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为什么在Hibernate/JPA实体中避免使用Lombok @EqualsAndHashCode?

Lombok 是一个非常受欢迎和有用的图书馆。尽管如此，请注意Lombok @EqualsAndHashCode对实体的影响可能会带来严重问题。

实体应实施equals()和hashCode()。主要问题是Hibernate要求实体在其所有状态转换（瞬态，附加，分离和删除）中等于自身。使用Lombok @EqualsAndHashCode不会尊重此要求。

避免下面这些方法 ：

1. 避免使用的Lombok默认行为@EqualsAndHashCode：

@Entity
@EqualsAndHashCode
<b>public</b> <b>class</b> LombokDefaultProduct implements Serializable {

    <b>private</b> <b>static</b> <b>final</b> <b>long</b> serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    <b>private</b> Long id;

    <b>private</b> String name;
    <b>private</b> String code;

2. 避免使用只有主键的Lombok@EqualsAndHashCode

@Entity
@EqualsAndHashCode(exclude = {<font>"name"</font><font>, </font><font>"code"</font><font>})
<b>public</b> <b>class</b> LombokIdProduct implements Serializable {

    <b>private</b> <b>static</b> <b>final</b> <b>long</b> serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    <b>private</b> Long id;

    <b>private</b> String name;
    <b>private</b> String code;
</font>

3. 避免使用默认equals()和hashCode()，下面实体没有编写自己的这两个方法，使用的是默认，不推荐这样做：

@Entity
<b>public</b> <b>class</b> DefaultProduct implements Serializable {

    <b>private</b> <b>static</b> <b>final</b> <b>long</b> serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    <b>private</b> Long id;

    <b>private</b> String name;
    <b>private</b> String code;

    <b>public</b> Long getId() {
        <b>return</b> id;
    }

    <b>public</b> <b>void</b> setId(Long id) {
        <b>this</b>.id = id;
    }

    <b>public</b> String getName() {
        <b>return</b> name;
    }

    <b>public</b> <b>void</b> setName(String name) {
        <b>this</b>.name = name;
    }

    <b>public</b> String getCode() {
        <b>return</b> code;
    }

    <b>public</b> <b>void</b> setCode(String code) {
        <b>this</b>.code = code;
    }

}

4. 避免使用只依赖主键的equals()和hashCode()：

@Entity
<b>public</b> <b>class</b> IdProduct implements Serializable {

    <b>private</b> <b>static</b> <b>final</b> <b>long</b> serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    <b>private</b> Long id;

    <b>private</b> String name;
    <b>private</b> String code;

    <b>public</b> Long getId() {
        <b>return</b> id;
    }

    <b>public</b> <b>void</b> setId(Long id) {
        <b>this</b>.id = id;
    }

    <b>public</b> String getName() {
        <b>return</b> name;
    }

    <b>public</b> <b>void</b> setName(String name) {
        <b>this</b>.name = name;
    }

    <b>public</b> String getCode() {
        <b>return</b> code;
    }

    <b>public</b> <b>void</b> setCode(String code) {
        <b>this</b>.code = code;
    }

    @Override
    <b>public</b> <b>int</b> hashCode() {
        <b>int</b> hash = 3;
        hash = 89 * hash + Objects.hashCode(<b>this</b>.id);
        <b>return</b> hash;
    }

    @Override
    <b>public</b> <b>boolean</b> equals(Object obj) {
        <b>if</b> (<b>this</b> == obj) {
            <b>return</b> <b>true</b>;
        }
        <b>if</b> (obj == <b>null</b>) {
            <b>return</b> false;
        }
        <b>if</b> (getClass() != obj.getClass()) {
            <b>return</b> false;
        }
        <b>final</b> IdProduct other = (IdProduct) obj;
        <b>if</b> (!Objects.equals(<b>this</b>.id, other.id)) {
            <b>return</b> false;
        }
        <b>return</b> <b>true</b>;
    }
    
}

推荐这些方法： 1. 依靠@NaturalId