Implement BaseModel class, TimestampMixin, TzDateTime type; cleanup Task model

migrations/env.py

@@ -26,16 +26,22 @@ def process_revision_directives(_context, _revision, directives):
         directives[:] = []
 
 
+context_parameters = {
+    'target_metadata': BaseModel.metadata,
+    'process_revision_directives': process_revision_directives,
+    'user_module_prefix': 'tofu_types.',
+}
+
+
 def run_migrations_offline():
     """
     Run migrations in 'offline' mode, which does not require an actual database engine and can be used to generate SQL scripts.
     """
     context.configure(
         url=app.config.sqlalchemy_database_uri,
-        target_metadata=BaseModel.metadata,
-        process_revision_directives=process_revision_directives,
         literal_binds=True,
         dialect_opts={"paramstyle": "named"},
+        **context_parameters,
     )
 
     with context.begin_transaction():
@@ -49,8 +55,7 @@ def run_migrations_online():
     with db.engine.connect() as connection:
         context.configure(
             connection=connection,
-            target_metadata=BaseModel.metadata,
+            **context_parameters,
-            process_revision_directives=process_revision_directives,
         )
 
         with context.begin_transaction():

migrations/script.py.mako

@@ -8,6 +8,8 @@ Create Date: ${create_date}
 
 from alembic import op
 import sqlalchemy as sa
+
+import tofu_api.common.database.types as tofu_types
 ${imports if imports else ""}
 
 # Revision identifiers, used by Alembic.

migrations/versions/2022_04_15_2141-044f3afd19b0_initial_revision.py

@@ -1,16 +1,18 @@
 """
 Initial revision
 
-Revision ID: 716726b4a1fe
+Revision ID: 044f3afd19b0
 Revises: 
-Create Date: 2022-04-15 16:05:29.358429+02:00
+Create Date: 2022-04-15 21:41:39.962542+02:00
 """
 
 from alembic import op
 import sqlalchemy as sa
 
+import tofu_api.common.database.types as tofu_types
+
 # Revision identifiers, used by Alembic.
-revision = '716726b4a1fe'
+revision = '044f3afd19b0'
 down_revision = None
 branch_labels = None
 depends_on = None
@@ -19,16 +21,18 @@ depends_on = None
 def upgrade():
     # ### commands auto generated by Alembic - please adjust! ###
     op.create_table(
-        'tasks',
+        'task',
         sa.Column('id', sa.Integer(), nullable=False),
+        sa.Column('created_at', tofu_types.TzDateTime(), server_default=sa.text('now()'), nullable=False),
+        sa.Column('modified_at', tofu_types.TzDateTime(), server_default=sa.text('now()'), nullable=False),
         sa.Column('title', sa.String(length=255), nullable=False),
         sa.Column('description', sa.Text(), nullable=False),
-        sa.PrimaryKeyConstraint('id', name=op.f('pk_tasks'))
+        sa.PrimaryKeyConstraint('id', name=op.f('pk_task'))
     )
     # ### end Alembic commands ###
 
 
 def downgrade():
     # ### commands auto generated by Alembic - please adjust! ###
-    op.drop_table('tasks')
+    op.drop_table('task')
     # ### end Alembic commands ###

tofu_api/app.py

@@ -6,6 +6,7 @@ from flask import Flask
 
 from tofu_api.api import TofuApiBlueprint
 from tofu_api.common.config import Config
+from tofu_api.common.json import JSONEncoder
 from tofu_api.dependencies import Dependencies
 
 # Enable deprecation warnings in dev environment
@@ -19,6 +20,7 @@ class App(Flask):
     """
     # Override Flask classes
     config_class = Config
+    json_encoder = JSONEncoder
 
     # Set type hint for config
     config: Config
@@ -57,7 +59,7 @@ class App(Flask):
         db = self.dependencies.get_sqlalchemy()
         db.init_database(self)
 
-        # Import models to fill the metadata object
+        # Import models to populate the database metadata
         import tofu_api.models  # noqa (unused import)
 
