[#1776] Fix bug when upserting [] on JSON column in the datastore

We were testing that the new value wasn't `None` using `if value`. As `[]` is a
falsy value, we never went through that `if` and ended up trying to run an
invalid SQL query.

This commit fixes that by explictly testing `if value is not None`.

This was first discovered in
http://stackoverflow.com/questions/24207065/inserting-empty-arrays-in-json-type-fields-in-datastore

ckanext/datastore/db.py

@@ -620,7 +620,7 @@ def upsert_data(context, data_dict):
 
             for field in fields:
                 value = record.get(field['id'])
-                if value and field['type'].lower() == 'nested':
+                if value is not None and field['type'].lower() == 'nested':
                     ## a tuple with an empty second value
                     record[field['id']] = (json.dumps(value), '')
 

ckanext/datastore/tests/test_upsert.py

@@ -13,6 +13,8 @@
 import ckanext.datastore.db as db
 from ckanext.datastore.tests.helpers import rebuild_all_dbs
 
+assert_equal = nose.tools.assert_equal
+
 
 class TestDatastoreUpsert(tests.WsgiAppCase):
     sysadmin_user = None
@@ -236,6 +238,33 @@ def test_upsert_non_existing_field(self):
 
         assert res_dict['success'] is False
 
+    def test_upsert_works_with_empty_list_in_json_field(self):
+        hhguide = u"hitchhiker's guide to the galaxy"
+
+        data = {
+            'resource_id': self.data['resource_id'],
+            'method': 'upsert',
+            'records': [{
+                'nested': [],
+                u'b\xfck': hhguide}]
+        }
+
+        postparams = '%s=1' % json.dumps(data)
+        auth = {'Authorization': str(self.sysadmin_user.apikey)}
+        res = self.app.post('/api/action/datastore_upsert', params=postparams,
+                            extra_environ=auth)
+        res_dict = json.loads(res.body)
+        assert res_dict['success'] is True, res_dict
+
+        c = self.Session.connection()
+        results = c.execute('select * from "{0}"'.format(data['resource_id']))
+        record = [r for r in results.fetchall() if r[2] == hhguide]
+        self.Session.remove()
+        assert len(record) == 1, record
+        assert_equal(json.loads(record[0][4].json),
+                     data['records'][0]['nested'])
+
+
 
 class TestDatastoreInsert(tests.WsgiAppCase):
     sysadmin_user = None