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Spring Data: Bridging Multiple Databases

Integration of POJO with the JDBC Repository

Explore integrating plain Java objects with Spring Data JDBC repositories to perform CRUD operations. Understand mapping strategies for many-to-many relationships and how to configure repositories for seamless data persistence and retrieval.

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Integrating a POJO class with a JDBC repository involves mapping the class fields to database columns and implementing CRUD operations. This enables seamless data persistence, retrieval, and manipulation by leveraging JDBC APIs to interact with the underlying database for efficient and reliable data storage.

POJOs

First, we create the Book and Author POJO classes referencing the book and author database tables. Let’s visualize a class diagram for our POJOs.

Book-Author class diagram
Book-Author class diagram

Here, we’ve taken a practical scenario where one book can have one or more authors, and one author can write one or more books. So, we have a many-to-many mapping between the Book and Author objects.

The Book POJO

First, let’s create the Book POJO class in the com.smartdiscover.entity package.

Java
package com.smartdiscover.entity;
import lombok.Data;
import org.springframework.data.annotation.*;
import org.springframework.data.relational.core.mapping.MappedCollection;
import org.springframework.data.relational.core.mapping.Table;
import java.util.Date;
import java.util.HashSet;
import java.util.Set;
@Data
@Table(name = "BOOK")
public class Book {
    @Id
    private long id;
    private String name;
    private String summary;
    @MappedCollection(idColumn = "BOOK_ID")
    private Set<AuthorBook> authors = new HashSet<>();
    @Override
    public String toString() {
        return "Book{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", summary='" + summary + '\'' +
                ", authors=" + authors.stream().mapToLong(i -> i.getAuthorId()).boxed().toList().toString() +
                '}';
    }
}

Explanation:

  • Line 12: We use Lombok’s @Data annotation to generate the getters and setters of the properties.
  • Line 13: We add the @Table annotation to connect the POJO with the BOOK table in the database.
  • Lines 16–20: We add properties like id,
...