[Please keep discussions on the list]
On 01/08/13 09:33, Ing. Pierluigi De Rosa wrote:
Il giorno mer, 31/07/2013 alle 14.10 +0200, Moritz Lennert ha scritto:
On 31/07/13 10:27, Ing. Pierluigi De Rosa wrote:
Dear all,
I know this problem could be sorted easily using statialdb but I'm
asking if is possible to do the same think in grass.
I have a vector layer that store db in posgtres.
So GRASS vector layer with attributes in PostgreSQL ?
Yes, exactly.
I'm able to extract
(v.extract) vector feature from this using sql query based on data
stored into an other table 2 into the postgres db.
The question is that if I change a value into the table 2 the vector
extracted does not reflect this changes but I have to run again
v.extract
Dou you have any suggestion?
Depending on the module that you use to treat the result of the
v.extract, you might be able to not do a v.extract at all, but just use
the 'where' parameter of the module (MarkusM has started integrating
that parameter in more vector modules in GRASS 7 [1])
here below is the code I'm using
v.extract -t input=layer_input output=frane_da_visitare type=area
where="cat in (select table1.cat from table2, table1 where
table2.idfrana = table1.idfrana) " --o
So, if I understand, as the v.extract is based on a where sql I don't
have to run this command if some changes in table2 appears?
No. v.extract creates a new vector map that will not change if you
change table2 after having run v.extract.
What I meant is : what do you do with frane_da_visitare after having run
v.extract ? If the modules you use to treat the data afterwards have a
where parameter, you could skip v.extract and just use your SQL in the
where clause of the respective modules.
If you can use the where parameter, the you can create a view in your
database connecting the attribut table of the map with your table 2,
then use v.db.connect to connect your map to that view and then use
'where' to work on the features that meet your criteria.
Yes, this is what I do now.
Actually, with your solution of 'cat in (select ...)' you don't even
need to create a view.
Moritz
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