Thursday, February 21, 2013

Query Feature Service By Object IDs (Python)

To query a feature service using object ids, you need to perform a POST.  For those who don't know the difference between a "GET" and "POST" here is a quick blurb based on the HTML specifications:
"POST" means that former means that form data is to be encoded (by a browser) into a URL while the "GET" means that the form data is to appear within a message body. 

Even simpler, "GET" is basically for just getting data where a "POST" may involve anything, like updating data, sending, or creating data.

Using python, you can perform both "GET" and "POST" methods, but since we need a "POST" to query by IDs, here is a simple example.  Please note that most feature services limit 1000 features being returned, so if you want to grab all of the features from a feature service, you'll have to perform multiple queries to get all the features back in JSON format.


import urllib2
import urllib
import urlparse
import httplib

def query_by_objectid(url, objectIDStart=0, objectIDEnd=1001):
    """ performs a POST operation where the query is called using
        the object id method.  If a feature service has more than
        1000 records, use this method to get a range of features
        from the feature service.

           :url:  - string of feature service URL
           :objectIDStart: - integer of the start whole number
           :objectIDEnd: - end range whole number
           returns string JSON of query
    url = url + '/query'
    start = int(objectIDStart)
    end = int(objectIDEnd)

    objectIDs = ",".join([str(x) for x in range(start, end)])
    headers = {"Content-type": "application/x-www-form-urlencoded",
               "Accept": "text/plain"}
    parameters = {'objectIds' : objectIDs,
                  'f' : 'json'}
    urlparams = urllib.urlencode(parameters)
    parts = urlparse.urlparse(url)
    h = httplib.HTTPConnection(parts.netloc)
    headers = {"Content-type": "application/x-www-form-urlencoded", "Accept": "text/plain"}
    h.request('POST', parts.path, urlparams, headers)
    r = h.getresponse()

if __name__ == "__main__":
    url = ''
    print query_by_objectid(url=url,

So we have a simple "POST" example. This sample should work with both ArcGIS Server 10.1 and ArcGIS Online feature services.

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