When implementing composite primary keys in Hibernate or other ORMs there are up to three places where to put the insertable = false, updatable = false in composite primary key constellations that use identifying relationships (FKs that are part of the PK):
- Into the composite PK class' @Column annotation (@Embeddable classes only) or
- Into the entity class' association @JoinColumn/s annotation or
- Into the entity class' redundant PK property's @Column annotation (@IdClass classes only)
The third is the only way to do with @IdClass and JPA 1.0 AFAIK. See http://en.wikibooks.org/wiki/Java_Persistence/Identity_and_Sequencing#Primary_Keys_through_OneToOne_Relationships. I will consider only cases 1. and 2.
Q:
Which way is the preferred place to put the "insertable = false, updatable = false" to generally?
I have experienced problems with Hibernate concerning this question. For example, Hibernate 3.5.x will complain about the Zips table
CREATE TABLE Zips
(
country_code CHAR(2),
code VARCHAR(10),
PRIMARY KEY (country_code, code),
FOREIGN KEY (country_code) REFERENCES Countries (iso_code)
)
with:
org.hibernate.MappingException: Repeated column in mapping for entity: com.kawoolutions.bbstats.model.Zip column: country_code (should be mapped with insert="false" update="false")
org.hibernate.mapping.PersistentClass.checkColumnDuplication(PersistentClass.java:676)
org.hibernate.mapping.PersistentClass.checkPropertyColumnDuplication(PersistentClass.java:698)
...
As you can see the country_code column is both PK and FK. Here are its classes:
Entity class:
@Entity
@Table(name = "Zips")
public class Zip implements Serializable
{
@EmbeddedId
private ZipId id;
@ManyToOne
@JoinColumn(name = "country_code", referencedColumnName = "iso_code")
private Country country = null;
...
}
Composite PK class:
@Embeddable
public class ZipId implements Serializable
{
@Column(name = "country_code", insertable = false, updatable = false)
private String countryCode;
@Column(name = "code")
private String code;
...
}
When putting the insertable = false, updatable = false into the entity class association's @JoinColumn all exceptions disappear and everything work fine. However, I don't see why the above code should not be working. It might be Hibernate having problems with this. Is the described a Hibernate bug, as it doesn't seem to evaluate @Column "insertable = false, updatable = false"?
In essence, what's the standard JPA way, the best practice, or preference where to put "insertable = false, updatable = false"?
Best Answer
Let me answer step by step.
1. When do you need ` insertable = false, updatable = false`?
Let's look at the below mapping,
Here we are referring to the same column in the table using two different properties. In the below code,
What will Hibernate do here??
To prevent these kind of inconsistency, Hibernate is asking you to specify the update point of relationships. Which means you can refer to the same column in the table
n
number of times but only one of them can be used to update and all others will be read only.2. Why is Hibernate complaining about your mapping?
In your
Zip
class you are referring to the Embedded id classZipId
that again contains the country code. As in the above scenario now you have a possibility of updating thecountry_code
column from two places. Hence the error given by Hibernate is proper.3. How to fix it in your case?
No. Ideally you want your
ZipId
class to generate the id, so you should not addinsertable = false, updatable = false
to the countryCode inside theZipId
. So the fix is as below modify thecountry
mapping in yourZip
class as below,Hope this helps your understanding.