Some convenience methods

relational/optimizations.py

@@ -223,8 +223,8 @@ def swap_union_renames(n: parser.Node) -> Tuple[parser.Node, int]:
     ρ a➡b(R ∪ Q).
     Does the same with subtraction and intersection'''
     if n.name in (DIFFERENCE, UNION, INTERSECTION) and n.left.name == RENAME and n.right.name == RENAME:
-        l_vars = n.left.rename_dict()
-        r_vars = n.right.rename_dict()
+        l_vars = n.left.get_rename_prop()
+        r_vars = n.right.get_rename_prop()
         if r_vars == l_vars:
             child = parser.Binary(n.name, n.left.child, n.right.child)
             return parser.Unary(RENAME, n.left.prop, child), 1
@@ -240,7 +240,7 @@ def futile_renames(n: parser.Node) -> Tuple[parser.Node, int]:
     or removes the operation entirely if they all get removed
     '''
     if n.name == RENAME:
-        renames = n.rename_dict()
+        renames = n.get_rename_prop()
         changes = False
         for k, v in renames.items():
             if k == v:
@@ -250,7 +250,7 @@ def futile_renames(n: parser.Node) -> Tuple[parser.Node, int]:
             return n.child, 1
         elif changes:
             # Changing the node in place, no need to return to cause a recursive step
-            n.prop = ','.join(f'{k}{ARROW}{v}' for k, v in renames.items())
+            n.set_rename_prop(renames)
 
     return n, 0
 
@@ -286,8 +286,8 @@ def subsequent_renames(n: parser.Node) -> Tuple[parser.Node, int]:
 
         if len(renames) == 0:  # Nothing to rename, removing the rename op
             return n, 1
-        elif changes:
-            n.prop = ','.join(f'{k}{ARROW}{v}' for k, v in renames.items())
+        else:
+            n.set_rename_prop(renames)
             return n, 1
 
     return n, 0

relational/parser.py

@@ -233,13 +233,23 @@ class Unary(Node):
         if self.name == PROJECTION:
             prop = '\"%s\"' % prop.replace(' ', '').replace(',', '\",\"')
         elif self.name == RENAME:
-            prop = repr(self.rename_dict())
+            prop = repr(self.get_rename_prop())
         else:  # Selection
             prop = repr(prop)
 
         return '%s.%s(%s)' % (self.child._toPython(), op_functions[self.name], prop)
 
-    def rename_dict(self) -> Dict[str, str]:
+    def get_projection_prop(self) -> List[str]:
+        if self.name != PROJECTION:
+            raise ValueError('This is only supported on projection nodes')
+        return [i.strip() for i in self.prop.split(',')]
+
+    def set_projection_prop(self, p: List[str]) -> None:
+        if self.name != PROJECTION:
+            raise ValueError('This is only supported on projection nodes')
+        self.prop = ','.join(p)
+
+    def get_rename_prop(self) -> Dict[str, str]:
         '''
         Returns the dictionary that the rename operation wants
         '''
@@ -251,6 +261,15 @@ class Unary(Node):
             r[q[0].strip()] = q[1].strip()
         return r
 
+    def set_rename_prop(self, renames: Dict[str, str]) -> None:
+        '''
+        Sets the prop field based on the dictionary for renames
+        '''
+        if self.name != RENAME:
+            raise ValueError('This is only supported on rename nodes')
+        self.prop = ','.join(f'{k}{ARROW}{v}' for k, v in renames.items())
+
+
 
 
 def parse_tokens(expression: List[Union[list, str]]) -> Node: