Re: Many-to-Many inside same Entity
Re: Many-to-Many inside same Entity
- Subject: Re: Many-to-Many inside same Entity
- From: Louis Demers <email@hidden>
- Date: Tue, 07 Feb 2006 22:50:20 -0500
At 1:20 PM +0100 2006/02/07, Wolfram Stebel wrote:
Am 07.02.2006 12:31 Uhr schrieb "Amedeo Mantica" unter
<email@hidden>:
Hi, a question... how to implement this:
Products entity...
> some product can be related to many other products...
..
But one thing: you have to maintain the join table manually!
I will send you an extract of the data model with separata post.
I've just been working on this type of application for the past few
weeks, implementing the eomodel first.
I did create a "many to many" reflexive relationship manually.
including flatten relationship. I've only done the eomodel so far,
no code ot wocomponents.
So i'm a little puzzled by your statement that the join has to be
maintainned manually ? Exactly what do you mean, how complicated is
it ?
I would be interested in the extract you mentionned below.
Also,
At 5:06 PM -0500 2006/02/07, Robert Walker wrote:
Amedeo,
What you have here is a design pattern known as a "Bill of Material."
...
You will need an exposed join table (so no flattening of the
many-to-many can be used). At minimum the join table will need an
"exposed" attribute to indicate the quantity of each component part
used in the product being built.
Part <---->> ComponentAssembly <<---- Part
I avoided this by including the number attribute in the part entity
so my join table is "pure" and therforer did not expect to expose it.
I suppose that the the "no flattening" declaratio nabove stands only
when the join taible include attrivutes that need to be exposed.
I'll have to reflect on the suitability of placing the count
attribute with the part ! You may have exposed a problem i hadn't ran
through my "paper simulations".
I'm curious to hear what particular diffculties exists with reflexive
many-to-many, so i can correct my approach early in the design.
--
Louis Demers ing.
email@hidden
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