Re: inheritance (EO Subclass) ?
Re: inheritance (EO Subclass) ?
- Subject: Re: inheritance (EO Subclass) ?
- From: Ramsey Gurley <email@hidden>
- Date: Sat, 19 Nov 2011 11:00:44 -0700
Agreed, this is not a case where you want inheritance.
On Nov 19, 2011, at 9:49 AM, Chuck Hill wrote:
>
> On 2011-11-19, at 8:30 AM, Theodore Petrosky wrote:
>
>> i guess i don't see how in your example a contact could be both an employee and a vendor and a media rep
>
> They can't that is the point of inheritance. A Dog can be a Mammal, but it can't be a Cat or a Rat (well Chihuahuas excepted). This is not a valid use of inheritance. EOF will not allow this. Look at the Role pattern.
A good link Chuck pointed to in an earlier discussion on this topic.
http://objectdiscovery.com/solutions/publications/roles/index.html
>
>
>> it seems to me that to use a contactType column, limits the contact to one and only one subclass
>
> Yes, that is absolutely required. This and only this is a correct use of inheritance:
> http://en.wikipedia.org/wiki/Liskov_substitution_principle
>
>
>> my method lets a contact belong to many different subclasses. I was questioning if this approach was 'good' or was I boxing myself into a corner that would bite me later.
>
> EOF is going to explode!
>
>
> Chuck
>
>
>> --- On Sat, 11/19/11, Paul Yu <email@hidden> wrote:
>>
>>> From: Paul Yu <email@hidden>
>>> Subject: Re: inheritance (EO Subclass) ?
>>> To: "Theodore Petrosky" <email@hidden>
>>> Cc: email@hidden
>>> Date: Saturday, November 19, 2011, 9:42 AM
>>> Ted
>>>
>>> I'm no expert on inheritance, but typically the setup
>>> should be
>>>
>>> Contact (Parent class) with a idContactType, marked as
>>> Abstract
>>> ContactType (1, Employee; 2, Vendor; 3, Media)
>>> Employee (Parent = Contact, Qualifier idContactType = 1)
>>> VendorContact (Parent = Contact, Qualifier idContactType =
>>> 2)
>>> MediaContact (Parent = Contact, Qualifier idContactType =
>>> 3)
>>>
>>> Then from your
>>> Company EO your relationship would be to Employee EO.
>>>
>>> Your fetches would be
>>>
>>> vendors = VendorContact.fetchVendorContact(ed,
>>> VendorContact.SOME_INTERESTING.eq(someValue), null);
>>>
>>> The type qualifier would be taken care of for you...
>>>
>>> Paul
>>> On Nov 19, 2011, at 9:00 AM, Theodore Petrosky wrote:
>>>
>>>> I am learning about subclassing EOs.
>>>>
>>>> I have an entity; Contact
>>>>
>>>> and three subclasses Employee, VendorContact,
>>> MediaContact
>>>>
>>>> the qualifiers are: isEmployee (bool)
>>> isVendorContact (bool) isMediaContact (bool)
>>>>
>>>> ie:
>>>> isEmployee <> 0
>>>> isVendorContact <> 0
>>>> isMediaContact <> 0
>>>>
>>>> testbed=# select * from t_contact;
>>>> c_first_name | c_last_name | id | c_is_vendor_contact | c_is_media_contact | c_is_employee
>>>> --------------+-------------+----+---------------------+--------------------+---------------
>>>> Ted | Petrosky | 1 | t | t | f
>>>> Bill | Simpson | 2 | t | t | t
>>>> Harold | Wall | 3 | f | t | t
>>>>
>>>> so I set up a test page simple with ordered lists
>>> wrapped in WOReps
>>>>
>>>> and queried the backend to populate the NSArrays:
>>>>
>>>> theEC = ERXEC.newEditingContext();
>>>>
>>>> vendors = VendorContact.fetchVendorContacts(theEC,
>>> VendorContact.IS_VENDOR_CONTACT.eq(true), null);
>>>> employees =
>>> CompanyEmployee.fetchCompanyEmployees(theEC,
>>> CompanyEmployee.IS_EMPLOYEE.eq(true), null);
>>>> mediaContacts = MediaContact.fetchMediaContacts(theEC,
>>> MediaContact.IS_MEDIA_CONTACT.eq(true), null);
>>>>
>>>> System.out.println("Media List " + mediaContacts);
>>>> System.out.println("Employees List " + employees);
>>>> System.out.println("Vendor List " + vendors);
>>>>
>>>> After I ran my app it barfed at me:
>>>>
>>>> Error:
>>> java.lang.IllegalArgumentException: While trying to set the
>>> field "anEmployee" on an object of type
>>> com.eltek.components.Main we expected a
>>> com.eltek.model.CompanyEmployee but received a
>>> com.eltek.model.VendorContact with a value of
>>> <com.eltek.model.VendorContact pk:"1">. This often
>>> happens if you forget to use a formatter.
>>>>
>>>> Now I understand that I can not fetch these entities
>>> in a single EC as any contact could be a member of any or
>>> all subclasses.
>>>>
>>>> Did I miss something (a property maybe [since
>>> everything is a property]) or must I use multiple ECs in
>>> this case? Obviously, that was my solution, set up a
>>> different EC for each subclass. Then all is well (but is
>>> it?).
>>>>
>>>> Ted
>>>>
>>>> _______________________________________________
>>>> Do not post admin requests to the list. They will be
>>> ignored.
>>>> Webobjects-dev mailing list (email@hidden)
>>>> Help/Unsubscribe/Update your Subscription:
>>>>
>>>> This email sent to email@hidden
>>>
>>>
>> _______________________________________________
>> Do not post admin requests to the list. They will be ignored.
>> Webobjects-dev mailing list (email@hidden)
>> Help/Unsubscribe/Update your Subscription:
>>
>> This email sent to email@hidden
>
> --
> Chuck Hill Senior Consultant / VP Development
>
> Practical WebObjects - for developers who want to increase their overall knowledge of WebObjects or who are trying to solve specific problems.
> http://www.global-village.net/products/practical_webobjects
>
>
>
>
>
>
>
> _______________________________________________
> Do not post admin requests to the list. They will be ignored.
> Webobjects-dev mailing list (email@hidden)
> Help/Unsubscribe/Update your Subscription:
>
> This email sent to email@hidden
Attachment:
smime.p7s
Description: S/MIME cryptographic signature
_______________________________________________
Do not post admin requests to the list. They will be ignored.
Webobjects-dev mailing list (email@hidden)
Help/Unsubscribe/Update your Subscription:
This email sent to email@hidden