Hibernate OneToOne: Forced to chose between optional = false or cascade?

Question

In order to keep transfered data small I created two entities for my files in the database. The fileheader to keep some general information about the files and the fileblob, including fileId and the blob. Often, I only need to ask for general fileinformations.

So I need to load the fileblobs lazily.

As I learned in this discussion and that discussion. this could be achieved with optional = false. It works perfect to load the fileblobs lazily. Unfortunately it affects save by cascade.

So here is my attribute in the Fileh.class for the blob:

@OneToOne(mappedBy = "fileh", targetEntity = Fileblob.class, fetch = FetchType.LAZY, optional = false)
@org.hibernate.annotations.Cascade({ org.hibernate.annotations.CascadeType.SAVE_UPDATE, org.hibernate.annotations.CascadeType.LOCK })
private Fileblob fileblob;

If I now save a fileh with attached fileblob, this error is thrown:

org.hibernate.id.IdentifierGenerationException: null id generated for:class Fileblob

if i switch from id-generation strategy "identity" to "increment" this error is thrown:

ERROR SqlExceptionHelper:147 - Cannot add or update a child row: a foreign key constraint fails (`CORE`.`FILEBLOB`, CONSTRAINT

FKFILEBLOB412557 FOREIGN KEY (ID) REFERENCES FILEH (ID)) Query is: insert into CORE.FILEBLOB (FILEBLOB, ID) values (?, ?)

So there is a problem with generating the id... If i now turn off save by cascade my attribute looks like this.

@OneToOne(mappedBy = "fileh", targetEntity = Fileblob.class, fetch = FetchType.LAZY, optional = false)
private Fileblob fileblob;

In order to save now, I have to call

persistentSession.saveOrUpdate(fileh);
persistentSession.saveOrUpdate(fileblob);

Is this not just what CascadeType.SAVE_UPDATE is supposed to do? Why is this working for "manual cascading" but not automatically?

P.s.: To complete my example here the counterpart in fileblob.class

@PrimaryKeyJoinColumn   
@OneToOne(targetEntity=Fileh.class, fetch=FetchType.LAZY)   
@org.hibernate.annotations.Cascade({org.hibernate.annotations.CascadeType.SAVE_UPDATE, org.hibernate.annotations.CascadeType.LOCK}) 
@JoinColumns({ @JoinColumn(name="`ID`", referencedColumnName="`ID`", unique=true, nullable=false) })    
private Fileh fileh;

@Column(name="`ID`", nullable=false, insertable=false, updatable=false, unique=true)    
@Id 
@GeneratedValue(generator="FILEBLOB_FILEHID_GENERATOR") 
@org.hibernate.annotations.GenericGenerator(name="FILEBLOB_FILEHID_GENERATOR", strategy="foreign", parameters=@org.hibernate.annotations.Parameter(name="property", value="fileh")) 
private int filehId;

Answer 1

I encountered exactly the same issue and tried to solve it for several days! It turns out it's an issue which has lied in Hibernate's bug system for more than 2 years!

Though the answer here does help resolve the issue, we are forced to give up using Persist Cascade from the parent Entity (the inverse side, also the side with mappedBy defined)

Please see this link: https://hibernate.atlassian.net/browse/HHH-9670

If you want to apply lazy loading to a OneToOne relationship, and be able to do Persist cascade as usual, please leave a comment to show your concern for the issue!

Answer 2

Well first i would use JPA cascading instead of hibernate one:

@OneToOne(mappedBy = "fileh", fetch = FetchType.LAZY, optional = false)
private Fileblob fileblob;

And the Fileblob, well i think your configuration can be a bit simpler without those generators and stuff(assuming that the id should be actually a foreign key pointing to the Fileh.id).

@Column(name="`ID`", nullable=false, unique=true)    
@Id 
private int filehId;

@JoinColumn(name = "id", referencedColumnName = "id")
@OneToOne(cascade = {CascadeType.MERGE, CascadeType.PERSIST})
@MapsId
private Fileh fileh;