对象A

@Entity
@Table(name = "td_spider_cfg")
public class SpiderCfg implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String netName;
    private String columnUrl;
    private String netUrl;
    private String columnName;
    private String columnPattern;
    private String columnPagePattern;
    private int depth = 1;
    private int isPage ;
    private int isUpdateSpider;
    private int isRepeat;
    private String cron;
    private int threadNum = 3;
    private String spiderType;

    @OneToMany(fetch=FetchType.EAGER,cascade=CascadeType.ALL)
    @JoinColumn(name="cfgId")
    private Set<SpiderCfgPattern> targetPatterns;
}

@Entity
@Table(name = "td_spider_cfg_pattern")
public class SpiderCfgPattern implements Serializable{

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String url;
    private String pattern;
    private Long cfgId;
}

我在更新对象A的时候，调用的是jpa的save方法。更新操作成功。但是关联的td_spider_cfg_pattern表里面之前的数据，并没有被删除，而是被update了。查看sql。如下：

，数据库里面出现了垃圾数据。（我的本意是想把之前在）td_spider_cfg_pattern表里面的关联数据删掉，再保存，但是jpa是update set=null ,然后保存。

请问我要怎么写代码，才能是正确的。

目前保存的代码如下：

@ResponseBody
    @RequestMapping(value = "/save", method = RequestMethod.POST)
    public String save(SpiderCfg spiderCfg, String urls) throws Exception {
        String columnPattern = UrlPattern.build(spiderCfg.getColumnUrl()).getPathPattern().toString();
        spiderCfg.setColumnPattern(columnPattern);
        String[] turls = urls.split("\n");
        Set<SpiderCfgPattern> set = Sets.newHashSet();
        for (String url : turls) {
            if (StringUtils.isNotBlank(url)) {
                SpiderCfgPattern p = new SpiderCfgPattern();
                p.setUrl(url);
                p.setPattern(UrlPattern.build(url).getPathPattern().toString());
                set.add(p);
            }
        }
        spiderCfg.setTargetPatterns(set);
        SpiderCfg res = spiderService.saveSpiderCfg(spiderCfg);
        return "true";
    }

求各位帮我看看。