Re: [Modeling-users] One to Many Relationships

[Sebastien B. <sbi...@us...>]

    Hi Dennis,

  The problem is that you forgot to indicate in your model that it is a
to-many relationship, so the script reacts as if it was a to-one
relationship.  See section 2.5.5. in the User's Guide; a unbound to-many
relationship typically defines:

    multiplicityLowerBound='0'
    multiplicityUpperBound='*'

(in your case you got the default values, i.e. respectively '0' and 
 '1', defining a to-one relationship)


Please also note that there is currently nothing in the framework that
makes sure that your XML-models does not rely on defaults that have
changed between two releases (this is not the case for PyModels, which
defines a 'version' field for this very purpose, see section 2.4.4).
The reason why there is no such mechanism is that the xml model is not
supposed to rely on defaults... even if I fear that this is not said
at all in the User's Guide.

  It does NOT mean you should always specify every possible fields in
your xml model: it just means that you should be careful.  When in doubt,
you can easily have your model dumped in another xml model with all its
value defined:

   >>> from Modeling.Model import loadModel
   >>> model=loadModel('your_model.xml')
   >>> model.saveModelAsXMLFile('FULLY_QUALIFIED_MODEL.xml')

Just a little warning: be sure to give an other filename, or you'll
overwrite your own model!


-- Sébastien.


Kertis, Dennis wrote:
> I am trying to define a one-to-many relationship in XML.  However,
> I am getting the following error:
> 
> Object: Relationship Category.topics
> ------------------------------------
>  * Error(s):
>    - relationship is not mandatory but source attribute Category.id
>      is required
>
> Can anyone tell me the correct way to model a one-to-many with Modeling?
> My "many" table has a foreign key to the primary key of my "one" table,
> but modeling doesn't seem to like this.
>
> Below is a cutdown of my model.
> 
> <entity
>             name='Topic'>
>             <primaryKey attributeName='id'/>
>             <attribute 
>                   name='id'
>                   type='int'
>                   isRequired='1'/>
>             <attribute 
>                   name='categoryID'
>                   type='int'
>                   isRequired='1'/>
> </entity>
> <entity
>       name='Category'
> <primaryKey attributeName='id'/>
>       <attribute 
>                   name='id'
>                   type='int'
>                   isClassProperty='0' 
>                   isRequired='1'/>
>      <relation 
>                   name='topics'
>                   destinationEntity='Topic'>
>                   <join 
>                         sourceAttribute='id'
>                         destinationAttribute='categoryID'/>
> </relation>
> </entity>