Hibernate and @JoinFormula: org.hibernate.mapping.Formula cannot be cast to org.hibernate.mapping.Column

I'm trying to write a hibernate adapter for an old database schema. This schema does not have a dedicated id column, but uses about three other columns to join data.

On some tables, I need to use coalesce. This is what I came up with so far:

About the definition:

• A car can have elements, assigned by the car's user or by the car's group of users.


• If FORIGN_ELEMENT holds a user's name, definition will be 'u'


• If FORIGN_ELEMENT holds a group's name, definition will be 'g'


• This also means, one table (CAR_TO_ELEMENT) is misused to map cars to elements and cargroups to elements. I defined a superclass CarElement and subclasses CarUserElement and CarGroupElement.


• state is either "active" or an uninteresting string


• I set definitition and state elsewhere, we do not need to worry about this.


• Use DEP_NR on the join table. If it's zero, use USR_DEP_NR. I did this with
  COALESCE(NULLIF())
  successfully in native SQL and want to achieve the same in Hibernate with Pojos.

@Entity

@Table(name="CAR")

public class Car extends TableEntry implements Serializable {

    @Id

    @Column(name="DEP_NR")

    private int depnr;



    @Id

    @Column(name="USER_NAME")

    @Type(type="TrimmedString")

    private String username;



    @ManyToOne(fetch = FetchType.EAGER, targetEntity=CarGroup.class)

    @JoinColumns(value={ 

            @JoinColumn(name="GROUP_NAME"),

            @JoinColumn(name="DEP_NR"),

            @JoinColumn(name="state"),

    })

    private CarGroup group;



    @OneToMany(fetch=FetchType.EAGER, targetEntity=CarUserElement.class, mappedBy="car")

    private Set<CarUserElement> elements;

}

@Entity

@Table(name="CAR_GROUP")

public class CarGroup extends TableEntry implements Serializable {

    @Id

    @Column(name="DEP_NR")

    private int depnr;



    @Id

    @Column(name="GROUP_NAME")

    @Type(type="TrimmedString")

    private String group;



    @ManyToOne(fetch = FetchType.EAGER, targetEntity=Car.class)

    @JoinColumns(value={ 

            @JoinColumn(name="GROUP_NAME"),

            @JoinColumn(name="DEP_NR"),

            @JoinColumn(name="state"),

    })

    private Set<Car> cars;



    @OneToMany(fetch=FetchType.EAGER, targetEntity=CarGroupElement.class, mappedBy="car")

    private Set<CarGroupElement> elements;

}

@MappedSuperclass

public class CarElement extends TableEntry {

    @Id

    @ManyToOne(fetch = FetchType.EAGER, targetEntity=Element.class)

    @JoinColumns(value={ 

            @JoinColumn(name="ELEMENT_NAME"),

            @JoinColumn(name="state"),

    })

    private Element element;

}

@Entity

@Table(name="CAR_TO_ELEMENT")

public class CarUserElement extends CarElement {

    @Id

    @Column(name="DEFINITION")

    private char definition;



    @Id

    @ManyToOne(fetch = FetchType.LAZY)

    @JoinColumnsOrFormulas(value = {

        @JoinColumnOrFormula(formula=@JoinFormula(value="COALESCE(NULLIF(DEP_NR, 0), USR_DEP_NR)", referencedColumnName="DEP_NR")),

        @JoinColumnOrFormula(column=@JoinColumn(name="FORIGN_ELEMENT", referencedColumnName="USER_NAME")),

        @JoinColumnOrFormula(column=@JoinColumn(name="STATE", referencedColumnName="STATE"))

    })

    private Car car;



}

@Entity

@Table(name="CAR_TO_ELEMENT")

public class CarGroupElement extends CarElement {

    @Id

    @Column(name="DEFINITION")

    private char definition;



    @Id

    @ManyToOne(fetch = FetchType.LAZY)

    @JoinColumnsOrFormulas(value = {

        @JoinColumnOrFormula(formula=@JoinFormula(value="COALESCE(NULLIF(DEP_NR, 0), USR_DEP_NR)", referencedColumnName="DEP_NR")),

        @JoinColumnOrFormula(column=@JoinColumn(name="FORIGN_ELEMENT", referencedColumnName="GROUP_NAME")),

        @JoinColumnOrFormula(column=@JoinColumn(name="STATE", referencedColumnName="STATE"))

    })

    private Car car;



}

Exception in thread "main" java.lang.ClassCastException: org.hibernate.mapping.Formula cannot be cast to org.hibernate.mapping.Column

    at org.hibernate.cfg.annotations.TableBinder.bindFk(TableBinder.java:351)

    at org.hibernate.cfg.annotations.CollectionBinder.bindCollectionSecondPass(CollectionBinder.java:1338)

    at org.hibernate.cfg.annotations.CollectionBinder.bindOneToManySecondPass(CollectionBinder.java:791)

    at org.hibernate.cfg.annotations.CollectionBinder.bindStarToManySecondPass(CollectionBinder.java:719)

    at org.hibernate.cfg.annotations.CollectionBinder$1.secondPass(CollectionBinder.java:668)

    at org.hibernate.cfg.CollectionSecondPass.doSecondPass(CollectionSecondPass.java:66)

    at org.hibernate.cfg.Configuration.originalSecondPassCompile(Configuration.java:1597)

    at org.hibernate.cfg.Configuration.secondPassCompile(Configuration.java:1355)

    at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1737)

    at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1788)