Adjusted 'cb' properties in "slices".

Author: johnbywater

eventsourcing/dcb/domain.py

@@ -104,7 +104,36 @@ class MetaPerspective(type):
     pass
 
 
-class SupportsEventDecorator(MetaPerspective):
+class Perspective(metaclass=MetaPerspective):
+    def __new__(cls, *_: Any, **__: Any) -> Self:
+        perspective = super().__new__(cls)
+        perspective.__base_init__()
+        return perspective
+
+    def __base_init__(self) -> None:
+        self.last_known_position: int | None = None
+        self.new_decisions: list[Mutates] = []
+
+    def append(self, *new_decisions: Mutates) -> None:
+        self.new_decisions.extend(new_decisions)
+
+    def collect_events(self) -> Sequence[Mutates]:
+        collected, self.new_decisions = self.new_decisions, []
+        return collected
+
+    @property
+    def cb(self) -> Selector | Sequence[Selector]:
+        raise NotImplementedError  # pragma: no cover
+
+
+TPerspective = TypeVar("TPerspective", bound=Perspective)
+
+
+given_event_class_mapping: dict[type[Mutates], type[DecoratedFuncCaller]] = {}
+decorated_funcs: dict[tuple[MetaPerspective, type[Mutates]], CallableType] = {}
+
+
+class MetaSupportsEventDecorator(MetaPerspective):
     def __init__(
         cls, name: str, bases: tuple[type, ...], namespace: dict[str, Any]
     ) -> None:
@@ -198,36 +227,7 @@ def _insert_decorator_func_caller(
         return func_caller
 
 
-class Perspective(metaclass=MetaPerspective):
-    last_known_position: int | None
-    new_decisions: tuple[Mutates, ...]
-
-    def __new__(cls, *_: Any, **__: Any) -> Self:
-        perspective = super().__new__(cls)
-        perspective.last_known_position = None
-        perspective.new_decisions = ()
-        return perspective
-
-    def append(self, *events: Mutates) -> None:
-        self.new_decisions += (*events,)
-
-    def collect_events(self) -> Sequence[Mutates]:
-        collected, self.new_decisions = self.new_decisions, ()
-        return collected
-
-    @property
-    def cb(self) -> list[Selector]:
-        raise NotImplementedError  # pragma: no cover
-
-
-TPerspective = TypeVar("TPerspective", bound=Perspective)
-
-
-given_event_class_mapping: dict[type[Mutates], type[DecoratedFuncCaller]] = {}
-decorated_funcs: dict[tuple[MetaPerspective, type[Mutates]], CallableType] = {}
-
-
-class MetaEnduringObject(SupportsEventDecorator):
+class MetaEnduringObject(MetaSupportsEventDecorator):
     def __init__(
         cls, name: str, bases: tuple[type, ...], namespace: dict[str, Any]
     ) -> None:
@@ -368,7 +368,7 @@ class Selector:
     tags: Sequence[str] = ()
 
 
-class MetaSlice(SupportsEventDecorator):
+class MetaSlice(MetaSupportsEventDecorator):
     pass
 
 

examples/coursebookingdcbslices/application.py

@@ -76,17 +76,18 @@ def __init__(self, name: str, max_courses: int):
         self.max_courses = max_courses
 
     @property
-    def cb(self) -> list[Selector]:
-        return [Selector(types=[StudentRegistered], tags=[self.student_id])]
+    def cb(self) -> Selector:
+        return Selector(types=[StudentRegistered], tags=[self.student_id])
 
     def execute(self) -> None:
-        decision = StudentRegistered(
-            student_id=self.student_id,
-            name=self.name,
-            max_courses=self.max_courses,
-            tags=[self.student_id],
+        self.append(
+            StudentRegistered(
+                student_id=self.student_id,
+                name=self.name,
+                max_courses=self.max_courses,
+                tags=[self.student_id],
+            )
         )
-        self.append(decision)
 
 
 class UpdateStudentName(Slice):
@@ -96,17 +97,16 @@ def __init__(self, student_id: StudentID, name: str) -> None:
         self.student_was_registered: bool = False
 
     @property
-    def cb(self) -> list[Selector]:
-        return [Selector(types=[StudentRegistered, StudentNameUpdated], tags=[self.id])]
+    def cb(self) -> Selector:
+        return Selector(types=[StudentRegistered, StudentNameUpdated], tags=[self.id])
 
