Hello,
We've been making good progress with using GeoServer's App-Schema
extension to map a PostGIS database to a GMLAS, however we are now
having difficulty with defining an App-Schema mapping that makes use of
a join table. We'd be very grateful if someone could provide us
assistance with the following problem:
I have in my PostGIS database two tables called "my_feature" and
"link_table". The columns and data that make up these two tables are
given below:
Table "my_feature"
pk_id name
1 "Feature1"
2 "Feature2"
3 "Feature3"
Table "join_table"
fk_my_feature feature_data (integer)
1 1
2 2
2 3
3 4
3 5
3 6
The GML Application Schema that I am mapping to contains a complex type
"MyFeatureType", with the following properties:
<xs:element name="featureName" type="xs:string"/>
<xs:element name="featureData" type="xs:integer" minOccurs="0"
maxOccurs="unbounded"/>
As you can see, the featureData element can have multiple values - what
I am attempting to achieve is to join the "my_feature" and "join_table"
tables where pk_id = fk_my_feature. This will give me all of the
feature_data values for each feature. As such, I want to obtain a WFS
response when I query for all the "MyFeatures" similar to the following:
<wfs:member>
<MyFeature gml:id="1">
<featureName>"Feature1"</featureName>
<featureData>1</featureData>
</MyFeature>
</wfs:member>
<wfs:member>
<MyFeature gml:id="2">
<featureName>"Feature2"</featureName>
<featureData>2</featureData>
<featureData>3</featureData>
</MyFeature>
</wfs:member>
<wfs:member>
<MyFeature gml:id="3">
<featureName>"Feature3"</featureName>
<featureData>4</featureData>
<featureData>5</featureData>
<featureData>6</featureData>
</MyFeature>
</wfs:member>
My question is, how should I define my FeatureTypeMapping in my
App-Schema mapping file in order to produce the above result?
I've read in the documentation that "Feature chaining" may be used to
achieve this effect, but the examples in the tutorials appear to require
at least two features to be defined in the GMLAS. However, in my
scenario, I only have one feature type to map against ("MyFeatureType")
- the join_table does not have a corresponding feature type defined in
the GMLAS.
Can you also please advise if this scenario requires my tables to be
denormalised prior to the App-Schema mapping, and what the performance
implications of this might be, i.e:
Table "denormalised_table"
pk_id feature_name feature_data
1 "Feature A" 1
2 "Feature B" 2
2 "Feature B" 3
3 "Feature C" 4
3 "Feature C" 5
3 "Feature C" 6
Any assistance will be greatly appreciated :-)
Best Regards,
Ryan
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