Question

我有查询当我使用Group By语句运行时，我得到以下格式的结果。

Country     Region      Town
---------------------------------------
England     North       NewCastle
England     North       Manchester
England     North       Leeds
England     South       London
England     South       Bristol
England     South       Birmingham
England     South       Portsmouth
Norway      North       Trondheim
Norway      North       Tromso
Norway      South       Oslo
Norway      South       Stavanger
Norway      West        Bergen

结果返回一个JPA对象列表，如下所示

@Entity
@Indexed
@Table(name="Country")
public class Country extends AbstractDomainObject {

    private static final long serialVersionUID = 8619373591913330663L;

    private String country;
    private String region;
    private String town

    @Id 
    @Column(name="COUNTRY")
    public Long getCountry() {
        return batchNumber;
    }
    public void setCountry(String country) {
        this.country = country;
    }

    @Id
    @Column(name="REGION")
    public Date getRegion() {
        return region;
    }
    public void setRegion(String region) {
        this.region = region;
    }

    @Id
    @Column(name="TOWN")
    public String getTown() {
        return description;
    }
    public void setTown(String town) {
        this.description = description;
    }

    @Override
    public String toString() {
        return ToStringBuilder.reflectionToString(this);
    }
}

我必须循环遍历JPA对象列表并创建新对象。我似乎无法获得循环结构。我花了太多时间试图做到这一点，所以我想知道是否有一种更好，更简单的方法。我想要实现的是将数据存储在以下类型的集合中：

class CountryTowns{

    String Country;
    List<Region> regions;

    //getters and setters
}

class Region{
    String region;
    List<String> towns;

    //getters and setters;
}

要将数据存储在上面显示的对象中，我试图循环访问数据并创建对象，如果国家或城镇发生了变化，但我似乎无法做到正确。

List<CountryTowns> countryTowns = new ArrayList();
List<Country> countries = dataServicesFacade.getListOfCountries();
boolean firstIteration = false;

for(Country country : countries){

    if (firstIteration){
        CountryTowns countryTowns = new CountryTowns;
        Region region = new Region;
    }

    if(prevCountry.equals(country.getCountry())){
        if(prevRegion.equals(country.getRegion())){             

            region.setRegion(countryGetRegion())
            region.towns.add(country.getTown());            

        }else{          
            countryTowns.regions.add(region);
            Region region = new Region();
        }
    }else{
        CountryTowns countryTowns = new CountryTowns;
    }

    prevCountry = country.getCountry();
    prevRegion = country.getRegion();
}

对于列表比上面显示的列数多得多的列表，它可能会很快混淆。您如何解决上述问题，是否有推荐的方法或设计模式可以更容易地遍历列表？

遍历JPA对象列表并将其存储在非JPA对象中

0 个答案: