@AnyMetaDef(
    name = "myMetaDef",
    metaType = "string",
    idType = "long",
    metaValues = {
        @MetaValue(targetEntity = Book.class, value = "BOOK"),
        @MetaValue(targetEntity = Movie.class, value = "MOVIE")
    }
)

@Entity
public class User {
    @Id
    private Long id;

    @ManyToAny
    @AnyMetaDef(
        name = "itemMetaDef",
        metaType = "string",
        idType = "long",
        metaValues = {
            @MetaValue(targetEntity = Book.class, value = "BOOK"),
            @MetaValue(targetEntity = Movie.class, value = "MOVIE")
        }
    )
    @JoinTable(
        name = "user_items",
        joinColumns = @JoinColumn(name = "user_id"),
        inverseJoinColumns = @JoinColumn(name = "item_id")
    )
    @Column(name = "item_type") // Дискриминатор
    private List<Object> items; // Может содержать Book и Movie
}

@Entity
public class Review {
    @Id
    private Long id;

    @Any(metaDef = "contentMetaDef", metaColumn = @Column(name = "content_type"))
    @JoinColumn(name = "content_id")
    private Object content; // Может быть Book или Movie
}

@AnyMetaDef(
    name = "mediaMetaDef",
    metaType = "string",  // Тип столбца-дискриминатора (varchar)
    idType = "long",      // Тип ID целевой сущности
    metaValues = {
        @MetaValue(targetEntity = Book.class, value = "BOOK"),
        @MetaValue(targetEntity = Movie.class, value = "MOVIE")
    }
)

@Entity
public class Library {
    @Id
    private Long id;

    @ManyToAny
    @AnyMetaDef(
        name = "mediaMetaDef",
        metaType = "string",
        idType = "long",
        metaValues = {
            @MetaValue(targetEntity = Book.class, value = "BOOK"),
            @MetaValue(targetEntity = Movie.class, value = "MOVIE")
        }
    )
    @JoinTable(
        name = "library_items",
        joinColumns = @JoinColumn(name = "library_id"),
        inverseJoinColumns = @JoinColumn(name = "item_id")
    )
    @Column(name = "item_type") // Столбец для дискриминатора
    private List<Object> items; // Может содержать Book и Movie
}

@Entity
public class Review {
    @Id
    private Long id;

    @Any(metaDef = "mediaMetaDef")
    @JoinColumn(name = "content_id")
    @Column(name = "content_type") // Дискриминатор
    private Object content; // Book или Movie
}

import java.util.HashMap;
import java.util.Map;

class Employee160425 {
    String name;
    
    Employee160425(String name) { this.name = name; }
    
    @Override
    public boolean equals(Object o) {
        return this.name.equals(((Employee160425)o).name);
    }
    
    @Override
    public int hashCode() {
        return name.length();
    }
}

public class Task160425 {
    public static void main(String[] args) {
        Map<Employee160425, String> map = new HashMap<>();
        Employee160425 e1 = new Employee160425("John");
        Employee160425 e2 = new Employee160425("Jane");
        
        map.put(e1, "Developer");
        map.put(e2, "Manager");
        
        e1.name = "Johnny";
        
        System.out.println(map.get(e1));
        System.out.println(map.get(new Employee160425("John")));
    }
}

@Entity
public class User {
    @Id
    private Long id;

    @NaturalId(mutable = false) // Неизменяемый (оптимизирует кеширование)
    private String email;

    @NaturalId(mutable = true)  // Изменяемый (редкий случай)
    private String passportNumber;
}

@Entity
@Table(uniqueConstraints = @UniqueConstraint(columnNames = "isbn"))
public class Book {
    @Id
    private Long id;

    @NaturalId // immutable=false по умолчанию
    private String isbn;
}

Book book = session.bySimpleNaturalId(Book.class)
    .load("978-3-16-148410-0");

@Entity
public class Order {
    @ManyToOne
    @NotFound(action = NotFoundAction.IGNORE) // Игнорировать отсутствие пользователя
    private User user;
}

-- order.user_id = 999, но users.id = 999 не существует
@NotFound(action = IGNORE) → order.user = null.

@EventListener(ApplicationReadyEvent.class)
public void checkBrokenReferences() {
    // Ручная проверка...
}

logging.level.org.hibernate=DEBUG

@Entity
public class Comment {
    @ManyToOne
    @NotFound(action = NotFoundAction.IGNORE)
    private Post post; // Если post удалён, comment.post = null
}

public CommentDTO getComment(Long id) {
    Comment comment = commentRepository.findById(id).orElseThrow();
    if (comment.getPost() == null) {
        log.warn("Пост для комментария {} не найден", id);
    }
    return toDto(comment);
}

import java.util.HashMap;

class Key170425 {
    int id;
    
    Key170425(int id) {
        this.id = id;
    }
    
    @Override
    public int hashCode() {
        return id % 2;
    }

    @Override
    public boolean equals(Object o) {
        return this.id % 2 == ((Key170425)o).id % 2;
    }
}

public class Task170425 {
    public static void main(String[] args) {
        HashMap<Key170425, String> map = new HashMap<>();
        map.put(new Key170425(1), "Apple");
        map.put(new Key170425(2), "Banana");
        map.put(new Key170425(3), "Cherry");
        
        System.out.println(map.size());
    }
}

@Entity  
public class Order {  
    @ManyToOne  
    @OnDelete(action = OnDeleteAction.CASCADE) // При удалении User удалятся его Order  
    private User user;  
}  

@Entity  
public class Comment {  
    @ManyToOne  
    @OnDelete(action = OnDeleteAction.CASCADE) // Удалить комментарии при удалении Post  
    private Post post;  
}  

@Entity  
public class Employee {  
    @ManyToOne  
    @OnDelete(action = OnDeleteAction.SET_NULL) // department_id = NULL при удалении Department  
    private Department department;  
}