Author: | Sean Gillies |
---|---|
Revision: | $Revision: 8278 $ |
Date: | $Date: 2008-12-23 13:34:31 -0800 (Tue, 23 Dec 2008) $ |
All examples in this document refer to the mapfile and testing layers distributed with MapServer 4.2+ and found under mapserver/tests.
All examples will use a pseudocode that is consistent with the language independent API reference. Each line is a statement. For object attributes and methods we use the dot, ‘.’, operator. Creation and deletion of objects will be indicated by ‘new’ and ‘del’ keywords. Other than that, the pseudocode looks a lot like Python.
Map layers can be queried to select features using spatial query methods or the attribute query method. Ignoring for the moment whether we are executing a spatial or attribute query, results are obtained like so:
layer.query() # not an actual method!
results = layer.getResults()
In the case of a failed query or query with zero results, ‘getResults’ returns NULL.
Individual members of the query results are obtained like:
... # continued
if results:
for i in range(results.numresults): # iterate over results
result = results.getResult(i)
This result object is a handle, of sorts, for a feature of the layer, having ‘shapeindex’ and ‘tileindex’ attributes that can be used as arguments to ‘getFeature’.
The previous example code can now be extended to the case of obtaining all queried features:
layer.query()
results = layer.getResults()
if results:
# open layer in preparation of reading shapes
layer.open()
for i in range(results.numresults):
result = results.getResult(i)
layer.getFeature(result.shapeindex, result.tileindex)
... # do something with this feature
# Close when done
layer.close()
Scripts using the 4.2 API can continue to access query result members through layer methods:
for i in range(layer.getNumResults()):
result = layer.getResult(0)
but should adopt the new API for use in new work.
queryByAttributes()