added target attribute value sanity check for `db to aleph`

workflows/mysql/converters.py

@@ -170,6 +170,10 @@ class Aleph_Converter(ILP_Converter):
                     pos_rows.append(row)
                 else:
                     neg_rows.append(row)
+
+            if not pos_rows:
+                raise Exception('No positive examples with the given target attribute value, please re-check.')
+
             self.__pos_examples = '\n'.join(['%s(%s).' % (self.__target_predicate(), id) for _, id in pos_rows])
             self.__neg_examples = '\n'.join(['%s(%s).' % (self.__target_predicate(), id) for _, id in neg_rows])
         return self.__pos_examples, self.__neg_examples

workflows/mysql/library.py

@@ -32,7 +32,10 @@ def mysql_rsd_converter(input_dict):
 
 def mysql_aleph_converter(input_dict):
     dump = input_dict['dump'] == 'true'
-    aleph = Aleph_Converter(input_dict['context'], target_att_val=input_dict['target_att_val'], discr_intervals=input_dict['discr_intervals'] or {}, dump=dump)
+    target_att_val = input_dict['target_att_val']
+    if not target_att_val:
+        raise Exception('Please specify a target attribute value.')
+    aleph = Aleph_Converter(input_dict['context'], target_att_val=target_att_val, discr_intervals=input_dict['discr_intervals'] or {}, dump=dump)
     return {'pos_examples' : aleph.positive_examples(), 'neg_examples' : aleph.negative_examples(), 'bk' : aleph.background_knowledge()}
 
 def mysql_treeliker_converter(input_dict):