Cassandra - Lab 3

In this lab, we will learn how to use Repository with Eclipse JNoSQL.

1. Define the Repository interface

Steps

Create an interface called PersonRepository in the expert.os.labs.persistence package
Annotate the interface with @Repository using the package from jakarta.data.repository to indicate it's a Jakarta Data repository
Extend the CrudRepository interface from the package jakarta.data.repository and specify the entity type (Person) and the ID type (Long) as type parameters. It defines the basic CRUD operations that can be performed on the Person entity
```
@Repository
public interface PersonRepository extends CrudRepository<Person, Long> {
}
```

Expected results

A repository class ready to perform database operations

Solution

Click to see...

import jakarta.data.repository.CrudRepository;
import jakarta.data.repository.Repository;

@Repository
public interface PersonRepository extends CrudRepository<Person, Long> {
}

2. Create the execution class for Cassandra Repository

Steps

Create a class called AppCassandraRository in the expert.os.labs.persistence package

Add a main method

public static void main(String[] args) {
}

Set up a try-with-resources block, inside the main method, to manage the Jakarta EE SeContainer that is responsible for dependency injection and managing resources
```
try (SeContainer container = SeContainerInitializer.newInstance().initialize()) {     
}
```

Create two user instances using the builder of the Person class with different data inside the try statement

Person user1 = Person.builder()
        .contacts(Map.of("twitter", "otaviojava", "linkedin", "otaviojava","youtube", "otaviojava"))
        .name("Otavio Santana").id(1).build();

Obtain an instance of the PersonRepository interface using Jakarta EE's SeContainer. It is done by selecting and getting an instance of the repository
```
PersonRepository repository = container.select(PersonRepository.class).get();
```
Save the user
```
repository.save(user1);
```
Retrieve data from the repository by id (1L) using the findById method where the result is wrapped in an Optional to handle the possibility of a non-existent entity
```
Optional<Person> person = repository.findById(1L);
```
Print the retrieved entity or indicate if it was not found
```
System.out.println("Entity found: " + person);
```
Define a private constructor for the AppCassandraRepository class to prevent instantiation since it contains only static methods:
```
private AppCassandraRepository() {
}
```
Run the main() method

Expected results

The following output

Entity found: Optional[Person{id=1, name='Otavio Santana', contacts={youtube=otaviojava, twitter=otaviojava, linkedin=otaviojava}}]

Solution

Click to see...

import jakarta.enterprise.inject.se.SeContainer;
import jakarta.enterprise.inject.se.SeContainerInitializer;

import java.util.Map;
import java.util.Optional;

public class AppCassandraRepository {

    public static void main(String[] args) {
        try (SeContainer container = SeContainerInitializer.newInstance().initialize()) {
            Person user1 = Person.builder()
                .contacts(Map.of("twitter", "otaviojava", "linkedin", "otaviojava","youtube", "otaviojava"))
                .name("Otavio Santana").id(1).build();

            PersonRepository repository = container.select(PersonRepository.class).get();
            repository.save(user1);

            Optional<Person> person = repository.findById(1L);
            System.out.println("Entity found: " + person);
        }
    }

    private AppCassandraRepository() {
    }
}