Question

在使用hibernate和jpa的spring mvc应用程序中，WordKey实体和Concept实体之间存在多对多的关系。 WordKey有concepts个集合，Concept有wordkeys个集合。我不想使用fetchType=EAGER，因为性能是一个问题。相反，一旦用户选择了WordKey，我希望使用Collection<Concept> selectedKeyWord作为参数的查询结果填充wk并返回与基础数据库中的concepts关联的WordKey集合。如何在JPQL中编写此查询？

这是我到目前为止的查询。它不起作用（见下面的错误）：

@SuppressWarnings("unchecked")
public Collection<Concept> findConceptsForKeyWord(ConcWordKey wk) {
    Query query = this.em.createQuery(
        "SELECT DISTINCT concept FROM Concept concept join concept.wordkeys k WHERE k.name =:wk"
    );
    query.setParameter("wk", wk.getName());
    Collection<Concept> result = (Collection<Concept>) query.getResultList();
    return result;
}

以下是上述代码生成的hibernate查询。请注意，它正在寻找一个虚构的concept_wordkey表，而不是使用下面wordkey_junction实体代码中指定的WordKey连接表：

select distinct conc0_.effectiveTime as effectiv1_52_,
 conc0_.id as id2_52_,
 from concept conc0_
 inner join concept_wordkey wordkeys1_
 on conc0_.effectiveTime=wordkeys1_.concept_effectiveTime
 and conc0_.id=wordkeys1_.concept_id
 inner join wordkey conc2_
 on wordkeys1_.wordkeys_keyword=conc2_.keyword
 where conc2_.keyword=?

堆栈跟踪中生成的特定错误是：

com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException:  
Table 'mydb.concept_wordkey' doesn't exist

以下是Concept实体：

@Entity
@Table(name = "concept")
public class Concept implements Serializable{

    @EmbeddedId
    public EmbedPK conceptPk;

    @ManyToMany(cascade={CascadeType.ALL})
    private Set<WordKey> wordkeys;

    public EmbedPK getConceptPk(){return conceptPk;}

    protected Set<WordKey> getWordkeysInternal() {
        if (this.wordkeys == null) {this.wordkeys = new HashSet<WordKey>();}
        return this.wordkeys;
    }

    public List<WordKey> getWordkeys() {
        List<WordKey> sortedWordkeys = new ArrayList<WordKey>(getWordkeysInternal());
        PropertyComparator.sort(sortedWordkeys, new MutableSortDefinition("wordkey", true, true));
        return Collections.unmodifiableList(sortedWordkeys);
    }

    public WordKey getWordkey(String s) {return getWordkey(s, false);}

    public WordKey getWordkey(String ps, boolean ignoreNew) {
        ps = ps.toLowerCase();
        for (WordKey s1 : getWordkeysInternal()) {
            if (!ignoreNew || !s1.isNew()) {
                String keyword = s1.getName();
                keyword = keyword.toLowerCase();
                if (keyword.equals(ps)) {return s1;}
            }
        }
        return null;
    }
}

以下是WordKey实体：

@Entity
@Table(name = "wordkey")
public class WordKey {

    @Id
    @Column(name="keyword")
    private String name;

    @ManyToMany(cascade = {CascadeType.ALL})
    @JoinTable(name="wordkey_junction",
        joinColumns={@JoinColumn(name="keyword")},
        inverseJoinColumns={@JoinColumn(name="conceptid"),@JoinColumn(name="effectiveTime")})
    private Set<Concept> concepts = new HashSet<Concept>();

    public String getName(){return name;}
    public void setName(String nm){name=nm;}

    protected Set<Concept> getConceptsInternal() {
        if (this.concepts == null) {this.concepts = new HashSet<Concept>();}
        return this.concepts;
    }

    public List<Concept> getConcepts() {
        List<Concept> sortedConcepts = new ArrayList<Concept>(getConceptsInternal());
        PropertyComparator.sort(sortedConcepts, new MutableSortDefinition("conceptid", true, true));
        return Collections.unmodifiableList(sortedConcepts);
    }

    public Concept getConcept(BigInteger s) {return getConcept(s, false);}

    public Concept getConcept(BigInteger ps, boolean ignoreNew) {
        for (Concept s1 : getConceptsInternal()) {
            if (!ignoreNew || !s1.isNew()) {
                BigInteger compName = s1.getConceptPk().getId();
                if (compName == ps) {return s1;}
            }
        }
        return null;
    }
}

Answer 1

我认为您的@ManyToMany(cascade={CascadeType.ALL})课程中的Concept需要一个mappedBy。添加将注释更改为@ManyToMany(cascade={CascadeType.ALL}, mappedBy="concepts")并再次尝试。

你需要这个来告诉Hibernate将你的多对多wordKey集合映射到Concept类的WordKey集合，这将依次将您的wordkey_junction表暴露给集合。

如果这不起作用或您不想要双向关系，请告诉我。

Answer 2

您需要指定mid（外部参照）表。

@ManyToMany(cascade = {CascadeType.ALL})
    @JoinTable(name = "midTableName",
            joinColumns = {@JoinColumn(name = "foreignKey")},
            inverseJoinColumns = {@JoinColumn(name = "OtherEntityForeignKey")})

注意 - 这是具有规范化的ManyToMany Mapping的一般方式。如果你能用表结构更新问题，你可以得到一个好的答案。

hibernate在多对多关系的查询中找不到联结表

2 个答案: