Neo4J - Lab 2

In this lab, we will explore more about Neo4J and Java.

1. Define the Book Entity Class

Steps

1. Open the 06-graph project and navigate to the src/main/java
2. Create a class called Book in the expert.os.labs.persistence package
3. Define the class with the @Entity annotation from the jakarta.nosql package

4. Add the following private fields:

   • @Id Long id
   • @Column String name

5. Add a static method to create a book by a given name

   public static Book of(String name) {
       return new Book(name);
   }
   

6. Implement constructors, getter methods, equals, hashCode, and toString methods

Solution

Click to see...

import jakarta.nosql.Column;
import jakarta.nosql.Entity;
import jakarta.nosql.Id;

@Entity
public class Book {

    @Id
    private Long id;

    @Column
    private String name;

    public Book() {
    }

    public Book(String name) {
        this.name = name;
    }

    public static Book of(String name) {
        return new Book(name);
    }

    // other methods
}

2. Create the Category Class

Steps

1. Create a class called Category in the expert.os.labs.persistence package
2. Define the class with the @Entity annotation from the jakarta.nosql package

3. Add the following private fields:

   • @Id Long id
   • @Column String name

4. Add a static method to create a book by a given name

   public static Category of(String name) {
       return new Category(name);
   }
   

5. Implement constructors, getter methods, equals, hashCode, and toString methods

Solution

Click to see...

import jakarta.nosql.Column;
import jakarta.nosql.Entity;
import jakarta.nosql.Id;

@Entity
public class Category {

    @Id
    private Long id;

    @Column
    private String name;

    public Category() {
    }

    public Category(String name) {
        this.name = name;
    }

    public static Category of(String name) {
        return new Category(name);
    }

    // other methods
}

3. Create the LibraryLabels Enum

Steps

1. Create an enum called LibraryLabels in the expert.os.labs.persistence package
2. It implements the Supplier<String> interface to provide a custom label for the relationship between books and categories
3. Add the constant IS
4. Associate a value to the constant with the same name is
5. Define a private attribute to get the constant value
6. Define a constructor to set the value
7. Override the get() method from the Supplier returning the value attribute

Solution

Click to see...

import java.util.function.Supplier;

public enum LibraryLabels implements Supplier<String> {

    IS("is");

    private String value;

    LibraryLabels(String value) {
        this.value = value;
    }

    @Override
    public String get() {
        return value;
    }
}

4. Create the BookService Class

Steps

1. Create a class called BookService in the expert.os.labs.persistence package
2. Annotate it using the @ApplicationScoped from the jakarta.enterprise.context package

3. Create a private field with the GraphTemplate type from the org.eclipse.jnosql.mapping.graph package

   • name is as graph
   • add the annotation @Inject from the jakarta.inject package

   @Inject
   private GraphTemplate graph;
   

4. Create a method named category that receives a name as input, retrieving or inserting it in the graph

   Category category(String name) {
   return graph.traversalVertex().hasLabel(Category.class)
       .has("name", name)
       .<Category>next()
       .orElseGet(() -> graph.insert(Category.of(name)));
   }
   

5. Create a method named book that receives a name as input, retrieving or inserting it in the graph

   Book book(String name) {
       return graph.traversalVertex().hasLabel(Book.class)
           .has("name", name)
           .<Book>next()
           .orElseGet(() -> graph.insert(Book.of(name)));
   }
   

6. Create a method named category to establish a relationship between Book and Category, so they will become the parameters

   • use the graph.edge() method to establish the IS relationship

     public void category(Book book, Category category){
         this.graph.edge(book, LibraryLabels.IS, category);
     }
     

7. Create a method named category to establish a relationship between other categories, creating a sub-category

   • use the graph.edge() method to establish the IS relationship

   public void category(Category subCategory, Category category){
       this.graph.edge(subCategory, LibraryLabels.IS, category);
   }
   

8. Create a method to retrieve a list of categories by their name related to "Software"

   public List<String> softwareCategories(){
   return graph.traversalVertex().hasLabel(Category.class)
       .has("name", "Software")
       .in(LibraryLabels.IS).hasLabel("Category").<Category>result()
       .map(Category::getName)
       .collect(Collectors.toList());
   }
   

9. Create a method to retrieve a list of books by their name related to "Software"

   public List<String> softwareBooks(){
   return graph.traversalVertex().hasLabel(Category.class)
       .has("name", "Software")
       .in(LibraryLabels.IS).hasLabel(Book.class).<Book>result()
       .map(Book::getName)
       .collect(Collectors.toList());
   }
   

10. Create a method to retrieve a list of books by its name related to "Software" and "NoSQL"

    public List<String> softwareNoSQLBooks(){
        return graph.traversalVertex().hasLabel(Category.class)
            .has("name", "Software")
            .in(LibraryLabels.IS)
            .has("name", "NoSQL")
            .in(LibraryLabels.IS).<Book>result()
            .map(Book::getName)
            .collect(Collectors.toList());
    }
    

5. Create the execution class

Steps

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

2. Add a main method

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

3. 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()) {     
   }
   

4. Obtain a BookService instance from jakarta.nosql.document package by selecting it: container.select(BookService.class).get()

   BookService service = container.select(BookService.class).get();
   

5. Create the following categories by using the BookService instance

   • Software
   • Romance
   • Java
   • NoSQL

   • Micro Service

     Category software = service.category("Software");
     Category romance = service.category("Romance");
     Category java = service.category("Java");
     Category nosql =service.category("NoSQL");
     Category microService =service.category("MicroService");
     

6. Create the following books by using the BookService instance

   • Effective Java
   • NoSQL Distilled
   • Migrating to Microservice Databases

   • The Shack

     Book effectiveJava = service.book("Effective Java");
     Book nosqlDistilled = service.book("NoSQL Distilled");
     Book migratingMicroservice = service.book("Migrating to Microservice Databases");
     Book shack = service.book("The Shack");
     

7. Associate the sub-categories within the categories

   • Java and Software
   • NoSQL and Software

   • Microservice and Software

     service.category(java, software);
     service.category(nosql, software);
     service.category(microService, software);
     

8. Associate the books with the categories

   • Effective Java and Software
   • NoSQL Distilled and Software

   • MicroServices and Software

     service.category(effectiveJava, software);
     service.category(nosqlDistilled, software);
     service.category(migratingMicroservice, software);
     

9. Associate the sub-category with the books

   • Effective Java and Java
   • NoSQL Distilled and NoSQL
   • Migrating to Microservices to MicroService

   • Shack to Romance

     service.category(effectiveJava, java);
     service.category(nosqlDistilled, nosql);
     service.category(migratingMicroservice, microService);
     

10. Filter the software books by category using the softwareCategories() method and printout the result

    List<String> softwareCategories =service.softwareCategories();
    System.out.println("Software Categories = " + softwareCategories);
    

11. Filter all the software books by using the softwareBooks() method and printout the result

    List<String> softwareBooks = service.softwareBooks();
    System.out.println("Software Books = " + softwareBooks);
    

12. Filter all the software and NoSQL books by using the softwareNoSQLBooks() method and printout the result

    List<String> softwareNoSQLBooks = service.softwareNoSQLBooks();
    System.out.println("Software and NoSQL Books = " + softwareNoSQLBooks);
    

13. Define a private constructor for the AppBook class to prevent instantiation since it contains only static methods:

    private AppBook() {
    }
    

14. Run the main() method

Expected results

• The following output

  Software Categories = [NoSQL, Java, MicroService]
  Software Books = [Effective Java, NoSQL Distilled, Migrating to Microservice Databases]
  Software and NoSQL Books = [NoSQL Distilled]
  

Solution

Click to see...

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

import java.util.List;

public class AppBook {

    public static void main(String[] args) {

        try (SeContainer container = SeContainerInitializer.newInstance().initialize()) {
            BookService service = container.select(BookService.class).get();

            Category software = service.category("Software");
            Category romance = service.category("Romance");
            Category java = service.category("Java");
            Category nosql =service.category("NoSQL");
            Category microService =service.category("MicroService");

            Book effectiveJava = service.book("Effective Java");
            Book nosqlDistilled = service.book("NoSQL Distilled");
            Book migratingMicroservice = service.book("Migrating to Microservice Databases");
            Book shack = service.book("The Shack");

            service.category(java, software);
            service.category(nosql, software);
            service.category(microService, software);

            service.category(effectiveJava, software);
            service.category(nosqlDistilled, software);
            service.category(migratingMicroservice, software);

            service.category(effectiveJava, java);
            service.category(nosqlDistilled, nosql);
            service.category(migratingMicroservice, microService);
            service.category(shack, romance);

            List<String> softwareCategories =service.softwareCategories();
            System.out.println("Software Categories = " + softwareCategories);

            List<String> softwareBooks = service.softwareBooks();
            System.out.println("Software Books = " + softwareBooks);

            List<String> softwareNoSQLBooks = service.softwareNoSQLBooks();
            System.out.println("Software and NoSQL Books = " + softwareNoSQLBooks);
        }
    }

    private AppBook() {
    }
}