Idiomatic & easy to read way of defining events

.gitignore

@@ -1,5 +1,8 @@
 .tox
+.coverage
+.cache
 venv
+cq.egg-info
 *.pyc
 *.log
 *.bak

cq/events.py

@@ -1,13 +1,54 @@
-import datetime
+import uuid
+from .genuuid import genuuid
+from datetime import datetime
+from pyrsistent import field
+from pyrsistent import PRecord
+from pyrsistent import InvariantException
 
 
-class Event:
-    def __init__(self, id, name, aggregate_id, data=None, ts=None):
-        self.id = id
-        self.name = name
-        self.aggregate_id = aggregate_id
-        self.data = data
-        self.ts = ts or datetime.datetime.now()
+def isoformat(format, dt):
+    return dt.isoformat()
 
-    def __str__(self):
-        return '%s | %s | %s' % (self.name, self.aggregate_id, self.ts)
+
+def get_datetime(val=None):
+    if not val:
+        return datetime.utcnow()
+    return val
+
+
+def get_id():
+    return genuuid()
+
+
+class EventBody(PRecord):
+    """
+    Base class for `Event.data` field definition.
+    Note: I would suggest `Event` name instead.
+    """
+    pass
+
+
+class Event(PRecord):
+    """
+    Base event class that specifies must have event fields.
+    Note: I would suggest `EventEnvelope` name instead.
+    """
+    # pyrsistent style event class, like the simplicity of the syntax
+    # UUID & date validation could be added easily.
+    # Serialization is pretty much out of the box here as well.
+    id = field(mandatory=True, type=str, initial=get_id)
+    aggregate_id = field(mandatory=True, type=str)
+    name = field(mandatory=True, type=str)
+    ts = field(
+        mandatory=True,
+        type=datetime,
+        # use `get_datetime` is ts is not provided on init
+        initial=get_datetime,
+        # use `get_datetime` if `ts=None` on init
+        factory=get_datetime,
+        serializer=isoformat
+    )
+
+    # type below should be PRecord or None.
+    # `dict` is left for now, to allieviate fixing alll the failing tests
+    data = field(type=(EventBody, dict, type(None)))

cq/tests/test_events.py

@@ -0,0 +1,79 @@
+from ..storages import LocalMemoryStorage
+from ..storages import Storage
+from cq import events
+from datetime import datetime
+from freezegun import freeze_time
+from unittest import mock
+import pytest
+
+
+# Base `Event` class tests.
+
+def test_assigns_all_properties():
+    d = datetime.utcnow()
+    e = events.Event(id='evt', aggregate_id='agg', ts=d, name='evt_name', data=None)
+
+    assert e.id == 'evt'
+    assert e.aggregate_id == 'agg'
+    assert e.ts == d
+    assert e.name == 'evt_name'
+
+
+def test_requires_needed_properties():
+    with pytest.raises(events.InvariantException) as exc:
+        e = events.Event()
+
+
+@freeze_time('2000-1-1')
+@mock.patch.object(events, 'genuuid', return_value='evt_uuid')
+def test_default_values_fields(_):
+    e = events.Event(aggregate_id='agg', name='evt_name')
+
+    assert e.id == 'evt_uuid'
+    assert e.aggregate_id == 'agg'
+    assert e.ts == datetime(2000, 1, 1)
+    assert e.name == 'evt_name'
+
+
+@freeze_time('2000-1-1')
+@mock.patch.object(events, 'genuuid', return_value='evt_uuid')
+def test_base_serialization(_):
+    d = datetime.utcnow()
+    e = events.Event(id='evt', aggregate_id='agg', ts=d, name='evt_name', data=None)
+
+    assert e.serialize() == {
+        'id': 'evt',
+        'aggregate_id': 'agg',
+        'data': None,
+        'name': 'evt_name',
+        'ts': '2000-01-01T00:00:00'
+    }
+
+
+# More complex tests against event data nesting & serialization
+
+class UserCreatedEvent(events.EventBody):
+    """
+    Sample event body class for User.Created event.
+    """
+    name = events.field(mandatory=True, type=str)
+    email = events.field(mandatory=True, type=str)
+    age = events.field(type=int)
+
+
+@freeze_time('2000-1-1')
+def test_complex_serialization():
+    data = UserCreatedEvent(name='John', email='[email protected]', age=20)
+    e = events.Event(id='evt', aggregate_id='agg', name='evt_name', data=data)
+
+    assert e.serialize() == {
+        'id': 'evt',
+        'aggregate_id': 'agg',
+        'name': 'evt_name',
+        'ts': '2000-01-01T00:00:00',
+        'data': {
+            'name': 'John',
+            'email': '[email protected]',
+            'age': 20
+        }
+    }

cq/tests/test_storages.py

@@ -1,5 +1,8 @@
+from ..genuuid import genuuid
 from ..storages import LocalMemoryStorage
 from ..storages import Storage
+from datetime import datetime
+from pyrsistent import PRecord, field
 from unittest import mock
 import pytest
 
@@ -28,21 +31,25 @@ def test_store(publish):
 
 
 def test_local__append(local_storage):
-    local_storage.store('User.Registered', 'JOE_ID', {'name': 'joe'}, 'TS')
-    local_storage.store('User.Registered', 'JANE_ID', {'name': 'jane'}, 'TS')
-    local_storage.store('User.Activated', 'JOE_ID', ts='TS')
+    ts = datetime.utcnow()
+
+    local_storage.store('User.Registered', 'JOE_ID', {'name': 'joe'}, ts)
+    local_storage.store('User.Registered', 'JANE_ID', {'name': 'jane'}, ts)
+    local_storage.store('User.Activated', 'JOE_ID', ts=ts)
 
     assert [(e.name, e.aggregate_id, e.data, e.ts) for e in local_storage.events] == [
-        ('User.Registered', 'JOE_ID', {'name': 'joe'}, 'TS'),
-        ('User.Registered', 'JANE_ID', {'name': 'jane'}, 'TS'),
-        ('User.Activated', 'JOE_ID', None, 'TS'),
+        ('User.Registered', 'JOE_ID', {'name': 'joe'}, ts),
+        ('User.Registered', 'JANE_ID', {'name': 'jane'}, ts),
+        ('User.Activated', 'JOE_ID', None, ts),
     ]
 
 
 def test_local__get_events(local_storage):
-    local_storage.store('User.Registered', 'JOE_ID', {'name': 'joe'}, 'TS')
-    local_storage.store('User.Registered', 'JANE_ID', {'name': 'jane'}, 'TS')
-    local_storage.store('User.Activated', 'JOE_ID', {'name': 'joe'}, 'TS')
+    ts = datetime.utcnow()
+
+    local_storage.store('User.Registered', 'JOE_ID', {'name': 'joe'}, ts)
+    local_storage.store('User.Registered', 'JANE_ID', {'name': 'jane'}, ts)
+    local_storage.store('User.Activated', 'JOE_ID', {'name': 'joe'}, ts)
 
     assert [(e.name, e.aggregate_id) for e in local_storage.get_events('JOE_ID')] == [
         ('User.Registered', 'JOE_ID'),

setup.py

@@ -25,6 +25,7 @@ def get_packages(top):
     packages=get_packages('cq'),
     include_package_data=True,
     install_requires=[
+        'pyrsistent',
         'jsonfield',  # TODO: only needed django, make it optional
     ],
 )