Re: Limiting number of assignments in a many-to-many relationship
Re: Limiting number of assignments in a many-to-many relationship
- Subject: Re: Limiting number of assignments in a many-to-many relationship
- From: Steve Sharman <email@hidden>
- Date: Mon, 12 Jan 2004 23:26:19 +0000
Denis (and all others who have thoughtfully replied),
Perhaps I should elaborate a bit more to try and explain my reasoning.
The reason that I've used many-to-many rather than a standard
one-to-many is that organisation (and person for that matter) will
participate in many other relationships, for example:
Many persons can be assigned to an organisation
Many positions can be assigned to an organisation
Many email addresses can be assigned to an organisation
As I understand it, that would mean that I would have one-to-many
relationships from person to organisation, from position to
organisation and from email address to organisation. I didn't think
that this was possible (or the right way to do things) in EOF. If I'm
wrong, then great - I've learned something tonight. If not, what would
you say is the best way to do what I need to do?
Best regards,
-- Steve
On 12 Jan 2004, at 21:16, Denis Stanton wrote:
Steve
This seems like a standard one-to-many relationship. Very easy. Why
are you thinking of implementing it as a many-to-many (much more
difficult) and then artificially restricting one of the "manies" to a
single item?
Surely you just need to add a foreign key to person, to point to
organisation, and then connect the two by dragging a link in EOM to
generate the "persons" relationship in organisation.
Denis
On Tuesday, January 13, 2004, at 09:49 AM, Steve Sharman wrote:
Happy New Year to all on the list.
I have a fairly simple question. In my application, I've implemented
a many to many relationship between two objects person and position -
with the obvious implication that each person may be assigned to one
or more position. I want to implement a similar relationship to
reflect the situation:
- There are many persons
- There are many organisations
- Many persons can be assigned to an organisation
- A person can be assigned to one and only one organisation
The way that I thought of approaching this was to implement a
many-to-many relationship in the usual way between person and
organisation, but implement a restriction at the Java level that
would ensure that a given person was assigned to only one
organisation at a time. Is this the best way to approach this
requirement, and does anyone have any pointers as to how it can be
most efficiently implemented?
Thanks in advance for your advice,
-- Steve
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