Add getdotattr

sqlalchemy_utils/functions/__init__.py

@@ -12,37 +12,39 @@ from .database import (
     non_indexed_foreign_keys,
 )
 from .orm import (
-    primary_keys,
-    table_name,
     declarative_base,
+    getdotattr,
     has_changes,
     identity,
     naturally_equivalent,
-    remove_property
+    primary_keys,
+    remove_property,
+    table_name,
 )
 
 __all__ = (
-    create_mock_engine,
-    defer_except,
-    mock_engine,
-    sort_query,
-    render_expression,
-    render_statement,
-    QuerySorterException,
-    database_exists,
     create_database,
+    create_mock_engine,
+    database_exists,
+    declarative_base,
+    defer_except,
     drop_database,
     escape_like,
-    is_auto_assigned_date_column,
+    getdotattr,
-    is_indexed_foreign_key,
-    non_indexed_foreign_keys,
-    remove_property,
-    primary_keys,
-    table_name,
-    declarative_base,
     has_changes,
     identity,
+    is_auto_assigned_date_column,
+    is_indexed_foreign_key,
+    mock_engine,
     naturally_equivalent,
+    non_indexed_foreign_keys,
+    primary_keys,
+    QuerySorterException,
+    remove_property,
+    render_expression,
+    render_statement,
+    sort_query,
+    table_name,
 )
 
 

sqlalchemy_utils/functions/orm.py

@@ -1,7 +1,9 @@
 from functools import partial
 from toolz import curry, first
+import six
 import sqlalchemy as sa
 from sqlalchemy import inspect
+from sqlalchemy.orm.attributes import InstrumentedAttribute
 from sqlalchemy.orm.query import _ColumnEntity
 from sqlalchemy.orm.mapper import Mapper
 from sqlalchemy.orm.util import AliasedInsp
@@ -218,6 +220,32 @@ def declarative_base(model):
     return model
 
 
+def getdotattr(obj_or_class, dot_path):
+    """
+    Allow dot-notated strings to be passed to `getattr`.
+
+    ::
+
+        getdotattr(SubSection, 'section.document')
+
+        getdotattr(subsection, 'section.document')
+
+
+    :param obj_or_class: Any object or class
+    :param dot_path: Attribute path with dot mark as separator
+    """
+    def get_attr(mixed, attr):
+        if isinstance(mixed, InstrumentedAttribute):
+            return getattr(
+                mixed.property.mapper.class_,
+                attr
+            )
+        else:
+            return getattr(mixed, attr)
+
+    return six.moves.reduce(get_attr, dot_path.split('.'), obj_or_class)
+
+
 def has_changes(obj, attr):
     """
     Simple shortcut function for checking if given attribute of given

tests/functions/test_getdotattr.py

@@ -0,0 +1,59 @@
+import sqlalchemy as sa
+from sqlalchemy_utils.functions import getdotattr
+from tests import TestCase
+
+
+
+class TestTwoWayAttributeValueGeneration(TestCase):
+    def create_models(self):
+        class Document(self.Base):
+            __tablename__ = 'document'
+            id = sa.Column(sa.Integer, primary_key=True)
+            name = sa.Column(sa.Unicode(255))
+            locale = sa.Column(sa.String(10))
+
+        class Section(self.Base):
+            __tablename__ = 'section'
+            id = sa.Column(sa.Integer, primary_key=True)
+            name = sa.Column(sa.Unicode(255))
+            locale = sa.Column(sa.String(10))
+
+            document_id = sa.Column(
+                sa.Integer, sa.ForeignKey(Document.id)
+            )
+
+            document = sa.orm.relationship(Document)
+
+        class SubSection(self.Base):
+            __tablename__ = 'subsection'
+            id = sa.Column(sa.Integer, primary_key=True)
+            name = sa.Column(sa.Unicode(255))
+            locale = sa.Column(sa.String(10))
+
+            section_id = sa.Column(
+                sa.Integer, sa.ForeignKey(Section.id)
+            )
+
+            section = sa.orm.relationship(Section)
+
+        self.Document = Document
+        self.Section = Section
+        self.SubSection = SubSection
+
+    def test_getdotattr_for_objects(self):
+        document = self.Document(name=u'some document')
+        section = self.Section(document=document)
+        subsection = self.SubSection(section=section)
+
+        assert getdotattr(
+            subsection,
+            'section.document.name'
+        ) == u'some document'
+
+    def test_getdotattr_for_class_paths(self):
+        assert getdotattr(self.Section, 'document') is self.Section.document
+        assert (
+            getdotattr(self.SubSection, 'section.document') is
+            self.Section.document
+        )
+        assert getdotattr(self.Section, 'document.name') is self.Document.name