     @event(StudentRegistered)
     def _(self) -> None:
         self.student_was_registered = True
 
     def execute(self) -> None:
         assert self.student_was_registered
-        decision = StudentNameUpdated(tags=[self.id], name=self.name)
-        self.append(decision)
+        self.append(StudentNameUpdated(tags=[self.id], name=self.name))
 
 
 class UpdateMaxCourses(Slice):
@@ -116,23 +116,21 @@ def __init__(self, student_id: StudentID, max_courses: int) -> None:
         self.max_courses = max_courses
 
     @property
-    def cb(self) -> list[Selector]:
-        return [
-            Selector(
-                types=[StudentRegistered, StudentMaxCoursesUpdated], tags=[self.id]
-            )
-        ]
+    def cb(self) -> Selector:
+        return Selector(
+            types=[StudentRegistered, StudentMaxCoursesUpdated],
+            tags=[self.id],
+        )
 
     @event(StudentRegistered)
     def _(self) -> None:
         self.student_was_registered = True
 
     def execute(self) -> None:
         assert self.student_was_registered
-        decision = StudentMaxCoursesUpdated(
-            tags=[self.id], max_courses=self.max_courses
+        self.append(
+            StudentMaxCoursesUpdated(tags=[self.id], max_courses=self.max_courses)
         )
-        self.append(decision)
 
 
 class RegisterCourse(Slice):
@@ -142,17 +140,18 @@ def __init__(self, name: str, places: int):
         self.places = places
 
     @property
-    def cb(self) -> list[Selector]:
-        return [Selector(types=[CourseRegistered], tags=[self.course_id])]
+    def cb(self) -> Selector:
+        return Selector(types=[CourseRegistered], tags=[self.course_id])
 
     def execute(self) -> None:
-        decision = CourseRegistered(
-            course_id=self.course_id,
-            name=self.name,
-            places=self.places,
-            tags=[self.course_id],
+        self.append(
+            CourseRegistered(
+                course_id=self.course_id,
+                name=self.name,
+                places=self.places,
+                tags=[self.course_id],
+            )
         )
-        self.append(decision)
 
 
 class UpdateCourseName(Slice):
@@ -162,17 +161,16 @@ def __init__(self, course_id: CourseID, name: str) -> None:
         self.course_was_registered: bool = False
 
     @property
-    def cb(self) -> list[Selector]:
-        return [Selector(types=[CourseRegistered, CourseNameUpdated], tags=[self.id])]
+    def cb(self) -> Selector:
+        return Selector(types=[CourseRegistered, CourseNameUpdated], tags=[self.id])
 
     @event(CourseRegistered)
     def _(self) -> None:
         self.course_was_registered = True
 
     def execute(self) -> None:
         assert self.course_was_registered
-        decision = CourseNameUpdated(tags=[self.id], name=self.name)
-        self.append(decision)
+        self.append(CourseNameUpdated(tags=[self.id], name=self.name))
 
 
 class UpdatePlaces(Slice):
@@ -182,17 +180,16 @@ def __init__(self, course_id: CourseID, places: int) -> None:
         self.course_was_registered: bool = False
 
     @property
-    def cb(self) -> list[Selector]:
-        return [Selector(types=[CourseRegistered, CoursePlacesUpdated], tags=[self.id])]
+    def cb(self) -> Selector:
+        return Selector(types=[CourseRegistered, CoursePlacesUpdated], tags=[self.id])
 
     @event(CourseRegistered)
     def _(self) -> None:
         self.course_was_registered = True
 
     def execute(self) -> None:
         assert self.course_was_registered
-        decision = CoursePlacesUpdated(tags=[self.id], places=self.places)
-        self.append(decision)
+        self.append(CoursePlacesUpdated(tags=[self.id], places=self.places))
 
 
 class StudentJoinsCourse(Slice):
@@ -272,12 +269,13 @@ def execute(self) -> None:
             raise TooManyCoursesError
         if self.student_id in self.students_on_course:
             raise AlreadyJoinedError
-        decision = StudentJoinedCourse(
-            tags=[self.student_id, self.course_id],
-            student_id=self.student_id,
-            course_id=self.course_id,
+        self.append(
+            StudentJoinedCourse(
+                tags=[self.student_id, self.course_id],
+                student_id=self.student_id,
+                course_id=self.course_id,
+            )
         )
-        self.append(decision)
 
 
 class StudentLeavesCourse(Slice):
@@ -291,19 +289,15 @@ def __init__(self, student_id: StudentID, course_id: CourseID) -> None:
 
