JpaSystemException: Error accessing field [XXXXXX] by reflection for persistent property [XXXXXX] : 1

Question

I'm fairly new to JPA/Hibernate, so I decided to create a Library Rest Application to improve. I'm attempting to save a libraryCatalogItem with a libraryId FK so I know which Library a libraryCatalogItem belongs to.

Below is the outline for my LibraryCatalogItem.class:

import com.LibraryApplication.Library.model.Library;
import lombok.Getter;
import lombok.Setter;
import org.springframework.beans.factory.annotation.Autowired;

import javax.persistence.*;

//Created class abstract so this class can't be implemented
@Entity
//Implemented Single Table strategy for Hibernate Inheritance Mapping and used Discriminator values to identify different records
@DiscriminatorColumn(name = "library_catalog_item_type", discriminatorType = DiscriminatorType.STRING)
public abstract class LibraryCatalogItem {

    @Id
    @Column(name = "catalog_item_primary_key")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    protected Integer Id;


    //declared private for encapsulation
    @Getter
    @Setter
    protected String title, genre;

    @JoinColumn(name = "library_fk"/*, nullable = false*/) //TODO uncomment nullable = false, once I figure out how to have foreign key
    @ManyToOne(targetEntity = Library.class, cascade=CascadeType.ALL)
    protected Integer libraryFk;

    protected LibraryCatalogItem() {
    }

    @Override
    public String toString() {
        return "LibraryCatalogItem{" +
                "title='" + title + '\'' +
                ", genre='" + genre + '\'' +
                ", id=" + Id +
                '}';
    }

}

and this is my Library class:

import com.LibraryApplication.Library.model.LibraryCatalogItems.LibraryCatalogItem;
import lombok.Getter;
import lombok.Setter;

import javax.persistence.*;
import java.util.List;

@Entity
public class Library {

    @Id
    @Column(name="library_primary_key")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Getter
    @Setter
    protected Integer libraryPrimaryKey;

    @Getter
    @Setter
    private Integer phoneNumber;

    @Getter
    @Setter
    private String name, address, email;

    //TODO make libraryId foreign key relate to LibraryCatalogItem Table
    @OneToMany(mappedBy = "libraryFk", targetEntity = LibraryCatalogItem.class, fetch = FetchType.LAZY)
    private List<LibraryCatalogItem> libraryCatalogItems;

}

The issue I am facing is when I send a request to save a libraryCatalogItem I receive the following issue:

org.springframework.orm.jpa.JpaSystemException: Error accessing field [protected java.lang.Integer com.LibraryApplication.Library.model.Library.libraryPrimaryKey] by reflection for persistent property [com.LibraryApplication.Library.model.Library#libraryPrimaryKey] : 1; nested exception is org.hibernate.property.access.spi.PropertyAccessException: Error accessing field [protected java.lang.Integer com.LibraryApplication.Library.model.Library.libraryPrimaryKey] by reflection for persistent property [com.LibraryApplication.Library.model.Library#libraryPrimaryKey] : 1] with root cause

java.lang.IllegalArgumentException: Can not set java.lang.Integer field com.LibraryApplication.Library.model.Library.libraryPrimaryKey to java.lang.Integer
    at java.base/jdk.internal.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(UnsafeFieldAccessorImpl.java:167) ~[na:na]
    at java.base/jdk.internal.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(UnsafeFieldAccessorImpl.java:171) ~[na:na]
    at java.base/jdk.internal.reflect.UnsafeFieldAccessorImpl.ensureObj(UnsafeFieldAccessorImpl.java:58) ~[na:na]
    at java.base/jdk.internal.reflect.UnsafeObjectFieldAccessorImpl.get(UnsafeObjectFieldAccessorImpl.java:36) ~[na:na]

Would anyone be able to point me in the right direction in resolving this issue? Thank you.

Answer 1

The libraryPrimaryKey property is missing a @Getter and @Setter. I think without a getter and setter, JPA won't be able to access the property. Here is some info about it: https://docs.oracle.com/cd/E19798-01/821-1841/bnbqb/index.html

"Persistent instance variables must be declared private, protected, or package-private and can be accessed directly only by the entity class's methods. Clients must access the entity's state through accessor or business methods."

Answer 2

This isn't an exact fix to the issue above, but what I ended up doing is taking a different approach to essentially reach the same solution. The intended goal was to ensure that each child entity had a relation to a library entity by including libraryFk column in child entity table. So instead of using SingleTableInheritance Mapping I used MappedSuperClassInheritance Mapping.

Please refer to below article: https://www.baeldung.com/hibernate-inheritance