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Spring Data: Bridging Multiple Databases

Solution: Fine Calculation System

Explore how to implement a fine calculation system in Spring Data MongoDB by creating document classes, repositories, and methods for book loan, return, and fine calculation. Understand how to manage data with annotations, auditing, and repository queries to ensure accurate and efficient handling of book loans and fines.

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Solution

Let’s discuss the solution for implementing a fine calculation system.

Update the Book document

First, we add the Boolean available property to the Book class.

Java
package com.smartdiscover.document;
import lombok.Data;
import org.springframework.data.annotation.*;
import org.springframework.data.mongodb.core.mapping.DBRef;
import org.springframework.data.mongodb.core.mapping.Document;
import java.util.Date;
import java.util.List;
import java.util.stream.Collectors;
@Data
@Document
public class Book {
    @Id
    private String id;
    private String name;
    private String summary;
    private Boolean available;
    @CreatedBy
    private String createdBy;
    @CreatedDate
    private Date createdDate;
    @LastModifiedBy
    private String lastModifiedBy;
    @LastModifiedDate
    private Date lastModifiedDate;
    @DBRef
    private List<Author> authors;
    @Override
    public String toString() {
        return "Book{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", summary='" + summary + '\'' +
                ((null != authors) ? ", authors=" + authors.stream().map(i -> i.getFirstName()).collect(Collectors.toList()) + '\'' : "") +
                ", createdBy='" + createdBy + '\'' +
                ", createdDate='" + createdDate + '\'' +
                ", lastModifiedBy='" + lastModifiedBy + '\'' +
                ", lastModifiedDate='" + lastModifiedDate + '\'' +
                '}';
    }
}

Update the BookRepository

Then, we add the findByNameAndAvailableIsNullOrAvailableIsTrue method in the BookRepository interface to search for a book by matching the name and its availability as Null or True.

Java
package com.smartdiscover.repository;
import com.smartdiscover.document.Book;
import org.springframework.data.mongodb.repository.MongoRepository;
import java.util.List;
public interface BookRepository extends MongoRepository<Book, String> {
    Book findFirstByName(String name);
    List<Book> findAllByName(String name);
    Book findByNameAndAvailableIsNullOrAvailableIsTrue(String name);
    
}

Create the BookLoanEntry document

Then, we create the BookLoanEntry class in the com.smartdiscover.document package.

Java
package com.smartdiscover.document;
import lombok.Data;
import org.springframework.data.annotation.*;
import org.springframework.data.mongodb.core.mapping.DBRef;
import org.springframework.data.mongodb.core.mapping.Document;
import java.util.Date;
@Data
@Document
public class BookLoanEntry {
    @Id
    private String id;
    private String userFirstName;
    private String userLastName;
    @DBRef
    private Book book;
    private Date loanDate;
    private Date dueDate;
    private Date returnDate;
    private String status;
    @CreatedBy
    private String createdBy;
    @CreatedDate
    private Date createdDate;
    @LastModifiedBy
    private String lastModifiedBy;
    @LastModifiedDate
    private Date lastModifiedDate;
}

Explanation:

  • Lines 10–12: We add annotations like @Data and @Document to transform a class into a document.

  • Lines 18 and 19: We add the id identifier.

  • ...