Refacto: introduce intermediary methods to create cells in case of pr…

…imary key constraint and considering case-sensitivity

frictionless/resources/table.py

@@ -413,18 +413,29 @@ def primary_key_cells(
         self,
         row: Row,
         case_sensitive: bool
-    ) -> Tuple[Row, Any]:
+    ) -> Tuple[str, Any]:
         """Create a tuple containg all cells related to primary_key
         """
+        return tuple(row[label] for label in
+                     self.labels_related_to_primary_key(row, case_sensitive))
+
+    def labels_related_to_primary_key(
+        self,
+        row: Row,
+        case_sensitive: bool,
+    ) -> List[str]:
+        """Create a list of TabelResource labels which correspond to the
+        primary_key schema considering case-sensitivity
+        """
         if case_sensitive:
-            cells = tuple(row[name] for name in self.schema.primary_key)
-        else:  # Ignore case
-            lower_primary_keys = [
+            labels_primary_key = self.schema.primary_key
+        else:
+            lower_primary_key = [
                 pk.lower() for pk in self.schema.primary_key
             ]
-            labels_primary_key = [label for label in row.field_names if label.lower() in lower_primary_keys]
-            cells = tuple(row[label] for label in labels_primary_key)
-        return cells
+            labels_primary_key = [label for label in row.field_names
+                                  if label.lower() in lower_primary_key]
+        return labels_primary_key
 
     # Read
     def read_cells(self, *, size: Optional[int] = None) -> List[List[Any]]: