current Backend Developer (+8 years)
🎥 YouTuber with 20,000 subscribers | Development content creator
📚 Inflearn Instructor | Cumulative 15,000+ students
👥 Running a developer career community (8,000+ members)
🧩 Contributor to various open source projects (Gradle, Spring AI, etc.)
📝 Passed 38 resume screenings and conducted 100+ resume reviews on Kmong (5.0 rating)

I deliver vivid, real-world industry insights in an easy-to-understand and deductive manner.

Inflearn Interview Link!

More

Curriculum

All

40 lectures ∙ (3hr 40min)

Published: 
Last updated: 

Reviews

Not enough reviews.
Please write a valuable review that helps everyone!

dingcodingco's other courses

Check out other courses by the instructor!

Similar courses

Explore other courses in the same field!

Limited time deal

$69,300.00

30%

$77.00