feat: add models module (#109)

* feat: add models module

* docs: add models module

docs/module/models.md

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+# Models
+
+!!! info "Added in `v2.0`"
+
+Reusable SQLAlchemy 2.0 mixins for common column patterns, designed to be composed freely on any `DeclarativeBase` model.
+
+## Overview
+
+The `models` module provides mixins that each add a single, well-defined column behaviour. They work with standard SQLAlchemy 2.0 declarative syntax and are fully compatible with `AsyncSession`.
+
+```python
+from fastapi_toolsets.models import UUIDMixin, TimestampMixin
+
+class Article(Base, UUIDMixin, TimestampMixin):
+    __tablename__ = "articles"
+
+    title: Mapped[str]
+    content: Mapped[str]
+```
+
+All timestamp columns are timezone-aware (`TIMESTAMPTZ`). All defaults are server-side, so they are also applied when inserting rows via raw SQL outside the ORM.
+
+## Mixins
+
+### [`UUIDMixin`](../reference/models.md#fastapi_toolsets.models.UUIDMixin)
+
+Adds a `id: UUID` primary key generated server-side by PostgreSQL using `gen_random_uuid()` (requires PostgreSQL 13+). The value is retrieved via `RETURNING` after insert, so it is available on the Python object immediately after `flush()`.
+
+```python
+from fastapi_toolsets.models import UUIDMixin
+
+class User(Base, UUIDMixin):
+    __tablename__ = "users"
+
+    username: Mapped[str]
+
+# id is None before flush
+user = User(username="alice")
+await session.flush()
+print(user.id)  # UUID('...')
+```
+
+### [`CreatedAtMixin`](../reference/models.md#fastapi_toolsets.models.CreatedAtMixin)
+
+Adds a `created_at: datetime` column set to `NOW()` on insert. The column has no `onupdate` hook — it is intentionally immutable after the row is created.
+
+```python
+from fastapi_toolsets.models import UUIDMixin, CreatedAtMixin
+
+class Order(Base, UUIDMixin, CreatedAtMixin):
+    __tablename__ = "orders"
+
+    total: Mapped[float]
+```
+
+### [`UpdatedAtMixin`](../reference/models.md#fastapi_toolsets.models.UpdatedAtMixin)
+
+Adds an `updated_at: datetime` column set to `NOW()` on insert and automatically updated to `NOW()` on every ORM-level update (via SQLAlchemy's `onupdate` hook).
+
+```python
+from fastapi_toolsets.models import UUIDMixin, UpdatedAtMixin
+
+class Post(Base, UUIDMixin, UpdatedAtMixin):
+    __tablename__ = "posts"
+
+    title: Mapped[str]
+
+post = Post(title="Hello")
+await session.flush()
+await session.refresh(post)
+
+post.title = "Hello World"
+await session.flush()
+await session.refresh(post)
+print(post.updated_at)
+```
+
+!!! note
+    `updated_at` is updated by SQLAlchemy at ORM flush time. If you update rows via raw SQL (e.g. `UPDATE posts SET ...`), the column will **not** be updated automatically — use a database trigger if you need that guarantee.
+
+### [`TimestampMixin`](../reference/models.md#fastapi_toolsets.models.TimestampMixin)
+
+Convenience mixin that combines [`CreatedAtMixin`](../reference/models.md#fastapi_toolsets.models.CreatedAtMixin) and [`UpdatedAtMixin`](../reference/models.md#fastapi_toolsets.models.UpdatedAtMixin). Equivalent to inheriting both.
+
+```python
+from fastapi_toolsets.models import UUIDMixin, TimestampMixin
+
+class Article(Base, UUIDMixin, TimestampMixin):
+    __tablename__ = "articles"
+
+    title: Mapped[str]
+```
+
+## Composing mixins
+
+All mixins can be combined in any order. The only constraint is that exactly one primary key must be defined — either via `UUIDMixin` or directly on the model.
+
+```python
+from fastapi_toolsets.models import UUIDMixin, TimestampMixin
+
+class Event(Base, UUIDMixin, TimestampMixin):
+    __tablename__ = "events"
+    name: Mapped[str]
+
+class Counter(Base, UpdatedAtMixin):
+    __tablename__ = "counters"
+    id: Mapped[int] = mapped_column(primary_key=True, autoincrement=True)
+    value: Mapped[int]
+```
+
+---
+
+[:material-api: API Reference](../reference/models.md)

