[Zope3-dev] default and required analysis

[Steve Alexander]

Jim Fulton wrote:
> 
> Based on Martijn's analysis and Steve's comments, I proposed the following:
> 
> - If a field is in the schema, objects that implement the schema must
>   have a corresponding property implementing the field.

That's a very strong statement. I don't disagree with it. It just feels 
like it is stronger that it needs to be.


> - If a field is required, then all values of properties implementing the 
>   field must satisfy the field's constraints.
> 
> - If a field is not required, then a property implementing a field may 
>   have a field-defined missing value that does not satisfy the field's 
>   constraints.
>   The default missing value will be None, but fields may provide 
>   different missing values.

Can I clarify this as "A field may provide a missing value" ?

That is, there is only one 'missing' value per field, and this is None 
by default.


> - Fields may define default values. An application (like a form) can use 
>   this default value to provide a value when a value is needed and no other 
>   value is available.  The default value may be the field-defined missing
 >   value or a value that satisfies the field's constraints.
> 
>   If a field is required and the default value does not satisfy the field's
>   constraints, then the default value cannot be used to provide a value 
>   for a property implementing the field.

I am +1 on the whole proposal.

--
Steve Alexander