关于 redis的 set 去重疑问

谁践踏了优雅 2022-04-13 12:26 354阅读 0赞

set 本质是hashmap，去重也就是hashmap的去重，hashcode 和equals方法。

那么问题来了，当存储到redis 中的时候 redis是怎么实现去重的呢

用不包含父类的方式来设置区别

@Entity
    @Table(name = "CarBrand")
    @Data
    //@EqualsAndHashCode(callSuper=true)
    @AllArgsConstructor
    @NoArgsConstructor
    public class CarBrand extends BaseAdminWithoutIdEntity implements Comparable<CarBrand> {
    
        private static final long serialVersionUID = -8981328316599991382L;
        @Column(columnDefinition = "varchar(20)  COMMENT '车厂商名'")
        private String name;
        @Column(columnDefinition = "TINYINT(1) DEFAULT '0' COMMENT '是否热门'")
        private Boolean isHot;
    
        @Column(columnDefinition = "INT(4) DEFAULT '9999' COMMENT '排序'")
        private Integer sort;
    
        @Column(columnDefinition = "char(1)  COMMENT '首字母'")
        private String letter;
    
        @Column(columnDefinition = "varchar(250)  COMMENT '图片地址'")
        private String url;
    
        public CarBrand(String name, String url, String id) {
            this.name = name;
            this.url = url;
            super.setId(id);
        }
    
        @Override
        public int compareTo(CarBrand o) {
            int i = this.getSort() - o.getSort();
            return i;
        }
    }

CarBrand carBrand1 = new CarBrand();
    carBrand1.setName("zym");
    carBrand1.setId("13213");
    CarBrand carBrand2 = new CarBrand();
    carBrand2.setName("zym");
    redisTemplate.opsForSet().add("zym",carBrand1);
    redisTemplate.opsForSet().add("zym",carBrand2);
    System.out.println(redisTemplate.opsForSet().members("zym"));

控制台打印

[CarBrand(name=zym, isHot=null, sort=null, letter=null, url=null)]

也就是说，members返回的东西是已经去重了的，跟set集合内容一样，但是在redis 中却显示了两条数据，如下图

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM1OTg3NTY3_size_16_color_FFFFFF_t_70][]

这就说明了数据是在取出来之后去重的了，追看 members方法源码，该方法给出了答案

static <T extends Collection<?>> T deserializeValues(@Nullable Collection<byte[]> rawValues, Class<T> type,
    			@Nullable RedisSerializer<?> redisSerializer) {
    		// connection in pipeline/multi mode
    		if (rawValues == null) {
    			return (T) CollectionFactory.createCollection(type, 0);
    		}
    
    		Collection<Object> values = (List.class.isAssignableFrom(type) ? new ArrayList<>(rawValues.size())
    				: new LinkedHashSet<>(rawValues.size()));
    		for (byte[] bs : rawValues) {
    			values.add(redisSerializer.deserialize(bs));
    		}
    
    		return (T) values;
    	}

我是不是很无聊。。。

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM1OTg3NTY3_size_16_color_FFFFFF_t_70]: /images/20220413/151fa04ab25a4f44bedfc5907f2775c3.png