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# many-many relationship

Posted on 2011-09-06
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I was trying to understand about many-many relationship. Say many customers have many phone numbers. How does it impact single customer. Like Single customer always have many phones(like home phone, mobile phone, office phone number etc ). Then that becomes one-many relationship right not many-many. Thanks in advance
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Question by:gudii9
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for_yan earned 1000 total points
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check example this example:

say one stock can belong to many categories - say commodities, big company

and one category cabn conating many duifferent stocks

look at details here:

http://www.mkyong.com/hibernate/hibernate-many-to-many-relationship-example/
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CEHJ earned 1000 total points
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>>
Like Single customer always have many phones(like home phone, mobile phone, office phone number etc ). Then that becomes one-many relationship right not many-many.
>>

When you think about N-N relationships, it's helpful to think of database use cases.
In a situation like you mention above (customer, phones and many-many), the following use cases spring to mind:

1. Given a customer, find their phone number(s)
2. Given a phone number, find to which customer(s) it belongs

The second one is made possible by many to many. Phone number X could belong to customers Y or Z, because Y and Z live at the same address
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