added custom column type JsonEncoder

ordr/models/meta.py

@@ -1,5 +1,10 @@
+''' SQL conventions and custom Encoders '''
+
+import json
+
 from sqlalchemy.ext.declarative import declarative_base
 from sqlalchemy.schema import MetaData
+from sqlalchemy.types import TypeDecorator, Unicode
 
 # Recommended naming convention used by Alembic, as various different database
 # providers will autogenerate vastly different names making migrations more
@@ -14,3 +19,21 @@ NAMING_CONVENTION = {
 
 metadata = MetaData(naming_convention=NAMING_CONVENTION)
 Base = declarative_base(metadata=metadata)
+
+
+class JsonEncoder(TypeDecorator):
+    ''' Custom type for storing data structures as json-encoded string. '''
+
+    impl = Unicode
+
+    def process_bind_param(self, value, dialect):
+        ''' inbound (to database) '''
+        if value is not None:
+            value = json.dumps(value)
+        return value
+
+    def process_result_value(self, value, dialect):
+        ''' outbound (from database) '''
+        if value is not None:
+            value = json.loads(value)
+        return value

ordr/tests/models/meta.py

@@ -0,0 +1,35 @@
+import pytest
+
+
+@pytest.mark.parametrize(
+    'value,expected', [
+        (None, None),
+        ([1, 2, 3], '[1, 2, 3]'),
+        ({'a':1, 'b':2}, '{"a": 1, "b": 2}'),
+        ]
+    )
+def test_json_encoder_bind(value, expected):
+    from ordr.models.meta import JsonEncoder
+    encoder = JsonEncoder()
+    assert encoder.process_bind_param(value, None) == expected
+
+
+@pytest.mark.parametrize(
+    'value,expected', [
+        (None, None),
+        ('[1, 2, 3]', [1, 2, 3]),
+        ('{"a": 1, "b":2}', {'a':1, 'b':2}),
+        ]
+    )
+def test_json_encoder_result(value, expected):
+    from ordr.models.meta import JsonEncoder
+    encoder = JsonEncoder()
+    assert encoder.process_result_value(value, None) == expected
+
+
+@pytest.mark.parametrize('value', [None, [1, 2, 3], {'a':1, 'b':2}])
+def test_json_encoder_bind_and_result(value):
+    from ordr.models.meta import JsonEncoder
+    encoder = JsonEncoder()
+    result = encoder.process_bind_param(value, None)
+    assert encoder.process_result_value(result, None) == value