     @property
     def cb(self) -> list[Selector]:
-        # return [
-        #     Selector(
-        #         types=[StudentRegistered, StudentJoinedCourse, StudentLeftCourse],
-        #         tags=[self.student_id],
-        #     ),
-        #     Selector(
-        #         types=[CourseRegistered, StudentJoinedCourse, StudentLeftCourse],
-        #         tags=[self.course_id],
-        #     ),
-        # ]
         return [
-            Selector(types=type(self).projected_types, tags=[tag])
-            for tag in [self.student_id, self.course_id]
+            Selector(
+                types=[StudentRegistered, StudentJoinedCourse, StudentLeftCourse],
+                tags=[self.student_id],
+            ),
+            Selector(
+                types=[CourseRegistered, StudentJoinedCourse, StudentLeftCourse],
+                tags=[self.course_id],
+            ),
         ]
 
     @event(StudentRegistered)
@@ -335,12 +329,13 @@ def execute(self) -> None:
             raise StudentNotFoundError
         if self.student_id not in self.students_on_course:
             raise NotAlreadyJoinedError
-        decision = StudentLeftCourse(
-            tags=[self.student_id, self.course_id],
-            student_id=self.student_id,
-            course_id=self.course_id,
+        self.append(
+            StudentLeftCourse(
+                tags=[self.student_id, self.course_id],
+                student_id=self.student_id,
+                course_id=self.course_id,
+            )
         )
-        self.append(decision)
 
 
 class StudentsIDs(Slice):
@@ -349,13 +344,17 @@ def __init__(self, course_id: CourseID) -> None:
         self.student_ids: list[StudentID] = []
 
     @property
-    def cb(self) -> list[Selector]:
-        return [Selector(types=type(self).projected_types, tags=[self.course_id])]
+    def cb(self) -> Selector:
+        return Selector(types=type(self).projected_types, tags=[self.course_id])
 
     @event(StudentJoinedCourse)
     def _(self, student_id: StudentID) -> None:
         self.student_ids.append(student_id)
 
+    @event(StudentLeftCourse)
+    def _(self, student_id: StudentID) -> None:
+        self.student_ids.remove(student_id)
+
 
 class StudentNames(Slice):
     def __init__(self, student_ids: list[StudentID]) -> None:
@@ -366,7 +365,6 @@ def __init__(self, student_ids: list[StudentID]) -> None:
     @property
     def cb(self) -> list[Selector]:
         return [
-            # Selector(types=[StudentRegistered, StudentNameUpdated], tags=[student_id])
             Selector(types=type(self).projected_types, tags=[student_id])
             for student_id in self.student_id_names
         ]
@@ -392,14 +390,17 @@ def __init__(self, student_id: StudentID) -> None:
         self.course_ids: list[CourseID] = []
 
     @property
-    def cb(self) -> list[Selector]:
-        # return [Selector(types=[StudentJoinedCourse], tags=[self.student_id])]
-        return [Selector(types=type(self).projected_types, tags=[self.student_id])]
+    def cb(self) -> Selector:
+        return Selector(types=type(self).projected_types, tags=[self.student_id])
 
     @event(StudentJoinedCourse)
     def _(self, course_id: CourseID) -> None:
         self.course_ids.append(course_id)
 
+    @event(StudentLeftCourse)
+    def _(self, course_id: CourseID) -> None:
+        self.course_ids.remove(course_id)
+
 
 class CourseNames(Slice):
     def __init__(self, course_ids: list[CourseID]) -> None:
@@ -410,7 +411,6 @@ def __init__(self, course_ids: list[CourseID]) -> None:
     @property
     def cb(self) -> list[Selector]:
         return [
-            # Selector(types=[CourseRegistered, CourseNameUpdated], tags=[student_id])
             Selector(types=type(self).projected_types, tags=[student_id])
             for student_id in self.course_id_names
         ]
@@ -439,8 +439,8 @@ def __init__(self, student_id: StudentID) -> None:
         self.course_ids: list[CourseID] = []
 
     @property
-    def cb(self) -> list[Selector]:
-        return [Selector(tags=[self.id])]
+    def cb(self) -> Selector:
+        return Selector(tags=[self.id])
 
     @event(StudentRegistered)
     def _(self, name: str, max_courses: int) -> None:
@@ -474,8 +474,8 @@ def __init__(self, course_id: CourseID) -> None:
         self.student_ids: list[StudentID] = []
 
     @property
-    def cb(self) -> list[Selector]:
-        return [Selector(tags=[self.id])]
+    def cb(self) -> Selector:
+        return Selector(tags=[self.id])
 
     @event(CourseRegistered)
     def _(self, name: str, places: int) -> None: