Multi-Column Join in Hibernate JPA Annotations

Question

I have two entities which I would like to join through multiple columns  These columns are shared by an  Embeddable object that is shared by both entities  In the example below  Foo can have only one Bar but Bar can have multiple Foos  where AnEmbeddableObject is a unique key for Bar   Here is an example    Entity  Table name    foo   public class Foo        Id      Column name    id        GeneratedValue generator    seqGen        SequenceGenerator name    seqGen   sequenceName    FOO ID SEQ   allocationSize   1      private Long id       Embedded     private AnEmbeddableObject anEmbeddableObject       ManyToOne targetEntity   Bar class  fetch   FetchType LAZY       JoinColumns             JoinColumn name    column 1   referencedColumnName    column 1             JoinColumn name    column 2   referencedColumnName    column 2             JoinColumn name    column 3   referencedColumnName    column 3             JoinColumn name    column 4   referencedColumnName    column 4              private Bar bar              rest of class     And the Bar class    Entity  Table name    bar   public class Bar        Id      Column name    id        GeneratedValue generator    seqGen        SequenceGenerator name    seqGen   sequenceName    BAR ID SEQ   allocationSize   1      private Long id       Embedded     private AnEmbeddableObject anEmbeddableObject              rest of class     Finally the AnEmbeddedObject class    Embeddable public class AnEmbeddedObject        Column name    column 1       private Long column1       Column name    column 2       private Long column2       Column name    column 3       private Long column3       Column name    column 4       private Long column4              rest of class     Obviously the schema is poorly normalised  it is a restriction that AnEmbeddedObject s fields are repeated in each table   The problem I have is that I receive this error when I try to start up Hibernate   org hibernate AnnotationException  referencedColumnNames column 1  column 2  column 3  column 4  of Foo bar referencing Bar not mapped to a single property   I have tried marking the JoinColumns are not insertable and updatable  but with no luck  Is there a way to express this with Hibernate JPA annotations

User · Answer

If this doesn t work I m out of ideas  This way you get the 4 columns in both tables  as Bar owns them and Foo uses them to reference Bar  and the generated IDs in both entities  The set of 4 columns has to be unique in Bar so the many-to-one relation doesn t become a many-to-many    Embeddable public class AnEmbeddedObject        Column name    column 1       private Long column1       Column name    column 2       private Long column2       Column name    column 3       private Long column3       Column name    column 4       private Long column4      Entity public class Foo        Id      Column name    id        GeneratedValue generator    seqGen        SequenceGenerator name    seqGen   sequenceName    FOO ID SEQ   allocationSize   1      private Long id       ManyToOne fetch   FetchType LAZY       JoinColumns            JoinColumn name    column 1   referencedColumnName    column 1             JoinColumn name    column 2   referencedColumnName    column 2             JoinColumn name    column 3   referencedColumnName    column 3             JoinColumn name    column 4   referencedColumnName    column 4              private Bar bar      Entity  Table uniqueConstraints    UniqueConstraint columnNames          column 1        column 2        column 3        column 4      public class Bar        Id      Column name    id        GeneratedValue generator    seqGen        SequenceGenerator name    seqGen   sequenceName    BAR ID SEQ   allocationSize   1      private Long id       Embedded     private AnEmbeddedObject anEmbeddedObject

User · Answer

Hibernate is not going to make it easy for you to do what you are trying to do  From the Hibernate documentation       Note that when using referencedColumnName to a non primary key column  the associated class has to be Serializable  Also note that the referencedColumnName to a non primary key column has to be mapped to a property having a single column  other cases might not work    emphasis added    So if you are unwilling to make AnEmbeddableObject the Identifier for Bar then Hibernate is not going to lazily  automatically retrieve Bar for you   You can  of course  still use HQL to write queries that join on AnEmbeddableObject  but you lose automatic fetching and life cycle maintenance if you insist on using  a multi-column non-primary key for Bar

User · Answer

This worked for me   In my case 2 tables foo and boo have to be joined based on 3 different columns Please note in my case  in boo the 3 common columns are not primary key  i e   one to one mapping based on 3 different columns   Entity  Table name    foo   public class foo implements Serializable        Column name  foocol1       private String foocol1        add getter setter      Column name  foocol2       private String foocol2        add getter setter      Column name  foocol3       private String foocol3        add getter setter     private Boo boo      private int id       Id      GeneratedValue strategy   GenerationType IDENTITY       Column name    brsitem id   updatable   false      public int getId                 return this id            public void setId int id                this id   id             OneToOne      JoinColumns                 JoinColumn updatable false insertable false  name  foocol1   referencedColumnName  boocol1             JoinColumn updatable false insertable false  name  foocol2   referencedColumnName  boocol2             JoinColumn updatable false insertable false  name  foocol3   referencedColumnName  boocol3                   public Boo getBoo                 return boo            public void setBoo Boo boo                this boo   boo                Entity  Table name    boo   public class Boo implements Serializable       private int id       Column name  boocol1       private String boocol1        add getter setter      Column name  boocol2       private String boocol2        add getter setter      Column name  boocol3       private String boocol3        add getter setter      Id      GeneratedValue strategy   GenerationType IDENTITY       Column name    item id   updatable   false      public int getId                 return id            public void setId int id                this id   id

[java] Multi-Column Join in Hibernate/JPA Annotations

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