source: src/main/java/com/project/beautycenter/model/Uslugi.java

package com.project.beautycenter.model;

import org.hibernate.annotations.OnDelete;
import org.hibernate.annotations.OnDeleteAction;

import javax.persistence.*;
import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;

import static java.lang.Float.NaN;

@Entity
@Table(name = "uslugi",schema = "project")
public class Uslugi {
    @Id
    @Column(name = "usluga_id", nullable = false, length = 100)
    private String id;

    @Column(name = "dejnost", length = 100)
    private String dejnost;

    @Column(name = "cena", nullable = false, length = 100)
    private String cena;

    @OneToMany(mappedBy = "uslugi",cascade = CascadeType.ALL, orphanRemoval = true, fetch = FetchType.LAZY)
    private Set<Ocena> ocenas = new LinkedHashSet<>();

    public Uslugi(){}
    public Uslugi(String id, String dejnost, String cena) {
        this.id = id;
        this.dejnost = dejnost;
        this.cena = cena;
    }

    public Set<Ocena> getOcenas() {
        return ocenas;
    }

    public void setOcenas(Set<Ocena> ocenas) {
        this.ocenas = ocenas;
    }

    public Float getAvgRating(){
        List<Ocena> oceni = oceniToList();
        float sum = 0;
        float num = 0;
        for (Ocena x : oceni){
            if(x.getUslugi().id.equals(this.id)){
                sum+= x.getVrednost();
                num++;
            }

        }
        float avg = sum/num;
            return avg;
    }
    public List<Ocena> oceniToList(){
        List<Ocena> oceni = new ArrayList<Ocena>(ocenas.size());
        for (Ocena x : ocenas)
            oceni.add(x);
        return oceni;
    }
    @PreRemove
    private void removeUslugaOdOcena() {
        for (Ocena o : oceniToList()) {
            o.getUslugi().oceniToList().remove(this);
        }
    }
    public List<Ocena> removeOcenaOdUsluga(Ocena o){
        oceniToList().remove(o);
        return oceniToList();
    }

    public String getCena() {
        return cena;
    }

    public void setCena(String cena) {
        this.cena = cena;
    }

    public String getDejnost() {
        return dejnost;
    }

    public void setDejnost(String dejnost) {
        this.dejnost = dejnost;
    }

    public String getId() {
        return id;
    }

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