Properly handle non-nullable relationships (#645)

* Properly handle non-nullable relationships

* Add test case for nullable foreign key

CHANGELOG.rst

@@ -15,6 +15,9 @@ Bug fixes:
 * Fix behavior of ``include_fk = False`` in options when parent
   schema sets ``include_fk = True`` (:issue:`440`).
   Thanks :user:`uhnomoli` for reporting.
+* Fields generated from non-nullable `sqlalchemy.orm.relationship`
+  correctly set ``required=True`` and ``allow_none=False`` (:issue:`336`).
+  Thanks :user:`AbdealiLoKo` for reporting.
 
 Other changes:
 

src/marshmallow_sqlalchemy/convert.py

@@ -458,7 +458,10 @@ def _add_relationship_kwargs(
         nullable = True
         for pair in prop.local_remote_pairs:
             if not pair[0].nullable:
-                if prop.uselist is True:
+                if (
+                    prop.uselist is True
+                    or self.DIRECTION_MAPPING[prop.direction.name] is False
+                ):
                     nullable = False
                 break
         kwargs.update({"allow_none": nullable, "required": not nullable})

tests/test_conversion.py

@@ -86,18 +86,36 @@ def test_enum_with_class_converted_to_enum_field(self, models):
 
     def test_many_to_many_relationship(self, models):
         student_fields = fields_for_model(models.Student, include_relationships=True)
-        assert type(student_fields["courses"]) is RelatedList
+        courses_field = student_fields["courses"]
+        assert type(courses_field) is RelatedList
+        assert courses_field.required is False
 
         course_fields = fields_for_model(models.Course, include_relationships=True)
-        assert type(course_fields["students"]) is RelatedList
+        students_field = course_fields["students"]
+        assert type(students_field) is RelatedList
+        assert students_field.required is False
 
     def test_many_to_one_relationship(self, models):
         student_fields = fields_for_model(models.Student, include_relationships=True)
-        assert type(student_fields["current_school"]) is Related
+        current_school_field = student_fields["current_school"]
+        assert type(current_school_field) is Related
+        assert current_school_field.allow_none is False
+        assert current_school_field.required is True
 
         school_fields = fields_for_model(models.School, include_relationships=True)
         assert type(school_fields["students"]) is RelatedList
 
+        teacher_fields = fields_for_model(models.Teacher, include_relationships=True)
+        current_school_field = teacher_fields["current_school"]
+        assert type(current_school_field) is Related
+        assert current_school_field.required is False
+
+    def test_many_to_many_uselist_false_relationship(self, models):
+        teacher_fields = fields_for_model(models.Teacher, include_relationships=True)
+        substitute_field = teacher_fields["substitute"]
+        assert type(substitute_field) is Related
+        assert substitute_field.required is False
+
     def test_include_fk(self, models):
         student_fields = fields_for_model(models.Student, include_fk=False)
         assert "current_school_id" not in student_fields