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这是我的数据库的快速图表。

http://img17.imageshack.us/img17/2474/mpd.png

在这个方案中，我创建了 JPA 实体（对于所有带有红色方块的表）。

我想创建一个 JPQL 查询来获取所有具有引用的飞机，引用由参数给出的引用类型定义。

我试过了 ： SELECT DISTINCT a FROM Aircraft a JOIN FETCH a.references r WHERE EXISTS (SELECT ref FROM Reference ref WHERE ref = r AND ref.referenceType.id = :id)

但是我有一个错误，因为 Eclipse 不喜欢别名，JOIN FETCH a.references *r*并且请求在 JUnit 测试中不起作用。

这里我的实体没有 getter/setter ：

飞机

@Entity
@Table(name = "T_R_AIRCRAFT_AIR", uniqueConstraints = @UniqueConstraint(columnNames = "AIR_NAME"))
public class Aircraft implements java.io.Serializable {

    @Id
    @Column(name = "AIR_ID", unique = true, nullable = false)
    @TableGenerator(name="aircraftSeqStore", 
        table="T_S_APP_SEQ_STORE_AST", 
        pkColumnName="AST_SEQ_NAME",
        valueColumnName = "AST_SEQ_VALUE",
        pkColumnValue = "T_R_AIRCRAFT_AIR.AIR_ID", 
        allocationSize=1)
    @GeneratedValue(strategy=GenerationType.TABLE, 
        generator="aircraftSeqStore")       
    private Integer id;

    @Column(name = "AIR_NAME", unique = true, nullable = false, length = 50)
    private String name;

    @ManyToMany(fetch = FetchType.LAZY)
    @JoinTable(name = "T_J_REF_AIR_RFA", 
               joinColumns = { @JoinColumn(name = "RFA_AIR_ID", nullable = false, updatable = false) }, 
               inverseJoinColumns = { @JoinColumn(name = "RFA_REF_ID", nullable = false, updatable = false) })
    private Set<Reference> references = new HashSet<Reference>(0);

    @ManyToMany(fetch = FetchType.LAZY)
    @JoinTable(name = "T_J_MAN_AIR_MNA", 
               joinColumns = { @JoinColumn(name = "MNA_AIR_ID", nullable = false, updatable = false) }, 
               inverseJoinColumns = { @JoinColumn(name = "MNA_MAN_ID", nullable = false, updatable = false) })  
    private Set<Manual> manuals = new HashSet<Manual>(0);

    @OneToMany(fetch = FetchType.LAZY, 
               mappedBy = "aircraft",
               cascade = { CascadeType.REMOVE })
    private Set<UserConfig> userConfigs = new HashSet<UserConfig>(0);
}

** 参考 **

@Entity
@Table(name = "T_E_REFERENCE_REF", 
       uniqueConstraints = @UniqueConstraint(columnNames = "REF_IDENTIFIER"))
public class Reference implements java.io.Serializable {

    @Id
    @Column(name = "REF_ID", unique = true, nullable = false)
    @TableGenerator(name="referenceSeqStore", 
        table="T_S_APP_SEQ_STORE_AST", 
        pkColumnName="AST_SEQ_NAME",
        valueColumnName = "AST_SEQ_VALUE",
        pkColumnValue = "T_E_REFERENCE_REF.REF_ID", 
        allocationSize=1)
    @GeneratedValue(strategy=GenerationType.TABLE, generator="referenceSeqStore")                   
    private Integer id;

    @Column(name = "REF_IDENTIFIER", unique = true, nullable = false, length = 50)  
    private String identifier;

    @Column(name = "REF_LINK")  
    private String link;

    @Column(name = "REF_OBSERVATIONS", length = 4000)
    private String observations;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "REF_RFT_ID", nullable = false)  
    private ReferenceType referenceType;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "REF_MAN_ID")    
    private Manual manual;  

    @OneToMany(fetch = FetchType.LAZY, 
               mappedBy = "reference",
               cascade = { CascadeType.REMOVE })
    private Set<Translation> translations = new HashSet<Translation>(0);

    @ManyToMany(fetch = FetchType.LAZY)
    @JoinTable(name = "T_J_REF_AIR_RFA", 
               joinColumns = { @JoinColumn(name = "RFA_REF_ID", nullable = false, updatable = false) },
               inverseJoinColumns = { @JoinColumn(name = "RFA_AIR_ID", nullable = false, updatable = false) })
    private Set<Aircraft> aircrafts = new HashSet<Aircraft>(0);
}

** 参考类型 **

@Entity
@Table(name = "T_R_REFERENCE_TYPE_RFT", 
       uniqueConstraints = @UniqueConstraint(columnNames = "RFT_TYPE"))
public class ReferenceType implements java.io.Serializable {

    @Id
    @Column(name = "RFT_ID", unique = true, nullable = false)
    @TableGenerator(name="referenceTypeSeqStore", 
        table="T_S_APP_SEQ_STORE_AST", 
        pkColumnName="AST_SEQ_NAME",
        valueColumnName = "AST_SEQ_VALUE",
        pkColumnValue = "T_R_REFERENCE_TYPE_RFT.RFT_ID", 
        allocationSize=1)
    @GeneratedValue(strategy=GenerationType.TABLE, generator="referenceTypeSeqStore")                   
    private Integer id;

    @Column(name = "RFT_TYPE", unique = true, nullable = false, length = 50)    
    private String type;

    @OneToMany(fetch = FetchType.LAZY, 
               mappedBy = "referenceType", 
               cascade = { CascadeType.REMOVE })    
    private Set<Reference> references = new HashSet<Reference>(0);

    @OneToMany(fetch = FetchType.LAZY, 
               mappedBy = "referenceType",
               cascade = { CascadeType.REMOVE })    
    private Set<UserConfig> userConfigs = new HashSet<UserConfig>(0);
}

PS：我忘了说飞机和参考之间添加了一个表格。这是手动表。但我不认为有影响。

PS2：JPA 实现是由 Hibernate 完成的。

知道如何进行多重连接吗？谢谢 ！

4

1 回答 1

7

您可以更轻松地执行查询，如下所示：

SELECT DISTINCT a FROM Aircraft a JOIN FETCH a.references r 
LEFT JOIN FETCH a.manuals 
WHERE r.referenceType.id = :id

我已经添加了join fetch a.manuals，否则我得到了LazyInitializationException. 添加LEFT以防止缺少手册影响输出。

于 2012-08-15T10:29:15.870 回答