Change the parsing logic for constraint expressions

The original way we used pyparsing didn't make proper use of its features. This rewrites all constraint parsing to make use of setParseAction and uses infixNotation to handle the nested expressions. It should be a transparent change that has no effect of functionality.

dql/engine.py

@@ -444,8 +444,8 @@ def _build_query(self, table, tree, visitor):
         if tree.using:
             index_name = kwargs["index"] = tree.using[1]
             index = table.get_index(index_name)
-        if tree.where:
-            constraints = ConstraintExpression.from_where(tree.where)
+        if isinstance(tree.where, ConstraintExpression):
+            constraints = tree.where
             possible_hash = constraints.possible_hash_fields()
             possible_range = constraints.possible_range_fields()
             if index is None:
@@ -705,9 +705,8 @@ def _delete(self, tree):
         table = self.describe(tablename, require=True)
         kwargs = {}
         visitor = Visitor(self.reserved_words)
-        if tree.where:
-            constraints = ConstraintExpression.from_where(tree.where)
-            kwargs["condition"] = constraints.build(visitor)
+        if isinstance(tree.where, ConstraintExpression):
+            kwargs["condition"] = tree.where.build(visitor)
         kwargs["expr_values"] = visitor.expression_values
         kwargs["alias"] = visitor.attribute_names
         return self._query_and_op(tree, table, "delete_item", kwargs)
@@ -726,9 +725,8 @@ def _update(self, tree):
         visitor = Visitor(self.reserved_words)
         updates = UpdateExpression.from_update(tree.update)
         kwargs["expression"] = updates.build(visitor)
-        if tree.where:
-            constraints = ConstraintExpression.from_where(tree.where)
-            kwargs["condition"] = constraints.build(visitor)
+        if isinstance(tree.where, ConstraintExpression):
+            kwargs["condition"] = tree.where.build(visitor)
         kwargs["expr_values"] = visitor.expression_values
         kwargs["alias"] = visitor.attribute_names
         return self._query_and_op(tree, table, "update_item", kwargs)

dql/expressions/base.py

@@ -47,6 +47,12 @@ def evaluate(self, item):
             return None
         return item
 
+    def __hash__(self):
+        return hash(self.field)
+
+    def __eq__(self, other):
+        return isinstance(other, Field) and self.field == other.field
+
 
 class Value(Expression):
 
@@ -61,3 +67,9 @@ def build(self, visitor):
     def evaluate(self, item):
         """ Values evaluate to themselves regardless of the item """
         return self.value
+
+    def __hash__(self):
+        return hash(self.value)
+
+    def __eq__(self, other):
+        return isinstance(other, Value) and self.value == other.value