Add test for dj.U, change make_SQL DISTINCT usage.

Author: jverswijver

datajoint/expression.py

@@ -101,12 +101,13 @@ def where_clause(self):
         return '' if not self.restriction else ' WHERE(%s)' % ')AND('.join(
             str(s) for s in self.restriction)
 
-    def make_sql(self, fields=None):
+    def make_sql(self, fields=None, distinct=True):
         """
         Make the SQL SELECT statement.
         :param fields: used to explicitly set the select attributes
         """
-        return 'SELECT {fields} FROM {from_}{where}'.format(
+        return 'SELECT {distinct}{fields} FROM {from_}{where}'.format(
+            distinct="DISTINCT " if distinct else "",
             fields=self.heading.as_sql(fields or self.heading.names),
             from_=self.from_clause(), where=self.where_clause())
 
@@ -508,9 +509,11 @@ def cursor(self, offset=0, limit=None, order_by=None, as_dict=False):
         """
         if offset and limit is None:
             raise DataJointError('limit is required when offset is set')
-        sql = self.make_sql()
         if order_by is not None:
+            sql = self.make_sql(distinct=False)
             sql += ' ORDER BY ' + ', '.join(order_by)
+        else:
+            sql = self.make_sql()
         if limit is not None:
             sql += ' LIMIT %d' % limit + (' OFFSET %d' % offset if offset else "")
         logger.debug(sql)

tests/schema.py

@@ -439,3 +439,13 @@ class SessionDateA(dj.Lookup):
         ('mouse1', '2020-12-03'),
         ('mouse1', '2020-12-04')
     ]
+
+
+@schema
+class Stimulus(dj.Lookup):
+    definition = """
+    id: int
+    ---
+    contrast: int
+    brightness: int
+    """

tests/test_fetch.py

@@ -6,7 +6,7 @@
 import pandas
 import warnings
 from . import schema
-from .schema import Parent
+from .schema import Parent, Stimulus
 import datajoint as dj
 import os
 
@@ -296,3 +296,33 @@ def test_fetch_group_by(self):
         fetchedData = Parent().fetch('KEY', order_by='name')
         print(fetchedData)
         assert fetchedData == expectedData
+
+    def test_dj_U_DISTINCT(self):
+        # Test developed to see if removing DISTINCT from the select statement
+        # generation breakes the dj.U universal set imlementation
+
+        # Contents to be inserted
+        contents = [
+            (1,2,3),
+            (2,2,3),
+            (3,3,2),
+            (4,5,5)
+        ]
+        Stimulus.insert(contents)
+
+        # Query the whole table
+        testQuery = Stimulus()
+
+        # Use dj.U to create a list of unique contrast and brightness combinations
+        result = dj.U('contrast', 'brightness') & testQuery
+        expectedResult = [{'contrast': 2, 'brightness': 3},
+                          {'contrast': 3, 'brightness': 2},
+                          {'contrast': 5, 'brightness': 5}]
+
+        fechedResult = result.fetch(as_dict=True)
+
+        # Cleanup table
+        Stimulus.delete()
+        print(result.make_sql())
+        # Test to see if the repeated row was removed in the results
+        assert fechedResult == expectedResult