 

tofu_api/common/database/__init__.py

@@ -1 +1,3 @@
+from .metadata import MetaData
 from .sqlalchemy import SQLAlchemy
+from .typing import Col, Rel

tofu_api/common/database/metadata.py

@@ -0,0 +1,25 @@
+from sqlalchemy import MetaData as _MetaData
+
+__all__ = [
+    'MetaData',
+]
+
+
+class MetaData(_MetaData):
+    """
+    App specific subclass of the SQLAlchemy MetaData class.
+    """
+
+    # Define naming convention for constraints
+    _naming_convention = {
+        "ix": 'ix_%(column_0_label)s',
+        "uq": "uq_%(table_name)s_%(column_0_name)s",
+        "ck": "ck_%(table_name)s_%(constraint_name)s",
+        "fk": "fk_%(table_name)s_%(column_0_name)s_%(referred_table_name)s",
+        "pk": "pk_%(table_name)s"
+    }
+
+    def __init__(self, *args, naming_convention=None, **kwargs):
+        if not naming_convention:
+            naming_convention = self._naming_convention
+        super().__init__(*args, naming_convention=naming_convention, **kwargs)

tofu_api/common/database/mixins.py

@@ -0,0 +1,23 @@
+from datetime import datetime
+
+from sqlalchemy import Column, func
+from sqlalchemy.orm import declarative_mixin
+
+from tofu_api.common.database import Col
+from tofu_api.common.database.types import TzDateTime
+
+__all__ = [
+    'TimestampMixin'
+]
+
+
+@declarative_mixin
+class TimestampMixin:
+    """
+    Mixin for database models that provides the "created_at" and "modified_at" columns.
+    """
+    # Created timestamp (automatically set to NOW() once on object creation)
+    created_at: Col[datetime] = Column(TzDateTime, nullable=False, server_default=func.now())
+
+    # Modified timestamp (automatically set to NOW() on each update)
+    modified_at: Col[datetime] = Column(TzDateTime, nullable=False, server_default=func.now(), onupdate=func.now())

tofu_api/common/database/types/__init__.py

@@ -0,0 +1 @@
+from .tz_date_time import TzDateTime

tofu_api/common/database/types/tz_date_time.py

@@ -0,0 +1,39 @@
+from datetime import datetime, timezone
+
+from sqlalchemy import DateTime, TypeDecorator
+
+__all__ = [
+    'TzDateTime',
+]
+
+
+class TzDateTime(TypeDecorator):
+    """
+    Custom SQLAlchemy data type for timezone aware datetimes.
+    """
+    impl = DateTime
+    cache_ok = True
+
+    @property
+    def python_type(self):
+        return datetime
+
+    def process_bind_param(self, value: datetime, dialect):
+        """
+        Convert a datetime object that is bound to a query parameter.
+        """
+        if value is not None and value.tzinfo:
+            value = value.astimezone(timezone.utc).replace(tzinfo=None)
+        return value
+
+    def process_result_value(self, value: datetime, dialect):
+        """
+        Convert a datetime object from a query result.
+        """
+        return value.replace(tzinfo=timezone.utc) if value is not None else None
+
+    def process_literal_param(self, value: datetime, dialect):
+        """
+        Convert a literal parameter value to be rendered inline within a statement.
+        """
+        return self.process_bind_param(value, dialect)

tofu_api/common/database/typing.py

@@ -0,0 +1,14 @@
+from typing import TypeVar, Union
+
+from sqlalchemy import Column
+from sqlalchemy.orm import RelationshipProperty
+
+__all__ = [
+    'Col',
+    'Rel',
+]
+
+# Define type aliases for SQLAlchemy columns and relationships in declarative models
+_T = TypeVar('_T')
+Col = Union[Column, _T]
+Rel = Union[RelationshipProperty, _T]

tofu_api/common/json/__init__.py

@@ -0,0 +1 @@
+from .json_encoder import JSONEncoder

tofu_api/common/json/json_encoder.py

@@ -0,0 +1,29 @@
+from datetime import datetime
+from typing import Any
+
+from flask.json import JSONEncoder as _FlaskJSONEncoder
+
+__all__ = [
+    'JSONEncoder',
+]
+
+
+class JSONEncoder(_FlaskJSONEncoder):
+    """
+    Custom JSON encoder built on top of the Flask JSONEncoder class.
+    """
+
+    def default(self, obj: Any) -> Any:
+        """
+        Convert any object to a JSON serializable type.
+        """
+        # Convert datetimes to ISO format without microseconds (e.g. '2022-01-02T10:20:30+00:00')
+        if isinstance(obj, datetime):
+            return obj.isoformat(timespec='seconds')
+
+        # Use to_dict() method on objects that have it
+        if hasattr(obj, 'to_dict'):
+            return obj.to_dict()
+
+        # Fallback to the Flask JSONEncoder
+        return super().default(obj)

tofu_api/models/__init__.py

@@ -1,5 +1,5 @@
 # Base model first
-from .base import metadata, BaseModel
+from .base import BaseModel
 
 # Data models
 from .task import Task

tofu_api/models/base.py

@@ -1,22 +1,62 @@
-from sqlalchemy import MetaData
+from typing import Any, Iterable, Optional
-from sqlalchemy.orm import declarative_base
+
+from sqlalchemy import Column, Integer, inspect
+from sqlalchemy.orm import InstanceState, as_declarative
+
+from tofu_api.common.database import Col, MetaData
 
 __all__ = [
-    'metadata',
     'BaseModel',
 ]
 
-# Define naming convention for constraints
-_naming_convention = {
-    "ix": 'ix_%(column_0_label)s',
-    "uq": "uq_%(table_name)s_%(column_0_name)s",
-    "ck": "ck_%(table_name)s_%(constraint_name)s",
-    "fk": "fk_%(table_name)s_%(column_0_name)s_%(referred_table_name)s",
-    "pk": "pk_%(table_name)s"
-}
 
-# Create metadata object for database schemas
+@as_declarative(name='BaseModel', metadata=MetaData())
-metadata = MetaData(naming_convention=_naming_convention)
+class BaseModel:
+    """
+    Declarative base class for database models.
+    """
 
-# Generate declarative base class for database models
+    # Default primary key
-BaseModel = declarative_base(name='BaseModel', metadata=metadata)
+    id: Col[int] = Column(Integer, nullable=False, primary_key=True)
+
+    def __repr__(self) -> str:
+        """
+        Return a string representation of this object.
+        """
+        return self._repr(id=self.id) if hasattr(self, 'id') else self._repr()
+
+    def _repr(self, **fields) -> str:
+        """
+        Helper method for implementing __repr__.
+        """
+        state: InstanceState = inspect(self)
+        state_str = f' [transient {id(self)}]' if state.transient \
+            else f' [pending {id(self)}]' if state.pending \
+            else ' [deleted]' if state.deleted \
+            else ' [detached]' if state.detached else ''
+        param_str = ', '.join([f'{key}={value!r}' for key, value in fields.items()] if fields else state.identity or [])
+        return f'<{type(self).__name__}({param_str}){state_str}>'
+
+    def to_dict(
+        self,
+        *,
+        fields: Optional[Iterable[str]] = None,
+        exclude: Optional[Iterable[str]] = None,
+    ) -> dict[str, Any]:
+        """
+        Return the object's data as a dictionary.
+
+        By default, the dictionary will contain all table columns (with their column name as key) defined in the model. This can be
+        overridden by setting the `fields` and/or `exclude` parameters, in which case only fields that are listed in `fields` will be
+        included in the dictionary, except for fields listed in `exclude`.
+        """
+        # Determine fields to include in dictionary (starting will all table columns)
+        included_fields = set(column.name for column in self.__table__.columns)
+        if fields is not None:
+            included_fields.intersection_update(fields)
+        if exclude is not None:
+            included_fields.difference_update(exclude)
+
+        return {
+            field: getattr(self, field) for field in included_fields
+        }

tofu_api/models/task.py

@@ -1,25 +1,19 @@
-from sqlalchemy import Column, Integer, String, Text
+from sqlalchemy import Column, String, Text
 
+from tofu_api.common.database import Col
+from tofu_api.common.database.mixins import TimestampMixin
 from .base import BaseModel
 
 
-class Task(BaseModel):
+class Task(TimestampMixin, BaseModel):
     """
     Database model for tasks.
     """
 
-    __tablename__ = 'tasks'
+    __tablename__ = 'task'
 
-    id: int = Column(Integer, nullable=False, primary_key=True)
+    title: Col[str] = Column(String(255), nullable=False)
-    # TODO: created_at, modified_at
+    description: Col[str] = Column(Text, nullable=False, default='')
 
-    title: str = Column(String(255), nullable=False)
+    def __repr__(self):
-    description: str = Column(Text, nullable=False, default='')
+        return self._repr(id=self.id, title=self.title)
-
-    def to_dict(self) -> dict:
-        # TODO: Implement a generic to_dict() in the base model
-        return {
-            'id': self.id,
-            'title': self.title,
-            'description': self.description,
-        }