docs/reference/models.md

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+# `models`
+
+Here's the reference for the SQLAlchemy model mixins provided by the `models` module.
+
+You can import them directly from `fastapi_toolsets.models`:
+
+```python
+from fastapi_toolsets.models import (
+    UUIDMixin,
+    CreatedAtMixin,
+    UpdatedAtMixin,
+    TimestampMixin,
+)
+```
+
+## ::: fastapi_toolsets.models.UUIDMixin
+
+## ::: fastapi_toolsets.models.CreatedAtMixin
+
+## ::: fastapi_toolsets.models.UpdatedAtMixin
+
+## ::: fastapi_toolsets.models.TimestampMixin

src/fastapi_toolsets/models.py

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+"""SQLAlchemy model mixins for common column patterns."""
+
+import uuid
+from datetime import datetime
+
+from sqlalchemy import DateTime, Uuid, func, text
+from sqlalchemy.orm import Mapped, mapped_column
+
+__all__ = [
+    "UUIDMixin",
+    "CreatedAtMixin",
+    "UpdatedAtMixin",
+    "TimestampMixin",
+]
+
+
+class UUIDMixin:
+    """Mixin that adds a UUID primary key auto-generated by the database."""
+
+    id: Mapped[uuid.UUID] = mapped_column(
+        Uuid,
+        primary_key=True,
+        server_default=text("gen_random_uuid()"),
+    )
+
+
+class CreatedAtMixin:
+    """Mixin that adds a ``created_at`` timestamp column."""
+
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True),
+        server_default=func.now(),
+    )
+
+
+class UpdatedAtMixin:
+    """Mixin that adds an ``updated_at`` timestamp column."""
+
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True),
+        server_default=func.now(),
+        onupdate=func.now(),
+    )
+
+
+class TimestampMixin(CreatedAtMixin, UpdatedAtMixin):
+    """Mixin that combines ``created_at`` and ``updated_at`` timestamp columns."""

