Hi all,
Recently I have been dealing with some use cases that require the ability to inject some native
filters,
specific for each feature type and non static over time, to the final native query build by GeoTools
and
send to the data store.
For example, the content of a feature type is partially controlled by an external service who
provides a non
static native query (the request changes over time) that filters the content
that should be show.
Another use case is a complex authorization rules system where the
authorization rules are SQL
expressions that need to be append to the final SQL WHERE clause build by
GeoTools, the system
provides SQL expressions for different databases (Oracle, PostgreSQL, MySQL,
etc ...).
Most of the native filters of this use cases are quite complex and can't be
translated to OGC filters.
Since we have a pattern here that can be applied to several use cases and data stores I have think
about
an approach that would allow extensions, external code, etc ... to inject the necessary native
filter(s)
and allow data stores implementations to handle those native filters in an
harmonized way.
I have come up with the idea of a new filter named /NativeFilter/:
* this filter will NOT be directly usable by the final users, for example in
WFS requests
* if any code try to evaluate it in memory an exception will be throw
* it will not break any API and data stores will be free to implement is
support has needed
* it will have a method getNative() that will return a String containing the
native filter
A new default method would need to be added to the /FilterVisitor/ interface
and a default
implementation would need to be added to /AsbtractFilterVisitor and
DuplicatingFilterVisitor /
classes (like for any other filter).
The data store who wants to supports this filter will need to extends it custom
visitor, for example,
for relational databases we only need to add a new visit method to
/FilterToSQL/ visitor.
This gives the necessary flexibility for third party code (codes that use
GeoTools) to inject native
filters without any specific extension points or cumbersome handling. It is
also worth notice unless
some code is using native filters this will have no impact on other usages.
Any thoughts on this ? Objections ?
King regards,
Nuno Oliveira
--
Regards,
Nuno Oliveira
==
GeoServer Professional Services from the experts! Visit http://goo.gl/it488V
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==
Nuno Miguel Carvalho Oliveira
@nmcoliveira
Software Engineer
GeoSolutions S.A.S.
Via di Montramito 3/A
55054 Massarosa (LU)
Italy
phone: +39 0584 962313
fax: +39 0584 1660272
http://www.geo-solutions.it
http://twitter.com/geosolutions_it
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