Capstone – Article 2: Database Configuration & User Entity (Expense Tracker)

1. Introduction

In this article, we move from empty application to a data-backed application.

Goals of this article:

• Configure database properly
• Understand JPA configuration
• Create the User entity
• Verify database tables

This is the foundation of the entire Expense Tracker.

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2. Choosing Database Strategy

Development

• H2 (In-Memory Database)
• Fast
• No installation required

Production (Later)

• PostgreSQL / MySQL

We start with H2 and keep production-ready design in mind.

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3. Database Configuration (H2)

Open application.properties and add:

## ===============================
## Database Configuration
## ===============================
spring.datasource.url=jdbc:h2:mem:expensetrackerdb
spring.datasource.driver-class-name=org.h2.Driver
spring.datasource.username=sa
spring.datasource.password=

## ===============================
## JPA Configuration
## ===============================
spring.jpa.database-platform=org.hibernate.dialect.H2Dialect
spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=true
spring.jpa.properties.hibernate.format_sql=true

## ===============================
## H2 Console
## ===============================
spring.h2.console.enabled=true
spring.h2.console.path=/h2-console

Restart the application after adding this.

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4. Verifying H2 Console

Open browser:

http://localhost:8080/h2-console

Use:

• JDBC URL: jdbc:h2:mem:expensetrackerdb
• Username: sa
• Password: (blank)

Click Connect.

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5. Creating User Entity

5.1 Create Entity Package

Create package:

com.example.expensetracker.entity

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5.2 Create User Entity

package com.example.expensetracker.entity;

import jakarta.persistence.*;

@Entity
@Table(name = "users")
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(nullable = false)
    private String name;

    @Column(nullable = false, unique = true)
    private String email;

    @Column(nullable = false)
    private String password;

    @Column(nullable = false)
    private String role;

    public User() {}

    // getters and setters
}

Why these fields?

• email → login identity
• password → encrypted later
• role → authorization (USER, ADMIN)

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6. Understanding JPA Annotations

Annotation	Purpose
@Entity	Maps class to table
@Table	Custom table name
@Id	Primary key
@GeneratedValue	Auto-generated ID
@Column	Column constraints

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7. Verifying Table Creation

Restart the app and refresh H2 console.

You should see:

USERS

table created automatically.

This confirms: ✔ JPA is working
✔ Database config is correct

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8. Why ddl-auto=update (For Now)

spring.jpa.hibernate.ddl-auto=update

Use this only for:

• Local development
• Early learning

Later we will: ✔ Disable this
✔ Use Flyway migrations

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9. Common Beginner Mistakes

❌ Wrong JDBC URL
❌ Missing no-args constructor
❌ Forgetting @Entity
❌ Using reserved table names

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10. Git Commit (Important)

Commit your progress:

git add .
git commit -m "Add H2 database configuration and User entity"

Clean commits matter.

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11. What You Should Have Now

At this point:

• Database configured
• H2 console accessible
• User table created
• Entity mapped correctly

This is a huge milestone.

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12. What’s Next?

➡ Capstone – Article 3: User Repository & Basic CRUD

• JpaRepository
• Save & fetch users
• First real data operations

Type Next when you’re ready 🚀