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Re: Core Data: unidirectional relationships
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Re: Core Data: unidirectional relationships


  • Subject: Re: Core Data: unidirectional relationships
  • From: William Turner <email@hidden>
  • Date: Wed, 13 Feb 2008 09:52:23 -0800

Hi Ruotger,

Another alternative that might work for you is to add a "title" (string) attribute to Employee and fetched properties to the Department for each of headOfDepartment, viceHeadOfDepartment, pointyHairedBoss, and dilbert, with their predicates being title=="Head", title=="ViceHead", etc.

You can read more about using fetched properties to represent one-way relationships near the end of http://developer.apple.com/documentation/Cocoa/Conceptual/CoreData/Articles/cdRelationships.html

Wil

On Feb 13, 2008, at 9:29 AM, Brian Williams wrote:

I have had to deal with this also. I think that the best solution is to just
have those empty back links and accept the clutter. You could also have
subclasses of employee, but i am sure that would cause other problems.


On 2/13/08, Ruotger Skupin <email@hidden> wrote:

Hi,

consider the following example (that what I would like to model):

Entity: Department
Attributes: ...whatever...
Relationships:
headOfDepartment --> Employee
viceHeadOfDepartment --> Employee
pointyHairedBoss -->
dilbert -->
other Employees -->>


Entity: Employee Attributes: ...whatever... Relationships: department --> Department


Every Employee is only in one Department. The Department has (and needs) four special Employees (head, vice head, pointy haired boss, dilbert). Turns out that it is impossible to model this with bidirectional relationships if you don't want to model it like that:

Entity: Employee
Attributes: ...whatever...
Relationships:
departmentImHeadOf --> Department
departmentImViceHeadOf --> Department
departmentImPointyHairedBossOf --> Department
departmentImDilbertOf --> Department
departmentOtherEmployeeOf --> Department


The other alternative is to model it with unidirectional relationship,
which is discouraged.


Can anyone gime some advice on this?

Ruotger

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  • Follow-Ups:
    • Re: Core Data: unidirectional relationships
      • From: Adam P Jenkins <email@hidden>
References: 
 >Core Data: unidirectional relationships (From: Ruotger Skupin <email@hidden>)
 >Re: Core Data: unidirectional relationships (From: "Brian Williams" <email@hidden>)

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