How to reference a Composite Secondary Key - jpa

Question

The below examples show what I tried to reference an entity by a unique combination of columns that is not its primary key.
I want to do it that way because the referencing table contains all the necessary constituents of the referenced "Composite Secondary Key" but it does not contain the Primary Key.
How can I achieve this? (If possible without being Hibernate specific)
Base example
Suppose an entity has a primary key as well as a composite secondary key:
#Entity
#Table(name = "EXAMPLE_DATA",
uniqueConstraints = {
#UniqueConstraint(columnNames = {
"COMPOSITE_KEY_PART_1",
"COMPOSITE_KEY_PART_2"})
})
public class ExampleData {
#Id
#Column
private Long exampleDataId;
#Column(name = "COMPOSITE_KEY_PART_1")
private String compositeKeyPart1;
#Column(name = "COMPOSITE_KEY_PART_2")
private String compositeKeyPart2;
}
I would like to reference it from another table by its composite secondary key:
#Entity
#Table(name = "EXAMPLE")
public class Example {
#Id
#Column
private Long exampleId;
#Column(name = "COMPOSITE_KEY_PART_1")
private String compositeKeyPart1; // of ExampleData
#Column(name = "COMPOSITE_KEY_PART_2")
private String compositeKeyPart2; // of ExampleData
#MayToOne
#JoinColumn(name = "COMPOSITE_KEY_PART_1", insertable = false, updatable = false)
#JoinColumn(name = "COMPOSITE_KEY_PART_2", insertable = false, updatable = false)
private ExampleData exampleData;
}
However, this leads to
org.hibernate.AnnotationException:
A Foreign key refering com.example.ExampleData from com.example.Example has the wrong number of column. should be 1
Making a separate #Embeddable composite key
I tried making the secondary key embeddable
#Embeddable
public class CompositeKey implements Serializable {
#Column(name = "COMPOSITE_KEY_PART_1")
private String compositeKeyPart1;
#Column(name = "COMPOSITE_KEY_PART_2")
private String compositeKeyPart2;
}
and using it as an embedded object:
#Entity
#Table(name = "EXAMPLE_DATA",
uniqueConstraints = {
#UniqueConstraint(columnNames = {
"COMPOSITE_KEY_PART_1",
"COMPOSITE_KEY_PART_2"})
})
public class ExampleData {
#Id
#Column
private Long exampleDataId;
#Embedded
private CompositeKey compositeKey;
}
but that leads to the same exception:
org.hibernate.AnnotationException:
A Foreign key refering com.example.ExampleData from com.example.Example has the wrong number of column. should be 1
Using #EmbeddedId
Using #EmbeddedId instead of just #Embedded leads to issues with multiple keys
org.hibernate.AnnotationException:
com.example.CompositeKey must not have #Id properties when used as an #EmbeddedId: com.example.ExampleData.compositeKey
Having only a single key works but is undesirable
The only way I can actually make it work is by removing the primary key and making the composite key the primary key (but I don't want that)
#Entity
#Table(name = "EXAMPLE_DATA")
public class ExampleData {
// #Id // removing this primary key is undesirable
#Column
private Long exampleDataId;
#EmbeddedId // This now becomes the primary key
private CompositeKey compositeKey;
}