Re: A better way so save datasets with relations?

Hi Jerry,

thanks a lot! WO is so easy that I need some time to deal with it :-)
I never thought of the possibility to make the foreign key in the  
table NOT a class attribute.
Thanks for the advice with the naming conventions. I renamed the  
classes.

Best regards,

Helmut

Am 04.01.2007 um 19:06 schrieb Jerry W. Walker:

> Hi, Helmut,
>
> First, I would suggest renaming your classes to Category and  
> Keyword, that is, without the "EO" prefix which should be reserved  
> for classes defined in the EOFrameworks.
>
> Pay careful attention to the first four columns in EOModeler's  
> table mode when an entity is selected for editing. If we label the  
> four columns as follows: <key>, <diamond>, <lock>, and <0>, I would  
> suggest defining your two entities as follows:
>
>                    <key>  <diamond> <lock> <0>
> Category
>     id                
> X                                               (primary key)
>     category                     X            X                  
> (varchar)
>
> Keyword
>     id                
> X                                               (primary key)
>     keyword                     X            X                  
> (varchar)
>     fiCategory                                 X                  
> (id, foreign index of the category)
>     category                     X            X                  
> (relation, which defines an 1:1 relation between  
> EOKeyword.fiCategory and EOCategory.id)
>
> Be sure that the category attribute of Keyword is defined as a  
> relation, that is, when EOModeler is in Table mode, it is displayed  
> under the lower "Keyword Relationships" section of the Table Mode  
> view rather than the upper "Keyword Attributes" section.
>
> If you've defined your two entities as above, then, When you want  
> to save a new Keyword, your code should look as follows:
>
>      EOEditingContext ec = session().defaultEditingContext(); //  
> retrieve the EC
>      Category categoryObject; // Assume we already have one of  
> these and that it was retrieved, or created, in the ec  
> EOEditingContext
>
>      Keyword newKeyword = (Keyword) 
> EOUtilities.createAndInsertInstance(ec, "Keyword"); // create and  
> insert a new instance of Keyword
>      newKeyword.takeValueForKey(newkeyword, "keyword"); // set the  
> keyword with a value from a web form
>      newKeyword.addObjectToBothSidesOfRelationshipWithKey 
> (categoryObject, "category");
>
> In particular, note that the primary keys for both EOs are NOT  
> class properties, and therefore, are not visible in your Java code.  
> Let EOF take care of the keys for you. It tends to be very good at  
> that and often does less well if you're interfering with it's  
> efforts.  :-)
>
> If the code, as I've presented it, raises an exception, please copy  
> the stack trace when you ask about it. Presuming that you've got a  
> legitimate categoryObject at the start of the code, that is, one  
> that was retrieved or created in ec, then it should just work.
>
> Regards,
> Jerry
>
>
> On Jan 4, 2007, at 12:31 PM, Helmut Schottmüller wrote:
>
>> Hi Group,
>>
>> again a rookie question :-( Sorry for that.
>>
>> I have created two entities in my application:
>>
>> EOCategory (which stores a category) and
>> EOKeyword (which stores a keyword of a given category)
>>
>> EOCategory {
>>   id (primary key)
>>   category (varchar)
>> }
>>
>> EOKeyword {
>>   id (primary key)
>>   keyword (varchar)
>>   fiCategory (id, foreign index of the category)
>>   category (relation, which defines an 1:1 relation between  
>> EOKeyword.fiCategory and EOCategory.id)
>> }
>>
>> so far I think this is the correct way to define a relation in  
>> EOModeler.
>>
>> When I want to save a new Keyword I have to do the following:
>>
>> EOEditingContext ec = session().defaultEditingContext(); //  
>> retrieve the EC
>> EOKeyword newKeyword = (EOKeyword) 
>> EOUtilities.createAndInsertInstance(ec, "EOKeyword"); // create  
>> and insert a new instance of EOKeyword
>> newKeyword.takeValueForKey(newkeyword, "keyword"); // set the  
>> keyword with a value from a web form
>> NSDictionary result = EOUtilities.primaryKeyForObject(ec,  
>> categoryObject); // retreive the primary key of the related  
>> category object
>> int pkey = ((Integer)result.objectForKey("id")).intValue(); //  
>> retreive the primary key of the related category object
>> newKeyword.takeValueForKey(new Integer(pkey), "fiCategory"); //  
>> set the foreign index in the EOKeyword instance
>> newKeyword.addObjectToBothSidesOfRelationshipWithKey 
>> (categoryObject, "category"); // add the relation to the EOKeyword  
>> instance
>>
>>
>> In the beginning I thought that it should be sufficient to set the  
>> keyword and to use addObjectToBothSidesOfRelationshipWithKey to  
>> set the relation because I would expect, that  
>> addObjectToBothSidesOfRelationshipWithKey takes care of the  
>> foreign index attribute of the entity. But this didn't work. I  
>> always got an exception which occured during the validation of the  
>> foreign index.
>>
>> Is this the right way to save a dataset with a relation to the  
>> database? I doubt that.
>> Could someone give me a clue what I can do better?
>>
>> Thanks in advance,
>>
>> Helmut_______________________________________________
>> WebObjects-dev mailing list
>> [email protected]
>> http://www.omnigroup.com/mailman/listinfo/webobjects-dev
>
>
> --
> __ Jerry W. Walker,
>    WebObjects Developer/Instructor for High Performance Industrial  
> Strength Internet Enabled Systems
>
>     [email protected]
>     203 278-4085        office
>
>
>