add optional undefined_as_null param in to_filter

pygeofilter/backends/sqlalchemy/evaluate.py

@@ -8,8 +8,9 @@
 
 
 class SQLAlchemyFilterEvaluator(Evaluator):
-    def __init__(self, field_mapping):
+    def __init__(self, field_mapping, undefined_as_null):
         self.field_mapping = field_mapping
+        self.undefined_as_null = undefined_as_null
 
     @handle(ast.Not)
     def not_(self, node, sub):
@@ -105,7 +106,7 @@ def bbox(self, node, lhs):
 
     @handle(ast.Attribute)
     def attribute(self, node):
-        return filters.attribute(node.name, self.field_mapping)
+        return filters.attribute(node.name, self.field_mapping, self.undefined_as_null)
 
     @handle(ast.Arithmetic, subclasses=True)
     def arithmetic(self, node, lhs, rhs):
@@ -133,15 +134,13 @@ def envelope(self, node):
         return filters.parse_bbox([node.x1, node.y1, node.x2, node.y2])
 
 
-def to_filter(ast, field_mapping=None):
-    """Helper function to translate ECQL AST to Django Query expressions.
+def to_filter(ast, field_mapping={}, undefined_as_null=None):
+    """Helper function to translate ECQL AST to SQLAlchemy Query expressions.
 
     :param ast: the abstract syntax tree
-    :param field_mapping: a dict mapping from the filter name to the Django
+    :param field_mapping: a dict mapping from the filter name to the SQLAlchemy
                           field lookup.
-    :param mapping_choices: a dict mapping field lookups to choices.
     :type ast: :class:`Node`
-    :returns: a Django query object
-    :rtype: :class:`django.db.models.Q`
+    :returns: a SQLAlchemy query object
     """
-    return SQLAlchemyFilterEvaluator(field_mapping).evaluate(ast)
+    return SQLAlchemyFilterEvaluator(field_mapping, undefined_as_null).evaluate(ast)

pygeofilter/backends/sqlalchemy/filters.py

@@ -4,7 +4,7 @@
 from typing import Callable, Dict
 
 from pygeoif import shape
-from sqlalchemy import and_, func, not_, or_
+from sqlalchemy import and_, func, not_, or_, null
 
 def parse_bbox(box, srid: int = None):
     minx, miny, maxx, maxy = box
@@ -256,15 +256,21 @@ def bbox(lhs, minx, miny, maxx, maxy, crs=4326):
     return lhs.ST_Intersects(parse_bbox([minx, miny, maxx, maxy], crs))
 
 
-def attribute(name, field_mapping=None):
+def attribute(name, field_mapping={}, undefined_as_null: bool = None):
     """Create an attribute lookup expression using a field mapping dictionary.
 
     :param name: the field filter name
     :param field_mapping: the dictionary to use as a lookup.
+    :param undefined_as_null: how to handle a name not present in field_mapping
+        (None (default) - leave as-is; True - treat as null; False - throw error)
     """
-    field = field_mapping.get(name, name)
-
-    return field
+    if undefined_as_null is None:
+        return field_mapping.get(name, name)
+    if undefined_as_null:
+        # return null object if name is not found in field_mapping
+        return field_mapping.get(name, null())
+    # undefined_as_null is False, so raise KeyError if name not found
+    return field_mapping[name]
 
 
 def literal(value):

tests/backends/sqlalchemy/test_evaluate.py

@@ -152,9 +152,9 @@ def db_session(setup_database, connection):
     transaction.rollback()
 
 
-def evaluate(session, cql_expr, expected_ids):
+def evaluate(session, cql_expr, expected_ids, filter_option=None):
     ast = parse(cql_expr)
-    filters = to_filter(ast, FIELD_MAPPING)
+    filters = to_filter(ast, FIELD_MAPPING, filter_option)
 
     q = session.query(Record).join(RecordMeta).filter(filters)
     results = [row.identifier for row in q]
@@ -415,3 +415,21 @@ def test_arith_field_plus_mul_1(db_session):
 
 def test_arith_field_plus_mul_2(db_session):
     evaluate(db_session, "intMetaAttribute = 5 + intAttribute * 1.5", ("A",))
+
+
+# handling undefined/invalid attributes
+
+
+def test_undef_comp(db_session):
+    # treat undefined/invalid attribute as null
+    evaluate(db_session, "missingAttribute > 10", (), True)
+
+
+def test_undef_isnull(db_session):
+    evaluate(db_session, "missingAttribute IS NULL", ("A", "B"), True)
+
+
+def test_undef_comp_error(db_session):
+    # error if undefined/invalid attribute
+    with pytest.raises(KeyError):
+        evaluate(db_session, "missingAttribute > 10", (), False)