问题
I use Hibernate to access to a legacy DB. For some tables the parent-child reference integrity is not enforced, and the long 0 value is used instead of NULL for some "parent" columns in child tables to denote "no parent".
I still want to use these relations in @ManyToOne and @OneToMany fields, but get EntityNotFound error since the 0 value does not correspond to any record in master table.
What are my options?
回答1:
Use the NotFound annotation:
@NotFound(action = NotFoundAction.IGNORE)
See http://docs.jboss.org/hibernate/core/3.6/reference/en-US/html_single/#mapping-declaration-manytoone
回答2:
You can map it to java.lang.Long which default value is null. Or you can use a @PostLoad and null it if 0. You can also use a @Formula and ignore 0.
The @Formula as written in their documentation can be used to join conditions.
Since I don't know your data model providing a valid example is tricky. Try with:
id_fk is not null or id_fk <> 0
block.
If it does not suit your needs you can write you own Query loader
If you are using some sort of logging enable the show_sql property. And add to your config the org.hibernate.sql DEBUG.
回答3:
Instead of the @JoinColumn could be used @JoinFormula. Like this
@JoinFormula(value="CASE the0isNullColumn WHEN 0 THEN NULL ELSE the0isNullColumn END")
The expression means we check the column and if it's 0 return NULL. Then hibernate doesn't search for the related entity.
来源：https://stackoverflow.com/questions/8038737/hibernate-handle-long-0-value-instead-of-null-in-manytoone-relations