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Re: Many-to-many w/ one entity
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Re: Many-to-many w/ one entity


  • Subject: Re: Many-to-many w/ one entity
  • From: Clark Mueller <email@hidden>
  • Date: Sun, 23 Jul 2006 21:44:19 -0500

Mark,

Thanks, that worked perfectly! That is exactly what I needed, I was having trouble wrapping my head around how that would be put together. :-)

Thanks,
Clark

On 23 Jul 06, at 9:04 AM, Mark Morris wrote:

Hello Clark,

You can manually model this almost the same way you would a many-to- many involving two tables.

(Names are examples only. ;-) First create the RELATED_PRODUCT table with just PRODUCT_ID and RELATED_PRODUCT_ID columns. Make a to-many join from PRODUCT to RELATED_PRODUCT using PRODUCT_ID from both tables. Then make a to-one join from RELATED_PRODUCT's RELATED_PRODUCT_ID to PRODUCT's PRODUCT_ID. Now you can flatten that into a "relatedProducts" relationship starting and ending at PRODUCT. (Remove the diamond in EOModeler from the original relationships.)

The odd thing about this is that the inverse relationship isn't that useful. If you modeled it, it would basically be saying, "These are the products that consider me a related product." But it would quickly get confusing if you tried to use it! So if two products are related to each other, just add each to the other's "relatedProducts" relationship.

Hope this helps!

Regards,
Mark

On Jul 22, 2006, at 10:20 PM, Clark Mueller wrote:

All,

I'm trying to create a many-to-many relationship with a single entity. Essentially, what I'm doing is trying to show "related products" for a Product entity. EOModeler certainly won't model this one. I have tried to model it myself (both in OpenBase directly, and in EOModeler) mimicking the way EOModeler builds one with two entities... but this breaks down a little bit when I try to sort out the relationships from the intermediate table, so I haven't had a lot of success. I am hoping that's just because I've never done it before, and that someone can talk me through it. :-)

I've also seen this implemented in some cases by adding an attribute (e.g. "related_products") to the entity containing data like this:

pk_1|pk_2|pk_3

pointing to the related items. But I am sure that this is a pain in the butt to use with EO, to actually fetch those related objects.

Can someone suggest the best way to model this relationship?

Thanks & regards,
Clark


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References: 
 >Many-to-many w/ one entity (From: Clark Mueller <email@hidden>)
 >Re: Many-to-many w/ one entity (From: Mark Morris <email@hidden>)

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