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GQL to CSV exporter for Google App Engine

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The App Engine admin panel will let you run GQL queries against your datastore, but it won't let you download the results as a CSV. So I wrote a [very] quick and [very] dirty handler that does, which also has the handy side effect that you can put your own access controls on it. That means you can give someone on your team read-only access to your datastore without also giving them access to the admin panel.

If you're using db instead of ndb,  I believe the main thing to change is ndb.gql() to GqlQuery().

 # Very quick and dirty example of how to provide unfettered read  
# access to your datastore with export to CSV. Be sure to add appropriate
# access controls and watch out for security risks (like XSS)
#
# Don't forget to:
# from google.appengine.ext import ndb
# from google.appengine.ext.ndb import metadata
class GqlPage(webapp2.RequestHandler):
def get(self):
limited = True
row_limit = 1000
# Tricky to distinguish absence of 'limit' checkbox when you
# first hit the URL from when you submitted with an unchecked box
if self.request.get('download', 'nope') != 'nope' and \
self.request.get("limit", "nope") == "nope":
limited = False

query = self.request.get('query', "empty")

is_csv = False
if self.request.get('download') == 'Download':
is_csv = True
self.response.headers['Content-Type'] = "text/csv"
else:
self.response.write('<html><body>')
self.response.write('<form action="/gql" method=POST>')
self.response.write('<textarea name=query rows=10 cols=80 placeholder="select * from...">')
if query != "empty":
self.response.write(cgi.escape(query))
self.response.write('</textarea><br>')
self.response.write("<input type=submit name=download value=View>")
self.response.write('<input id=foo type=submit name=download value=Download')
self.response.write(' onclick="document.getElementById(\'results_div\').innerHTML=\'\';">')

self.response.write("Limit response to " + str(row_limit) + " rows:")
self.response.write("<input name=limit type=checkbox ")
if limited:
self.response.write("checked")
self.response.write('><br></form>')

self.response.write("Examples for available tables:<br>")
for kind in metadata.get_kinds():
self.response.write("select * from " + kind + "<br>")

self.response.write('<br><div id="results_div"><pre>')

if query != 'empty' and query != '':
results = []
if limited:
results = ndb.gql(query).fetch(row_limit)
else:
results = ndb.gql(query).fetch()

writer = csv.writer(self.response.out)

row_count = 0
first_row = True
for row in results:
row_dict = row.to_dict()
keys = sorted(row_dict.keys())

# Write column labels as first row
if first_row:
first_row = False
self.response.write("#")
writer.writerow(keys)

values = []
for k in keys:
value = str(row_dict[k])
if is_csv:
values.append(value)
else:
values.append(cgi.escape(value))

writer.writerow(values)

row_count += 1
if not is_csv and limited and row_count == row_limit:
self.response.write("\n[Truncated at " + str(row_limit) + " lines]")

if not is_csv:
self.response.write('</pre></div>')
self.response.write("</body></html>")

def post(self):
return self.get()


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