休眠忽略左连接

Question

我有一个名为 SecurityContact 的表，它与另一个表 Contacts 具有多对一的关系。它有两个连接到联系人的列，其中一个称为 agentContact，另一个称为 auditContact。我正在尝试运行以下 HQL 查询：

SELECT sc FROM SecurityContact sc LEFT JOIN sc.agentContact ac LEFT JOIN sc.auditContact ac2 WHERE sc.securityId=:securityId2

然而，Hibernate 完全忽略了 LEFT JOIN 语句并继续生成利用内连接的 SQL。这根本不适合我的目的。我试过设置 fetch 注释，但没有运气。这个问题已经让我发疯了两天多，所以任何帮助都将不胜感激。

这是我的 SecurityContact 类的代码：

/**
 * The persistent class for the SecurityContact database table.
 * 
 */
@Entity
@FXClass(kind=FXClassKind.REMOTE)
public class SecurityContact implements Serializable {
    private static final long serialVersionUID = 1L;
    @Transient private String uid;
    @FXIgnore
    public String getUid() {
        if (uid == null) {
            uid = "" + securityContactId;
        }
        return uid;
    }

    public void setUid(String uid) {
        this.uid = uid;
    }

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    @Column(name="securityContact_id")
    private Long securityContactId;

    @Column(name="security_id")
    private String securityId;

    @Column(name="create_date")
    private String createDate;

    @Column(name="create_user")
    private String createUser;

    @Column(name="modify_date")
    private String modifyDate;

    @Column(name="modify_user")
    private String modifyUser;

    //uni-directional many-to-one association to AgentContact

    @ManyToOne
    @JoinColumn(name="agent_id", referencedColumnName="contact_id")
    private Contact agentContact;

    //uni-directional many-to-one association to AuditContact
    @ManyToOne
    @JoinColumn(name="audit_id", referencedColumnName="contact_id")
    private Contact auditContact;

    public SecurityContact() {
    }
    @FXKeyColumn
    public Long getSecurityContactId() {
        return this.securityContactId;
    }

    public void setSecurityContactId(Long securityContactId) {
        this.securityContactId = securityContactId;
    }

    public String getSecurityId() {
        return this.securityId;
    }

    public void setSecurityId(String securityId) {
        this.securityId = securityId;
    }

    public String getCreateDate() {
        return this.createDate;
    }

    public void setCreateDate(String createDate) {
        this.createDate = createDate;
    }

    public String getCreateUser() {
        return this.createUser;
    }

    public void setCreateUser(String createUser) {
        this.createUser = createUser;
    }

    public String getModifyDate() {
        return this.modifyDate;
    }

    public void setModifyDate(String modifyDate) {
        this.modifyDate = modifyDate;
    }

    public String getModifyUser() {
        return this.modifyUser;
    }

    public void setModifyUser(String modifyUser) {
        this.modifyUser = modifyUser;
    }
    @FXManyToOne(parent="parent", property="contactId")
    public Contact getAgentContact() {
        return this.agentContact;
    }

    public void setAgentContact(Contact agentContact) {
        this.agentContact = agentContact;
    }
    @FXManyToOne(parent="parent", property="contactId")
    public Contact getAuditContact() {
        return this.auditContact;
    }

    public void setAuditContact(Contact auditContact) {
        this.auditContact = auditContact;
    }

} 

这是从上述 HQL 生成的 SQL：

select securityco0_.agent_id as col_0_0_, securityco0_.audit_id as col_1_0_, securityco0_.create_date as col_2_0_, securityco0_.create_user as col_3_0_, securityco0_.modify_date as col_4_0_, securityco0_.modify_user as col_5_0_, securityco0_.securityContact_id as col_6_0_, securityco0_.security_id as col_7_0_, agentconta3_.contact_id as contact1_0_0_, agentconta4_.contact_id as contact1_0_1_, agentconta3_.bank_id as bank10_0_0_, agentconta3_.create_date as create2_0_0_, agentconta3_.create_user as create3_0_0_, agentconta3_.email as email0_0_, agentconta3_.fax as fax0_0_, agentconta3_.modify_date as modify6_0_0_, agentconta3_.modify_user as modify7_0_0_, agentconta3_.name as name0_0_, agentconta3_.phone as phone0_0_, agentconta4_.bank_id as bank10_0_1_, agentconta4_.create_date as create2_0_1_, agentconta4_.create_user as create3_0_1_, agentconta4_.email as email0_1_, agentconta4_.fax as fax0_1_, agentconta4_.modify_date as modify6_0_1_, agentconta4_.modify_user as modify7_0_1_, agentconta4_.name as name0_1_, agentconta4_.phone as phone0_1_ from SecurityContact securityco0_ left outer join AgentContact agentconta1_ on securityco0_.agent_id=agentconta1_.contact_id left outer join AgentContact agentconta2_ on securityco0_.audit_id=agentconta2_.contact_id inner join AgentContact agentconta3_ on securityco0_.agent_id=agentconta3_.contact_id inner join AgentContact agentconta4_ on securityco0_.audit_id=agentconta4_.contact_id where securityco0_.security_id=?

Answer 1

您的HQL join syntax 看起来很不稳定。试试这个：

SELECT sc
FROM SecurityContact sc
LEFT JOIN FETCH sc.agentContact
LEFT JOIN FETCH sc.auditContact
WHERE sc.securityId=:securityId2

Answer 2

我已经针对您的问题进行了一些测试，在我看来，您的映射可能有问题，或者您正在使用的 Hibernate（过时）版本中存在错误。

对于可选的@ManyToOne 关联，Hibernate 应该已经使用左连接来查询实体及其关联（因为它是查询根实体的唯一方法，无论是否关联实体为空）。

我在https://github.com/mattnworb/hibernate-sample 整理了一个示例项目来说明这一点。

在我的示例项目中，Employee 类具有 a unidirectional many-to-one mapping to the Team class：

/**
 * Unidirectional relationship between Employee and Team.
 */
@ManyToOne
@JoinColumn(name = "team_id")
private Team team;

在单元测试中，Employee.team 引用 is not-null when it is set in the DB 的测试和 DB 表中断言 Employee.team is null when not set 的另一个测试。

此外，Company 和 Employee 实体之间存在类似的双向关系，并进行了类似的测试。

最后，在日志中我可以看到，当 Hibernate 查询 Employee 实体时（使用简单的session.get(Employee.class, id)），它使用左连接来拉入teams 表（我自己添加了换行符）：

调试 org.hibernate.SQL - 选择employee0_.id 作为id1_2_，employee0_.company_id 作为company6_1_2_，employee0_.dateOfBirth 作为dateOfBi2_1_2_，employee0_.employmentStartDate 作为employme3_1_2_，employee0_.firstName 作为firstName1_2_，employee0_.lastName 作为lastName1_2_，employee0_.team_id作为 team7_1_2_，company1_.id 作为 id0_0_，company1_.name 作为 name0_0_，team2_.id 作为 id2_1_，team2_.name 作为 name2_1_
来自员工员工0_
在employee0_.company_id=company1_.id 上离开外部加入公司company1_
left external join teams team2_ on employee0_.team_id=team2_.id where employee0_.id=?

总而言之，为了让 Hibernate 在关联实体之间使用左连接，只要将关系设置为可选，就根本不需要特殊的 HQL 查询 - 一个简单的 session.get() 即可根实体应该使用左连接查询关联实体的表。如果您看到不同的结果，这表明您的 Hibernate 版本中存在错误（我在这里使用的是 3.6.6.Final），或者您的映射中有错误。