Questions on Single Table Inheritance
Questions on Single Table Inheritance
- Subject: Questions on Single Table Inheritance
- From: Owen McKerrow <email@hidden>
- Date: Thu, 31 Mar 2005 14:18:40 +1000
Hi All,
Switching around one of my apps so that it use single table
inheritance. I've read up on it in Apple's "Using EOModler" and Chuck's
book, but I still have a couple of questions.
So I have a Member table ( will be parent ) and Im going to create to
Sub Tables, called Researcher and Student.
I thought that once I had created these sub-entities that I delete the
attributes from them that I don't want. e.g. we don't need the students
room number but we do need it for researcher, so I remove the phone
number from the Student entity. However EOModler then starts to
complain when I save it that the Sub-Table is missing one of the
parents attributes. can I just ignore this complaint ? Am I doing it
the right way ?
Also Im trying to figure out if I will need to have instances of member
( i.e. the parent class will be concrete ). I will never just make a
"Member" they will always be either a Student or a Researcher BUT I
will need a combine array of the two of them, where I won't care which
type Im dealing with i.e. displaying the authors of a book, written by
both researcher and students.
And if I have to keep Member concrete does this mean I need to give it
a restricting qualifier ? i.e. its own value for the Type column ?
And finally there is a table called Member_Details which has 2 BLOB's
in it ( its in its own table for efficiencies sake ), but only
researchers need an instance of this table. So Im assuming under Member
I make the relationship optional. And under researcher I would then
switch that to mandatory ?
Thanks Very Much
Owen McKerrow
WebMaster, emlab
http://emlab.uow.edu.au
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People who prefer typing to pointing then seem to prefer acronyms to
save typing :-)
-Denis Stanton, On people using Command Line Interfaces
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