[FIXED] I can't create many to many relation in spring boot hibernate

Issue

I am trying to create a relation between category and product classes. I thought many to many relationship would be the best fit. However when I run the application I got org.hibernate.MappingException: property-ref [_com_eCommerce_ecommerce_model_Product_listOfCategories] not found on entity [com.eCommerce.ecommerce.model.Product] error. What could be the problem ?

Here is my Product class.

package com.eCommerce.ecommerce.model;

import lombok.Getter;
import lombok.NoArgsConstructor;
import lombok.Setter;
import javax.persistence.*;
import java.util.HashSet;
import java.util.Set;


@NoArgsConstructor
@Entity
@Getter
@Setter
@Table(name="Product")
public class Product {
    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE)
    private int productId;
    private int stockNumber;
    @ManyToMany
    @JoinTable(name = "products_categories",
    joinColumns = {
            @JoinColumn(name = "product",referencedColumnName = "productId",nullable = false,updatable = false)
    },
    inverseJoinColumns = {
            @JoinColumn(name = "category",referencedColumnName = "categoryName",nullable = false,updatable = false)
    })
     Set<Category> listOfCategories = new HashSet<>();
}

Category Class

package com.eCommerce.ecommerce.model;


import lombok.Data;
import lombok.NoArgsConstructor;

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

@Data
@NoArgsConstructor
@Entity
@Table(name = "Category")
public class Category {

    private int categoryParentNumber;
    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE)
    private int categoryId;
    private String categoryName;
    @ManyToMany(mappedBy = "listOfCategories",fetch = FetchType.LAZY)
    private Set<Product> listOfProducts = new HashSet<>();
    
}

Solution

The problem is the column naming.

Column name is not productId it is product_id, and to be able to use referencedColumnName you have to use @Column(name = "product_id") naming.

Also referenced column must be @Id and categoryName is not @Id.

Working example:

@Entity
public class Product {

  @Id
  @GeneratedValue(strategy = GenerationType.SEQUENCE)
  @Column(name = "product_id", nullable = false)
  private int productId;

  private int stockNumber;

  @ManyToMany(cascade = { CascadeType.ALL })
  @JoinTable(
        name = "products_categories_j",
        joinColumns = {
                @JoinColumn(name = "product_id", referencedColumnName = "product_id", nullable = false,updatable = false)
        },
        inverseJoinColumns = { @JoinColumn(name = "category_id", referencedColumnName = "category_id", nullable = false, updatable = false) }
  )
  private Set<Category> listOfCategories = new HashSet<>();
}


@Entity
public class Category {

  private int categoryParentNumber;

  @Id
  @GeneratedValue(strategy = GenerationType.SEQUENCE)
  @Column(name = "category_id", nullable = false)
  private int categoryId;

  @Column(name = "category_name", nullable = false)
  private String categoryName;

  @ManyToMany(mappedBy = "listOfCategories", fetch = FetchType.LAZY)
  private Set<Product> listOfProducts = new HashSet<>();

}

Answered By - Gergo
Answer Checked By - Katrina (JavaFixing Volunteer)