BookAvailability

  package bookrental.model.book;

import lombok.*;

import javax.persistence.*;
import javax.validation.constraints.NotNull;

@Getter
@Setter
@EqualsAndHashCode
@AllArgsConstructor
@NoArgsConstructor
public class BookMetaData {

    @NotNull
    BookMetadata book;
    boolean available;
}

BookMetaData

  package bookrental.model.book;

import lombok.*;

import javax.persistence.*;
import javax.validation.constraints.NotNull;

@Getter
@Setter
@EqualsAndHashCode
@AllArgsConstructor
@NoArgsConstructor
public class BookMetaData {

    @NotNull
    private String title;
    @NotNull
    private String author;
    @NotNull
    private String category;
}