fix for "ValueError: 'column_name' is not in list" error on sync_table for models with primary keys only

https://github.com/cqlengine/cqlengine/issues/175

cqlengine/management.py

@@ -65,6 +65,16 @@ def create_table(model, create_missing_keyspace=True):
     sync_table(model, create_missing_keyspace)
 
 def sync_table(model, create_missing_keyspace=True):
+    """
+    Inspects the model and creates / updates the corresponding table and columns.
+
+    Note that the attributes removed from the model are not deleted on the database.
+    They become effectively ignored by (will not show up on) the model.
+
+    :param create_missing_keyspace: (Defaults to True) Flags to us that we need to create missing keyspace
+        mentioned in the model automatically.
+    :type create_missing_keyspace: bool
+    """
 
     if model.__abstract__:
         raise CQLEngineException("cannot create table from abstract model")
@@ -238,12 +248,19 @@ def get_fields(model):
 
         tmp = con.execute(query, {'ks_name': ks_name, 'col_family': col_family}, ONE)
 
-    column_indices = [tmp.columns.index('column_name'), tmp.columns.index('validator')]
+    # Tables containing only primary keys do not appear to create
+    # any entries in system.schema_columns, as only non-primary-key attributes
+    # appear to be inserted into the schema_columns table
+    if not tmp.results:
+        return []
+
+    column_name_positon = tmp.columns.index('column_name')
+    validator_positon = tmp.columns.index('validator')
     try:
-        type_index = tmp.columns.index('type')
+        type_position = tmp.columns.index('type')
-        return [Field(x[column_indices[0]], x[column_indices[1]]) for x in tmp.results if x[type_index] == 'regular']
+        return [Field(x[column_name_positon], x[validator_positon]) for x in tmp.results if x[type_position] == 'regular']
     except ValueError:
-        return [Field(x[column_indices[0]], x[column_indices[1]]) for x in tmp.results]
+        return [Field(x[column_name_positon], x[validator_positon]) for x in tmp.results]
     # convert to Field named tuples
 
 

cqlengine/tests/management/test_management.py

@@ -2,7 +2,7 @@ from mock import MagicMock, patch
 
 from cqlengine import ONE
 from cqlengine.exceptions import CQLEngineException
-from cqlengine.management import create_table, delete_table, get_fields
+from cqlengine.management import create_table, delete_table, get_fields, sync_table
 from cqlengine.tests.base import BaseCassEngTestCase
 from cqlengine.connection import ConnectionPool, Host
 from cqlengine import management
@@ -77,6 +77,11 @@ class CapitalizedKeyModel(Model):
     secondKey = columns.Integer(primary_key=True)
     someData = columns.Text()
 
+class PrimaryKeysOnlyModel(Model):
+    first_ey = columns.Integer(primary_key=True)
+    second_key = columns.Integer(primary_key=True)
+
+
 class CapitalizedKeyTest(BaseCassEngTestCase):
 
     def test_table_definition(self):
@@ -142,3 +147,17 @@ class AddColumnTest(BaseCassEngTestCase):
         self.assertEqual(len(fields), 4)
 
 
+class SyncTableTests(BaseCassEngTestCase):
+
+    def setUp(self):
+        delete_table(PrimaryKeysOnlyModel)
+
+    def test_sync_table_works_with_primary_keys_only_tables(self):
+        sync_table(PrimaryKeysOnlyModel)
+
+        # primary-keys-only tables do not create entries in system.schema_columns
+        # table. Only non-primary keys are added to that table.
+        # Our code must deal with that eventuality properly (not crash)
+        # on subsequent runs of sync_table (which runs get_fields internally)
+        get_fields(PrimaryKeysOnlyModel)
+        sync_table(PrimaryKeysOnlyModel)