@Entity
@Table(name = "product")
public class ProductEntity {
    @Id
    @Column(name = "id", nullable = false)
    private Long id = -1L;
    @Column(name = "name", nullable = false)
    private String name = "";
    @Column(name = "group_product_id", nullable = false)
    private Long groupProductId = -1L;

    // для JPA должен быть пустой конструктор
    public ProductEntity() {
    }

    public ProductEntity(Long id, String name, Long groupProductId) {
        this.id = id;
        this.name = name;
        this.groupProductId = groupProductId;
    }

    ...getters and setters...

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        ProductEntity productDB = (ProductEntity) o;
        return Objects.equals(id, productDB.id) && Objects.equals(name, productDB.name);
    }

    @Override
    public int hashCode() {
    return Objects.hash(id, name);
    }
}

@Entity
@Table(name = "group_product")
public class GroupProductEntity {
    @Id
    @Column(name = "id")
    private Long id = -1L;
    @Column(name = "name", nullable = false)
    private String name = "";
    @Column(name = "parent_id", nullable = false)
    private Long parentId = -1L;
    @Column(name = "is_last", nullable = false)
    private Boolean isLast = true;
    //TODO: можно добавить что-то типа tree index String "01.20.30..." или String "010230..."
    // для быстрой выборки групп без подзапросов

    public GroupProductEntity() {
    }

    public GroupProductEntity(Long id, String name, Boolean isLast, Long parentId) {
        this.id = id;
        this.name = name;
        this.parentId = parentId;
        this.isLast = isLast;
    }

    ...getters and setters...

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        ProductEntity productDB = (ProductEntity) o;
        return Objects.equals(id, productDB.id) && Objects.equals(name, productDB.name);
    }

    @Override
    public int hashCode() {
        return Objects.hash(id, name);
    }
}

@Repository
@Transactional
@Table(name = "product")
public interface ProductRepository extends JpaRepository<ProductEntity, Long> {
    List findAllByOrderByIdAsc();

    @Query(value = "SELECT max(id) FROM ProductEntity")
    Long getMaxId();

    List findByGroupProductIdOrderByIdAsc(Long groupId);

    @Query(value = "delete FROM ProductEntity")
//    @Sql("classpath:import_test.sql") // можно так
    @Modifying
    void reset();
}

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Modifying;
import org.springframework.data.jpa.repository.Query;
import org.springframework.stereotype.Repository;
import org.springframework.transaction.annotation.Transactional;
import ru.perm.v.easybot.entity.GroupProductEntity;

import java.util.List;

@Repository
@Transactional
public interface GroupProductRepository extends JpaRepository<GroupProductEntity, Long> {
    List findAllByOrderByIdAsc();

   /**
   * Get with SQL query
   */
    @Query(value = "SELECT max(id) FROM GroupProductEntity")
    Long getMaxId();

   /**
   * Select with JPA
   * select * from product where parent_id = :id order by id asc
   */
    List findByParentIdOrderByParentIdAsc(Long id);

   /**
   * Select with JPA
   */
    List findByParentIdOrderByParentIdAscIdAsc(Long id);

    /**
     * delete except ROOT with id=1 "IT products"
     * delete with query. @Modifying!!!
     */
    @Query(value = "delete FROM GroupProductEntity where ID>1")
    @Modifying
    void reset();
}

package ru.perm.v.parking.db;

import lombok.*;
import lombok.experimental.Accessors;
import lombok.experimental.FieldDefaults;

import javax.persistence.*;
import java.io.Serializable;
import java.util.HashSet;
import java.util.Set;

/**
 * Парковка. Содержит список машин, ктр. сейчас припаркованы.
 */
@Setter
@Getter
@NoArgsConstructor
@ToString
@EqualsAndHashCode
@Accessors(chain = true)
@FieldDefaults(level = AccessLevel.PRIVATE)
@Table(name = "parking")
@Entity
public class ParkingEntity implements Serializable {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    @Column(name = "address")
    private String address = "";
    @OneToMany(cascade = CascadeType.MERGE, fetch = FetchType.EAGER)
    @JoinTable(name = "parking_car",
            joinColumns = @JoinColumn(name = "parking_id"),
            inverseJoinColumns = @JoinColumn(name = "car_id"))
    Set cars = new HashSet<>();

}

package ru.perm.v.parking.db;

import lombok.*;
import lombok.experimental.FieldDefaults;

import javax.persistence.*;

/**
* Машина.
* Аттрибуты: госномер, марка
*/
@Setter
@Getter
@NoArgsConstructor
@ToString
@EqualsAndHashCode
@Entity
@FieldDefaults(level = AccessLevel.PRIVATE)
@Table(name = "car")
public class CarEntity {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    @Column(name = "gos_number")
    private String gosNumber = "";
    @Column(name = "model")
    private String model = "";
}