Question

我在hibernate实例中有一个名为keywords的实体。它存储单词列表和每个单词出现的次数。言语不是唯一的。我想总结列表中每个单词的总和。我使用HQL

query select keyword, sum(keywordcount) from Keywords as Keywords group by keyword order by sum(keywordcount) desc

这给了我正确的结果。我遇到的问题是，当我提交此查询时，我得到一个java.lang.Object对象列表。有没有办法告诉HQL给我一个类型为关键字的对象列表，因为它们具有我想要的结构。

@Entity
@Table(name = "keywords", catalog = "akiradev")
public class Keywords implements java.io.Serializable {

// Fields

private Integer id;
private Documents documents;
private String keyword;
private Integer keywordcount;

// Constructors

/** default constructor */
public Keywords() {
}

/** full constructor */
public Keywords(Documents documents, String keyword, Integer keywordcount) {
    this.documents = documents;
    this.keyword = keyword;
    this.keywordcount = keywordcount;
}

// Property accessors
@Id
@GeneratedValue(strategy = IDENTITY)
@Column(name = "id", unique = true, nullable = false)
public Integer getId() {
    return this.id;
}

public void setId(Integer id) {
    this.id = id;
}

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "document_id")
public Documents getDocuments() {
    return this.documents;
}

public void setDocuments(Documents documents) {
    this.documents = documents;
}

@Column(name = "keyword")
public String getKeyword() {
    return this.keyword;
}

public void setKeyword(String keyword) {
    this.keyword = keyword;
}

@Column(name = "keywordcount")
public Integer getKeywordcount() {
    return this.keywordcount;
}

public void setKeywordcount(Integer keywordcount) {
    this.keywordcount = keywordcount;
}
}

-------查询--------

public List<Keywords> getKeywordSum() {
    try {

        String queryString = "select keyword, sum(keywordcount) from Keywords as Keywords group by keyword order by sum(keywordcount) desc";
        Query queryObject = getSession().createQuery(queryString);
        List<Keywords> results = (List<Keywords>) queryObject.list();
        return results;
    } catch (RuntimeException re) {
        log.error("finding Documents in descending time order failed", re);
        throw re;
    }
}

Answer 1

在此处使用Keyword作为返回类型没有多大意义，因为查询结果与关键字的身份不同。但是，您可以创建DTO来表示此查询的结果

public class KeywordStats {
    private String keyword;
    private int count;
    public KeywordStats(String keyword, int count) { ... }
    ...
}

并使用构造函数语法从查询中返回它：

select new KeywordStats(keyword, sum(keywordcount)) from Keywords as Keywords group by keyword order by sum(keywordcount) desc

实际上，您可以使用相同的方法返回Keyword，但我不推荐它，因为它是滥用实体对象。

我可以为HQL查询指定结果对象类型吗？

1 个答案: