How to retrieve data from a many-to-many relationship in hibernate?

Question

I have four tables as shown in the below diagram.

The relationship between restaurant and category is many-to-many. For that a new table named restaurant_category is being used. I set the relationship between Restaurant and Categories as below.

RestaurantEntity.java

================

package com.upgrad.FoodOrderingApp.service.entity;

import javax.persistence.*;
import javax.validation.constraints.Size;
import java.io.Serializable;
import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.List;
import java.util.UUID;

@Entity
@Table(name = "restaurant")

@NamedQueries(
        {       @NamedQuery(name = "getAllRestaurants", query = "select res from RestaurantEntity res")
        }
)

public class RestaurantEntity implements Serializable {

    @Id
    @Column(name = "id")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;

    @Column(name = "UUID")
    @Size(max = 200)
    private UUID uuid;

    @Column(name = "restaurant_name")
    @Size(max = 50)
    private String restaurantName;

    @Column(name = "photo_url")
    @Size(max = 225)
    private String photoURL;

    @Column(name = "customer_rating")
    private BigDecimal customeRating;

    @Column(name = "average_price_for_two")
    private Integer avgPriceForTwo;

    public List<CategoryEntity> getCategories() {
        return categories;
    }

    public void setCategories(List<CategoryEntity> categories) {
        this.categories = categories;
    }

    @Column(name = "number_of_customers_rated")
    private Integer numbrOfCustomersRated;

    @ManyToOne(fetch = FetchType.EAGER)
    @JoinColumn(name = "address_id")
    private AddressEntity addressEntity;

    @ManyToMany(cascade=CascadeType.ALL)
    @JoinTable(name="restaurant_category", joinColumns={@JoinColumn(referencedColumnName="ID")}
            , inverseJoinColumns={@JoinColumn(referencedColumnName="ID")})
    private List<CategoryEntity> categories = new ArrayList<>();

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public UUID getUuid() {
        return uuid;
    }

    public void setUuid(UUID uuid) {
        this.uuid = uuid;
    }

    public String getRestaurantName() {
        return restaurantName;
    }

    public void setRestaurantName(String restaurantName) {
        this.restaurantName = restaurantName;
    }

    public String getPhotoURL() {
        return photoURL;
    }

    public void setPhotoURL(String photoURL) {
        this.photoURL = photoURL;
    }

    public BigDecimal getCustomeRating() {
        return customeRating;
    }

    public void setCustomeRating(BigDecimal customeRating) {
        this.customeRating = customeRating;
    }

    public Integer getAvgPriceForTwo() {
        return avgPriceForTwo;
    }

    public void setAvgPriceForTwo(Integer avgPriceForTwo) {
        this.avgPriceForTwo = avgPriceForTwo;
    }

    public Integer getNumbrOfCustomersRated() {
        return numbrOfCustomersRated;
    }

    public void setNumbrOfCustomersRated(Integer numbrOfCustomersRated) {
        this.numbrOfCustomersRated = numbrOfCustomersRated;
    }

    public AddressEntity getAddressEntity() {
        return addressEntity;
    }

    public void setAddressEntity(AddressEntity addressEntity) {
        this.addressEntity = addressEntity;
    }
}

CategoryEntity.java

===============

package com.upgrad.FoodOrderingApp.service.entity;

import org.apache.commons.lang3.builder.EqualsBuilder;
import org.apache.commons.lang3.builder.HashCodeBuilder;
import org.apache.commons.lang3.builder.ToStringBuilder;
import org.apache.commons.lang3.builder.ToStringStyle;

import javax.persistence.*;
import javax.validation.constraints.Size;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
import java.util.UUID;

@Entity
@Table(name = "category")
public class CategoryEntity implements Serializable {

    @Id
    @Column(name = "ID")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    public Integer id;

    @Column(name = "UUID")
    @Size(max = 200)
    public UUID uuid;

    public List<RestaurantEntity> getRestaurants() {
        return restaurants;
    }

    public void setRestaurants(List<RestaurantEntity> restaurants) {
        this.restaurants = restaurants;
    }

    @Column(name = "CATEGORY_NAME")
    @Size(max = 255)

    public String category_name;

    @ManyToMany(mappedBy="categories")
    private List<RestaurantEntity> restaurants = new ArrayList<>();

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public UUID getUuid() {
        return uuid;
    }

    public void setUuid(UUID uuid) {
        this.uuid = uuid;
    }

    public String getCategory_name() {
        return category_name;
    }

    public void setCategory_name(String category_name) {
        this.category_name = category_name;
    }

    @Override
    public boolean equals(Object obj) {
        return new EqualsBuilder().append(this, obj).isEquals();
    }

    @Override
    public int hashCode() {
        return new HashCodeBuilder().append(this).hashCode();
    }

    @Override
    public String toString() {
        return ToStringBuilder.reflectionToString(this, ToStringStyle.MULTI_LINE_STYLE);
    }
}

Also I used a namedQuery in RestaurantEntity as below,

@NamedQueries(
        {       @NamedQuery(name = "getAllRestaurants", query = "select res from RestaurantEntity res")
        }
)

This namedQuery returns all the data required for Restaurants,and its related object -address. But it does not return data for its related categories. Am I doing something wrong in setting up the relationship between Restaurants and Categories?. Please guide me.

So what my expectation is that named query should return data for related categories as well.

Note : In terminal I am getting below error,

org.postgresql.util.PSQLException: ERROR: column categories0_.categories_id does not exist

Please post the entire entity source. – Alexpandiyan Chokkan Jun 14 '19 at 08:53 — Alexpandiyan Chokkan, Jun 14 '19 at 08:53
Please check , edited my question to include it. – user3656231 Jun 14 '19 at 09:00 — user3656231, Jun 14 '19 at 09:00

score 0 · Answer 1 · answered Jun 14 '19 at 09:16

0

You have to correct the mapping by adding the join columns names:

@ManyToMany(cascade=CascadeType.ALL)
@JoinTable(name="restaurant_category", joinColumns={@JoinColumn(name = "RESTAURANT_ID", referencedColumnName="ID")}
                , inverseJoinColumns={@JoinColumn(name = "CATEGORY_ID", referencedColumnName="ID")})
private List<CategoryEntity> categories = new ArrayList<>();

answered Jun 14 '19 at 09:16

hasnae

2,137
17
21

I tried this but getting : java.lang.StackOverflowError: null – user3656231 Jun 14 '19 at 09:23
What hibernate version do you use? – hasnae Jun 14 '19 at 09:36

score 0 · Answer 2 · answered Jun 14 '19 at 09:17

0

Please change your JoinTable column names as below.

@ManyToMany(cascade=CascadeType.ALL)
    @JoinTable(name="restaurant_category", joinColumns={@JoinColumn(name="restaurant_id")}
            , inverseJoinColumns={@JoinColumn(name="category_id")})
    private List<CategoryEntity> categories = new ArrayList<>();

answered Jun 14 '19 at 09:17

Alexpandiyan Chokkan

1,025
1
10
30

I tried this but getting : java.lang.StackOverflowError: null – user3656231 Jun 14 '19 at 09:23
You have to use @JsonBackReference to solve the stackoverflow memory error. Please refer this answer https://stackoverflow.com/a/37394318/7458887 – Alexpandiyan Chokkan Jun 14 '19 at 09:34

How to retrieve data from a many-to-many relationship in hibernate?

2 Answers2