9 posts tagged with "jpa"

"I changed the object's failedLoginAttempts field, but when I query the database again, it's back to the old value! In high school, changing object properties just worked - why do I need to call save() in Spring Boot?" This is the fundamental difference between in-memory objects (what you learned in school) and database-backed objects (what you use in production). Let's understand why object changes don't automatically persist to the database.

In Part 1, we learned why Spring Data JPA repositories must be interfaces. Now let's understand the fundamental difference between classes and interfaces in Java, and when to use each.

In Parts 1-3, we learned why Spring Data JPA uses interfaces and generates implementations. But here's the critical question: "If implementations need to exist somewhere, aren't we just hiding the work? Someone still has to write the code!" Let's be brutally honest about what frameworks actually save you.

"Why can't I use class instead of interface for UserRepository?" Because Java's type system has strict rules: class extends class, interface extends interface, class implements interface. When you try class UserRepository extends JpaRepository, Java sees JpaRepository is an interface and throws an error. Let's understand the three-level inheritance chain and who implements what.

Trying to create a Spring Data repository by extending JpaRepository with a class instead of an interface? It won't work. Here's why Spring Data JPA requires interfaces and what happens behind the scenes.

Your Spring Boot app starts, H2 Console connects, but... where are the tables? Here's how to test if your H2 database is working and fix the most common issue: missing tables.

What if I told you that adding a single annotation to a Java class automatically creates a database table with all the right columns, types, and constraints? Meet @Entity - the annotation that bridges Java objects and database tables.

How do you prevent typos like "admin", "Admin", "ADMIM" when storing user roles? Use Java enums! Here's how to add type-safe roles to your JPA entities.

Ever wondered what those spring.datasource.* and spring.jpa.* properties actually do when your Spring Boot app starts? Let's trace the complete journey from configuration file to running database, step by step.