[baseten-users] updating of SQL-views

[Patrick De Visschere]

Hello again,

Thanks for your suggestions, but first I'm still trying to find out  
what the limitations are of the automatic updating mechanism.

In the example I've mentioned there was 1 table (A) and a view (V) of  
that table. A contains a column which is calculated in postgresql.
As I've noticed this dependent column is not updated via the view V  
and I understand from your answer that this is indeed not implemented.
I was a little bit surprised because I have another example,  more  
complicated, where it works anyway.

Suppose I move the dependent column to a separate table (B) with a one- 
to-one between A and B and the view V now joining A and B.
In that case the dependent column of B is sometimes updated  
automatically.
I can only guess why it sometimes works but not always: apparently a  
one-to-one relationship is made  (I guess by the assistant) between  
the view V and one of the underlying tables (A and B). I guess that If  
this relationship is to the dependent table B, then it's updated; if  
it is to the main table A, it is not.
Does this make sense?
And if it does, is there a way to force one possibility over the other?

Regards,

P. De Visschere

On 9 Feb, 2010, at 12:37 AM, Tuukka Norri wrote:

> Hi and sorry about taking some time with this.
>
> Patrick De Visschere kirjoitti 30.1.2010 kello 15.37:
>> I have a single table and an SQL-view of that table; baseten is  
>> connected to the view and the required SQL-RULES are present.
>> - when I make changes in the table with pgAdmin, these are not  
>> shown in the Cocoa-views. This is probably normal since baseten is  
>> connected to the SQL-view. I enabled also the underlying table with  
>> the assistant but that makes no difference.
> Unfortunately the change notifications have been implemented in such  
> a way that changes in underlying tables won't currently be noticed.  
> We did experiment with cascading notifications but they turned out  
> to be more problematic than what they were worth.
>
>> - let's say that 1 column of the table is the sum of 2 other  
>> columns (the sum is calculated by PostgreSQL) ; when I make changes  
>> in the Cocoa-views then the  SQL-table is properly updated but the  
>> sum never shows up in the Cocoa-view although it's value is  
>> returned by the RETURNING clause in the SQL- view RULES.
> When updating views only the primary key values are fetched, so  
> changing the rule won't help.
>
>> - The view also contains a running-total; should this also be  
>> updated automatically by BaseTen in the Cocoa-views?
> I would expect that it won't be updated.
>
> I can only offer some workarounds to the problem. If the calculation  
> is simple, you could write a custom getter with a matching  
> +keyPathsForValuesAffecting<Key> method. You could also use key- 
> value coding operators [1].  
> Another 
>                                                                     
> option is to use key-value observing to get a notification when a  
> column gets updated and call -[BXDatabaseObject faultKey:] with the  
> name of the column that contains the calculation as the argument  
> when that happens.
>
> [1] http://developer.apple.com/mac/library/documentation/cocoa/Conceptual/KeyValueCoding/Concepts/ArrayOperators.html
> -- 
> Best regards,
> Tuukka Norri
> MK&C
>
>
>
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