And I meant to add that you could also consider the two tables to be
in an inheritance relationship in which the table with the "logical
foreign key" maps to an Entity that is a subclass of the other Entity.
Craig
On Jul 16, 2010, at 10:39 PM, Craig L Russell wrote:
There's no common definition for "shared primary key" that I'm aware
of.
But let's just go and create a definition that might make sense and
see how JPA would deal with it.
If two tables have the same type of primary key, and some values of
one table's PK are also values of another table's PK, this might be
a definition of shared primary key.
You can further constrain the problem by requiring that all values
of one table's PK must be values of another table's PK, in effect
defining a logical foreign key, whether or not the logical foreign
key is actually declared as a foreign key.
If there is no logical foreign key, then I'd agree that JPA doesn't
address it. A relationship has to have an "owning" side and without
any constraints, there cannot be an owner.
If there is a logical foreign key, then there are concepts that
apply to modeling the tables' relationship.
If you want to model the two tables as a single Entity, then you can
use secondary tables. This model assumes that for each row in the
secondary table there is a corresponding row in the primary table.
Fields in the Entity can be mapped to columns in the secondary table.
If you want to model the two tables as two Entities, then you can
declare a one-to-one relationship between them. You can then
navigate between instances of the two Entities, and have the fields
of each Entity map to columns in each Entity's own primary table.
Craig
On Jul 16, 2010, at 6:57 PM, KARR, DAVID (ATTSI) wrote:
Would you say that the following statement is accurate or not?
"The JPA specification doesn't have a way to deal with a shared
primary
key."
Isn't this what "secondary-table" addresses? Are there other
strategies
that apply to this?
Craig L Russell
Architect, Oracle
http://db.apache.org/jdo
408 276-5638 mailto:[email protected]
P.S. A good JDO? O, Gasp!
Craig L Russell
Architect, Oracle
http://db.apache.org/jdo
408 276-5638 mailto:[email protected]
P.S. A good JDO? O, Gasp!
