Question

奖励实体

@JsonIgnore
@ManyToMany(mappedBy="awards", fetch=FetchType.LAZY)
private Set<Winner> winners = new HashSet<>();

获胜者实体

@ManyToMany(fetch=FetchType.LAZY)
@JoinTable(name="AWARD_ASSIGNMENT", 
joinColumns={@JoinColumn(name="WINNER_ID", referencedColumnName="ID")}, 
inverseJoinColumns={@JoinColumn(name="AWARD_ID", referencedColumnName="ID")})
private Set<Award> awards = new HashSet<>();

我正在调用这个hibernate fetch方法

return getSession().createQuery("from Winner").list();

Hashcode等于奖励实体中的方法覆盖

@Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + (int) (id ^ (id >>> 32));
        result = prime * result + ((winners == null) ? 0 : winners.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Award other = (Award) obj;
        if (id != other.id)
            return false;
        if (winners == null) {
            if (other.winners != null)
                return false;
        } else if (!winners.equals(other.winners))
            return false;
        return true;
    }

获胜者实体

@Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((awards == null) ? 0 : awards.hashCode());
        result = prime * result + (int) (id ^ (id >>> 32));
        return result;
    }


    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Winner other = (Winner) obj;
        if (awards == null) {
            if (other.awards != null)
                return false;
        } else if (!awards.equals(other.awards))
            return false;
        if (id != other.id)
            return false;
        return true;
    }

覆盖equals和hashcode方法，因为多对多关系使用SET。

Answer 1

要记住的要点：

1）确保哈希码或相同方法中没有关联（一对多/多对多..等）。覆盖hashcode / equals方法时，使用使该对象唯一的字段（例如，FirstName + LastName +电话号码）尽量避免使用JPA生成的PK Id。

2）限制Jackson / Json序列化以避免深度遍历。

@JsonManagedReference
private Set<Award> awards = new HashSet<>();

@JsonBackReference
private Set<Winner> winners = new HashSet<>();

Hibernate ManyToMany映射无限的DB调用

1 个答案: