[fdo-internals] SQLite provider issues

Wed Jul 28 14:27:44 EDT 2010

Views from sqlite are exposed as fdo classes right now, so yes fdo
sqlite suports views from sqlite.
But there are at least three bugs in fdo sqlite right now regarding
views which makes them unusable:

1. If underlaying table is changed  that is not seen in view. That was
reported by my colleagues. Haven't yet looked what is reason here, I
assume dual connection which is used in provider (perhaps combined
with some caching)

2. FDO class generated from view is marked as non-writable. That is
wrong assumption that views are not updatble in sqlite. Provider would
just leave writable==true ( as it was in 3.4 version)

3. FDO class generated from view is marked as computed which is wrong,
as I describe in emails before.

Some of those bugs are introduced after 3.4 , in changeset which
number I wrote in email before.

Haris

On Wed, Jul 28, 2010 at 8:08 PM, Greg Boone <greg.boone at autodesk.com> wrote:
> Before we change anything, I would like further clarification on the view issue. It seems partially supported at the least. What is the intent here. Are we intending to support read from views? Should a user be attempting any action other than read?
>
> To me, if we support read from views, the update to the underlying table not being reflected in the view is a bug.
>
> Greg
>
> -----Original Message-----
> From: fdo-internals-bounces at lists.osgeo.org [mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Haris Kurtagic
> Sent: Wednesday, July 28, 2010 1:03 PM
> To: FDO Internals Mail List
> Subject: Re: [fdo-internals] SQLite provider issues
>
> I don't understand your answers.
>
> If it is ok , I will fix sqlite so views are not marked as not
> computed and non-writable.
>
> Haris
>
> On Wed, Jul 28, 2010 at 4:17 PM, Romica Dascalescu
> <Romica.Dascalescu at autodesk.com> wrote:
>> SQLite provider 3.5 don't really supports views.
>>
>> Romy
>> -----Original Message-----
>> From: fdo-internals-bounces at lists.osgeo.org [mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Romica Dascalescu
>> Sent: Wednesday, July 28, 2010 10:16 AM
>> To: FDO Internals Mail List
>> Subject: RE: [fdo-internals] SQLite provider issues
>>
>> Views are cached in FDO 3.5 and are not updated when class gets updated.
>>
>> Romy.
>> -----Original Message-----
>> From: fdo-internals-bounces at lists.osgeo.org [mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Haris Kurtagic
>> Sent: Wednesday, July 28, 2010 10:14 AM
>> To: FDO Internals Mail List
>> Subject: Re: [fdo-internals] SQLite provider issues
>>
>> Hi Romica
>>
>> 1) Computed class as described in FDO
>>     "Computed classes cannot be made persistent or added to FDO
>> schema. The computed classes are used as a transient classes that can
>> be returned by a feature or data reader."
>>     I thin it is pretty clear from above that it is bug in sqlite provider.
>>
>> 2) It is not limitation of provider but bug.
>>    If sqlte contains updatable views they will be reported as
>> read-only buy provider. Proivder will wrongly limit sqlite.
>>
>>
>> 3) It seems even bigger problems with views (Simon is testing this).
>> If original table is updated view is not. Provider returns wrong
>> results. I suspect some issue with dual-connection nature of sqlite
>> provider and/or caching.
>>
>> If that will be case for non-sql providers, to update even for
>> non-writable classes, file would be updated trough provider which
>> would be wrong while provider said it is not updateble
>>
>>
>>
>>
>>
>> On Wed, Jul 28, 2010 at 3:48 PM, Romica Dascalescu
>> <Romica.Dascalescu at autodesk.com> wrote:
>>> Hi Haris,
>>>
>>> 1) SetIsComputed(), there is a thin line here since a view is a computed/generated class. Why this would be a problems in this case?
>>>
>>> 2) You can say this is a limitation of the provider and we cannot update views. However there is a way to update a view if Id of the view and geometry is from the same class and those are defined in (fdo) metadata (but this is in FDO 3.6 only).
>>> All the time SupporsWrite()=false for views and I don't see a problems since the provider is not meant to implement everything.
>>>
>>> SupporsWrite() will be false in case tythe file is read only and all classes will have this flag set to false. This flag should be checked by the application and take care of this otherwise exception will be thrown but only later at execute time.
>>>
>>> SQLite provider do not enforce too many things (starting with string length and ending with read-only flag), and in case an application ignore this flag and use a SQL commands to update database there is nothing provider will do, since provider will not parse the SQL! The sqlite engine for sure will throw an exception at execution time.
>>>
>>> Thanks,
>>> Romy.
>>>
>>> -----Original Message-----
>>> From: fdo-internals-bounces at lists.osgeo.org [mailto:fdo-internals-bounces at lists.osgeo.org] On Behalf Of Haris Kurtagic
>>> Sent: Wednesday, July 28, 2010 9:25 AM
>>> To: FDO Internals Mail List
>>> Subject: [fdo-internals] SQLite provider issues
>>>
>>> Hi,
>>>
>>> FDO Sqlite provider has changed in revision 4823 ( from 3.4 to 3.5 )
>>> regarding views in sqlite.
>>>
>>> I think it introduced two issues:
>>>
>>> 1. Provider will mark fdo class generated from view as computed
>>> "SetIsComputed(true)" which is wrong by fdo definition of computed
>>> class.
>>>
>>> 2. SupportsWrite is set to false - which is wrong. SQlite suports
>>> write to views when they have "instead of" trigger
>>>
>>>
>>> Also there is yet another problem of understanding what SupporsWrite
>>> means in FDO.
>>> Is it just informative or will enforce it.
>>> Right now, sqlite provider will pass trough update commands to sqlite
>>> even if provider marked some class as "doesn't support write".
>>> I think if class is marked as non-writable by provider shouldn't send
>>> update commands to underlaying storage.
>>>
>>> Haris
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