JPA / Hibernate加入恒定价值

我正在尝试使用join语句中的常量值连接到同一个表中的不同实体。 在SQL中，我会做这样的事情……

SELECT * FROM owner o JOIN types t on t.owner_id = o.id AND t.type = 'A' -- ^^^^^^^^^^^^^^^^ THIS IS WHAT I AM TRYING TO REPLICATE 

在Java + JPA / Hibernate中，我试图做这样的事情……

 @Entity @Table(name = "OWNER") public class Owner { @Id @Column(name="ID") private Long id @OneToOne(mappedBy = "owner", fetch = FetchType.EAGER, cascade = CascadeType.ALL) @JoinColumns({ @JoinColumn(name = "ID", referencedColumnName = "ID"), @JoinColumn(constantValue = "A", referencedColumnName="type")}) // ^^^^^^^^^^^^^^^^^^^ I AM LOOKING FOR SOMETHING THAT DOES THIS. // constantValue IS NOT A VALID ARGUMENT HERE. private TypeA inspectionSnapshot; @OneToOne(mappedBy = "owner", fetch = FetchType.EAGER, cascade = CascadeType.ALL) @JoinColumns({ @JoinColumn(name = "ID", referencedColumnName = "ID"), @JoinColumn(constantValue = "B", referencedColumnName="type")}) private TypeB inspectionSnapshot; /* Getters & Setters ... */ } @Entity @Table(name = "TYPES") @Inheritance(strategy = InheritanceType.SINGLE_TABLE) @DiscriminatorColumn(name = "TYPE", discriminatorType = DiscriminatorType.STRING) public abstract class BaseType { @Id @OneToOne @JoinColumn(name = "OWNER_ID", referencedColumnName="ID") private Owner id; @Id @Column(name = "TYPE") private char type /* Getters & Setters ... */ } @Entity @DiscriminatorValue("A") public class TypeA extends BaseType { /* All functionality in BaseType */ } @Entity @DiscriminatorValue("B") public class TypeA extends BaseType { /* All functionality in BaseType */ } 

提前致谢！

Answer 1

你正在寻找非标准的连接。 这是处理这种情况的文档：

http://docs.oracle.com/cd/E13189_01/kodo/docs40/full/html/ref_guide_mapping_notes_nonstdjoins.html

希望能帮助到你！

Answer 2

如果您不介意使用特定于Hibernate的注释，可以尝试使用@WhereJoinTable注释，例如：

 @OneToOne(mappedBy = "owner", fetch = FetchType.EAGER, cascade = CascadeType.ALL) @JoinColumn(name = "ID", referencedColumnName = "ID") @WhereJoinTable(clause = "TYPE = 'A'") private TypeA inspectionSnapshot; 

请注意， clause属性必须包含SQL，而不是JPQL，因此您需要使用数据库列名而不是JPA实体字段名。

Answer 3

尝试将常量指定为公式的值

 @JoinColumnsOrFormulas({ @JoinColumnOrFormula(formula=@JoinFormula(value="'A'", referencedColumnName="type")), @JoinColumnOrFormula(column = @JoinColumn("id", referencedColumnName="id")) }) private TypeA inspectionSnapshot;