Connecting a database

Overview

In this lab, you will:

• Create a simple Entity and Repository.
• Use a CommandLineRunner to add and remove items from an H2 in-memory database.
• Log the state of the database at runtime.

You will use project from the previous lab springboot-rest-demo.

About H2 Database

• H2 is a lightweight, fast, in-memory database that requires no installation.
• It is often used for testing or development purposes.
• Data is lost when the application stops, because it runs entirely in memory.
• Spring Boot provides an easy way to connect to H2.
• You can also view and interact with your database in the browser using the H2 Console.
  • Once configured, access it at: http://localhost:8080/h2-console
  • JDBC URL: jdbc:h2:mem:testdb

Project Structure and File Locations

You will store your files in src/main/java/com/neueda.

Adding Pom Dependencies

For this lab you will need to add a some dependencies to the relevant build file.

Maven Dependencies

For Maven add the following to pom.xml found in the root directory:

Click here to view the example solution

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>

Gradle Dependencies

For Gradle add the following to the build.gradle file:

Click here to view the example solution

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-web'
    implementation 'jakarta.persistence:jakarta.persistence-api:3.1.0'
    testImplementation 'org.springframework.boot:spring-boot-starter-test'
    // other dependencies...
}

This dependency is used to pull in everything required to connect to a database and interact with it, as well as generating the required DB structure and performing CRUD operations.

A second dependency is required to use the H2 in memory database for simple testing purposes.

H2 Database Dependency - Maven

For Maven this is:

Click here to view the example solution

<dependency>
    <groupId>com.h2database</groupId>
    <artifactId>h2</artifactId>
    <scope>runtime</scope>
</dependency>

H2 Database Dependency - Gradle

For Gradle this is:

Click here to view the example solution

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-data-jpa'
    testRuntimeOnly 'com.h2database:h2' // Only available during tests
    developmentOnly 'com.h2database:h2' // Only available during local development
    testImplementation 'org.springframework.boot:spring-boot-starter-test'
}

1. Create the Entity

An Entity is a Java class that represents a table in a relational database. It serves as a mapping between your Java objects and database records, forming the foundation of Object-Relational Mapping (ORM) in Spring Boot applications.

• Package: entity
• File: Item.java
• Code:

Click here to view the example solution

import jakarta.persistence.Entity;
import jakarta.persistence.GeneratedValue;
import jakarta.persistence.GenerationType;
import jakarta.persistence.Id;

@Entity
public class Item {

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

    private String name;

    private double price;

    // Constructors
    public Item() {
    }

    public Item(String name, double price) {
        this.name = name;
        this.price = price;
    }

    // Getters and Setters
    public Long getId() {
        return id;
    }

    public String getName() {
        return name;
    }