Hi,
while working on the GeoServer synchronisation problem
I stumbled into what seems a serious limitation of the
Geotools datastore design.
In particular I need to insert features into a database
whose feature id is provided by the user and should be
maintained as-is. In the synch case the fid is a UUID
generated on another node for a newly inserted feature,
and of course to keep the net in synch all nodes must
use the same identity.
For that particular case I worked around the issue in
the versioning data store by leveraging some knowledge
of the internal implementation, by knowing that the
feature returned from the writer is a MutableFIDFeature
one [1]
That is old JDBC code, and internally the custom UUID FID
mapper first tries to unpack the primary key, checking
if it's a valid UUID, if so it reuses the value,
otherwise it generates a new one.
Just today I stumbled into a user having the same need against
the new JDBC data stores.
I'm wondering if/how we can generalize a bit more this behavior,
also under the consideration that the WFS standard itself
allows the primary keys to be both generated or assigned
in transactions [2]
Of course one way is to replicate sort of the same trick
for JDBCFeatureStore, leveraging the knowledge of the
feature returned by the writer to stick a FID into it,
and then change JDBCDataStore.getNextValue() so that it
also takes the current Feature and tries to unpack the
primary key instead of blindly trying to generate a new
value.
This would also be an acceptable solution to me btw,
and I guess it would cover 90% of what is needed:
shapefile datastore cannot accept user provided pks,
the only other one I can think of that would need
to use assigned values is probably the WFS data store
one (and maybe the SDE one? not sure).
Opinions?
Cheers
Andrea
[1] -----------------------------------------------------
public List<FeatureId> addFeatures(
FeatureCollection<SimpleFeatureType, SimpleFeature>
collection) throws IOException {
List<FeatureId> addedFids = new LinkedList<FeatureId>();
String typeName = getSchema().getTypeName();
SimpleFeature feature = null;
SimpleFeature newFeature;
FeatureWriter<SimpleFeatureType, SimpleFeature> writer =
getDataStore()
.getFeatureWriterAppend(typeName, getTransaction());
Iterator iterator = collection.iterator();
try {
while (iterator.hasNext()) {
feature = (SimpleFeature) iterator.next();
newFeature = (SimpleFeature) writer.next();
try {
newFeature.setAttributes(feature.getAttributes());
} catch (Exception writeProblem) {
throw new DataSourceException("Could not create " +
typeName
+ " out of provided feature: " +
feature.getID(), writeProblem);
}
// preserve the FID, it could come from another node
((MutableFIDFeature) newFeature).setID(feature.getID());
writer.write();
addedFids.add(newFeature.getIdentifier());
}
} finally {
collection.close(iterator);
writer.close();
}
return addedFids;
}
[2] -----------------------------------------------------
<xsd:simpleType name="IdentifierGenerationOptionType">
<xsd:restriction base="xsd:string">
<xsd:enumeration value="UseExisting">
<xsd:annotation>
<xsd:documentation>
The UseExsiting value indicates that WFS should not
generate a new feature identifier for the feature
being inserted into the repositry. Instead, the WFS
should use the identifier encoded if the feature.
If a duplicate exists then the WFS should raise an
exception.
</xsd:documentation>
</xsd:annotation>
</xsd:enumeration>
<xsd:enumeration value="ReplaceDuplicate">
<xsd:annotation>
<xsd:documentation>
The ReplaceDuplicate value indicates that WFS should
not generate a new feature identifier for the feature
being inserted into the repositry. Instead, the WFS
should use the identifier encoded if the feature.
If a duplicate exists then the WFS should replace the
existing feature instance with the one encoded in the
Insert action.
</xsd:documentation>
</xsd:annotation>
</xsd:enumeration>
<xsd:enumeration value="GenerateNew">
<xsd:annotation>
<xsd:documentation>
The GenerateNew value indicates that WFS should
generate a new unique feature identifier for the
feature being inserted into the repositry.
</xsd:documentation>
</xsd:annotation>
</xsd:enumeration>
</xsd:restriction>
</xsd:simpleType>
--
Andrea Aime
OpenGeo - http://opengeo.org
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