Re: inheritance (EO Subclass) ?
Re: inheritance (EO Subclass) ?
- Subject: Re: inheritance (EO Subclass) ?
- From: Chuck Hill <email@hidden>
- Date: Sat, 19 Nov 2011 08:49:09 -0800
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.
> 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
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