[mapguide-trac] #1464: The selection of a feature appears to be inefficient (too many server calls)

[MapGuide Open Source]

#1464: The selection of a feature appears to be inefficient (too many server
calls)
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   Reporter:  gabrimonfa   |       Owner:       
       Type:  defect       |      Status:  new  
   Priority:  low          |   Milestone:       
  Component:  AJAX Viewer  |     Version:  2.2.0
   Severity:  trivial      |    Keywords:       
External_id:               |  
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 I'm using mapguideOS 2.2beta, Basic Layout and PHP.

 in my application I need to have a function which selects a feature in the
 map.

 Looking at the Viewer API I would like to have found a function
 SetSelection(layer, sqlWhereClause) but the only suitable function
 appears to be SetSelectionXML(xmlSet) to be called on the mapFrame
 http://mapguide.osgeo.org/files/mapguide/docs/2.0/viewerapi.html#mapframe_setselectionxml

 This function needs a well-defined XML, complaint with
 FeatureSet-1.0.0.xsd, with the feature id encoded in BASE64, thus
 difficult to obtained without going through the API

 I made an AJAX call from a javascript function (let's call it
 'mySelectionJavascriptFunction()') to a PHP script (let's call it
 'mySelection.php') that constructs the XML starting from the layer and
 the id of the feature.
 This involves some calls to the Web API, that end with a
 MgSelection::ToXml();

 The obtained XML is then passed to SetSelectionXML and indeed all works.

 However, having a look to the webserver log and mapguide-apache log
 the procedure seems to need 3 calls to PHP pages.
 This are my findings:

 The SetSelectionXML(xmlSet) needs for its processing two distinct xmls:

 1. the input parameter 'xmlSet' that is used to produce the blue selection
 image
 2. another xml, 'xmlOut', needed to obtain and inject the selected
 feature properties into the Property Panel of the Viewer.

 The 'xmlOut' is produced calling the function SetSelection() that
 makes a request to a PHP page, setselection.php, that parses the xml
 to extract the layer and the feature id and produces 'xmlOut' (on a
 side note, it uses MgFeatureInformation->ToXml() that seems not
 present in the API documentation...).

 This 'xmlOut' is then passed to "ProcessFeatureInfo(xmlOut, false, 2)"
 that discards it (!!) and calls RequestSelectedFeatureProperties()
 which in turn call yet another PHP page, getselectedfeature.php that
 responds with a JSON object (let's call it 'resp') with the very same
 properties of the feature, that is then passed into a bunch of other
 javascript functions, starting with ProcessSelectedFeatureSet(resp),
 that are not interesting in this analysis.

 Javascript computation is not a problem, but too many round-trip calls
 to PHP pages on the server affects server performance.
 Moreover, each PHP script makes a lot of routine calls to the API,
 basically to verify user credential, create the services, open the
 runtime map, iterating through the layers and so on.

 In summary, each selection involves 3 calls to PHP pages (the symbol
 => means a call to a PHP page, the symbol ----> means its return
 value, followed by an example instance):

 1. mySelectionJavascriptFunction() => mySelection.php ----> xmlSet

 <?xml version="1.0" encoding="UTF-8"?>
 <FeatureSet xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:noNamespaceSchemaLocation="FeatureSet-1.0.0.xsd">
    <Layer id="6e0efb1c-d07d-11df-8000-001276243361">
        <Class id="OGRSchema:edifici~edifici_tematizzati_view">
            <ID>OAAAAA==</ID>
        </Class>
    </Layer>
 </FeatureSet>

 2. SetSelectionXML(xmlSet) => setselection.php ----> 'xmlOut'

 <?xml version="1.0" encoding="UTF-8"?>
 <FeatureInformation>
    <FeatureSet xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:noNamespaceSchemaLocation="FeatureSet-1.0.0.xsd">
        <Layer id="6e0efb1c-d07d-11df-8000-001276243361">
            <Class id="OGRSchema:edifici~edifici_tematizzati_view">
                <ID>OAAAAA==</ID>
            </Class>
        </Layer>
    </FeatureSet>
   <Tooltip>tooltip</Tooltip>
   <Hyperlink>URL</Hyperlink>
   <Property name="id" value="56" />
   <Property name="anotherProperty" value="42" />
 </FeatureInformation>

 This 'xmlOut' contains all the properties of the feature and it is
 strangely discarded by ProcessFeatureInfo(xmlOut, false, 2)

 3. ProcessFeatureInfo(xmlOut, false, 2) calls
 RequestSelectedFeatureProperties() => getselectedfeature.php ---->
 resp

 {"edifici" : [{"values" : [{"name" : "id", "value" : "48" },{"name" :
 "anotherProperty", "value" : "42" }], "zoom" : { "x": 1673376.1291158,
 "y": 4736296.95092 } }]}

 Apart from the zoom (that IMHO is not used in further processing) this
 is simply the json version of the properties in xmlOut

 The whole selection can be
 obtained with only a call to a PHP script, that produces both 'xmlSet'
 and 'xmlOut', and its jsonified version 'resp' that can be passed to
 the ProcessSelectedFeatureSet(resp).
 Much less calls to the API and only one PHP pages called.

-- 
Ticket URL: <http://trac.osgeo.org/mapguide/ticket/1464>
MapGuide Open Source <http://mapguide.osgeo.org/>
MapGuide Open Source Internals