tests/test_models.py

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+"""Tests for fastapi_toolsets.models mixins."""
+
+import uuid
+
+import pytest
+from sqlalchemy import String
+from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
+from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_column
+
+from fastapi_toolsets.models import (
+    CreatedAtMixin,
+    TimestampMixin,
+    UUIDMixin,
+    UpdatedAtMixin,
+)
+
+from .conftest import DATABASE_URL
+
+
+class MixinBase(DeclarativeBase):
+    pass
+
+
+class UUIDModel(MixinBase, UUIDMixin):
+    __tablename__ = "mixin_uuid_models"
+
+    name: Mapped[str] = mapped_column(String(50))
+
+
+class UpdatedAtModel(MixinBase, UpdatedAtMixin):
+    __tablename__ = "mixin_updated_at_models"
+
+    id: Mapped[int] = mapped_column(primary_key=True, autoincrement=True)
+    name: Mapped[str] = mapped_column(String(50))
+
+
+class CreatedAtModel(MixinBase, CreatedAtMixin):
+    __tablename__ = "mixin_created_at_models"
+
+    id: Mapped[int] = mapped_column(primary_key=True, autoincrement=True)
+    name: Mapped[str] = mapped_column(String(50))
+
+
+class TimestampModel(MixinBase, TimestampMixin):
+    __tablename__ = "mixin_timestamp_models"
+
+    id: Mapped[int] = mapped_column(primary_key=True, autoincrement=True)
+    name: Mapped[str] = mapped_column(String(50))
+
+
+class FullMixinModel(MixinBase, UUIDMixin, UpdatedAtMixin):
+    __tablename__ = "mixin_full_models"
+
+    name: Mapped[str] = mapped_column(String(50))
+
+
+@pytest.fixture(scope="function")
+async def mixin_session():
+    engine = create_async_engine(DATABASE_URL, echo=False)
+    async with engine.begin() as conn:
+        await conn.run_sync(MixinBase.metadata.create_all)
+
+    session_factory = async_sessionmaker(engine, expire_on_commit=False)
+    session = session_factory()
+
+    try:
+        yield session
+    finally:
+        await session.close()
+        async with engine.begin() as conn:
+            await conn.run_sync(MixinBase.metadata.drop_all)
+        await engine.dispose()
+
+
+class TestUUIDMixin:
+    @pytest.mark.anyio
+    async def test_uuid_generated_by_db(self, mixin_session):
+        """UUID is generated server-side and populated after flush."""
+        obj = UUIDModel(name="test")
+        mixin_session.add(obj)
+        await mixin_session.flush()
+
+        assert obj.id is not None
+        assert isinstance(obj.id, uuid.UUID)
+
+    @pytest.mark.anyio
+    async def test_uuid_is_primary_key(self):
+        """UUIDMixin adds id as primary key column."""
+        pk_cols = [c.name for c in UUIDModel.__table__.primary_key]
+        assert pk_cols == ["id"]
+
+    @pytest.mark.anyio
+    async def test_each_row_gets_unique_uuid(self, mixin_session):
+        """Each inserted row gets a distinct UUID."""
+        a = UUIDModel(name="a")
+        b = UUIDModel(name="b")
+        mixin_session.add_all([a, b])
+        await mixin_session.flush()
+
+        assert a.id != b.id
+
+    @pytest.mark.anyio
+    async def test_uuid_server_default_set(self):
+        """Column has gen_random_uuid() as server default."""
+        col = UUIDModel.__table__.c["id"]
+        assert col.server_default is not None
+        assert "gen_random_uuid" in str(col.server_default.arg)
+
+
+class TestUpdatedAtMixin:
+    @pytest.mark.anyio
+    async def test_updated_at_set_on_insert(self, mixin_session):
+        """updated_at is populated after insert."""
+        obj = UpdatedAtModel(name="initial")
+        mixin_session.add(obj)
+        await mixin_session.flush()
+        await mixin_session.refresh(obj)
+
+        assert obj.updated_at is not None
+        assert obj.updated_at.tzinfo is not None  # timezone-aware
+
+    @pytest.mark.anyio
+    async def test_updated_at_changes_on_update(self, mixin_session):
+        """updated_at is updated when the row is modified."""
+        obj = UpdatedAtModel(name="initial")
+        mixin_session.add(obj)
+        await mixin_session.flush()
+        await mixin_session.refresh(obj)
+
+        original_ts = obj.updated_at
+
+        obj.name = "modified"
+        await mixin_session.flush()
+        await mixin_session.refresh(obj)
+
+        assert obj.updated_at >= original_ts
+
+    @pytest.mark.anyio
+    async def test_updated_at_column_is_not_nullable(self):
+        """updated_at column is non-nullable."""
+        col = UpdatedAtModel.__table__.c["updated_at"]
+        assert not col.nullable
+
+    @pytest.mark.anyio
+    async def test_updated_at_has_server_default(self):
+        """updated_at column has a server-side default."""
+        col = UpdatedAtModel.__table__.c["updated_at"]
+        assert col.server_default is not None
+
+    @pytest.mark.anyio
+    async def test_updated_at_has_onupdate(self):
+        """updated_at column has an onupdate clause."""
+        col = UpdatedAtModel.__table__.c["updated_at"]
+        assert col.onupdate is not None
+
+
+class TestCreatedAtMixin:
+    @pytest.mark.anyio
+    async def test_created_at_set_on_insert(self, mixin_session):
+        """created_at is populated after insert."""
+        obj = CreatedAtModel(name="new")
+        mixin_session.add(obj)
+        await mixin_session.flush()
+        await mixin_session.refresh(obj)
+
+        assert obj.created_at is not None
+        assert obj.created_at.tzinfo is not None  # timezone-aware
+
+    @pytest.mark.anyio
+    async def test_created_at_not_changed_on_update(self, mixin_session):
+        """created_at is not modified when the row is updated."""
+        obj = CreatedAtModel(name="original")
+        mixin_session.add(obj)
+        await mixin_session.flush()
+        await mixin_session.refresh(obj)
+
+        original_ts = obj.created_at
+
+        obj.name = "updated"
+        await mixin_session.flush()
+        await mixin_session.refresh(obj)
+
+        assert obj.created_at == original_ts
+
+    @pytest.mark.anyio
+    async def test_created_at_column_is_not_nullable(self):
+        """created_at column is non-nullable."""
+        col = CreatedAtModel.__table__.c["created_at"]
+        assert not col.nullable
+
+    @pytest.mark.anyio
+    async def test_created_at_has_no_onupdate(self):
+        """created_at column has no onupdate clause."""
+        col = CreatedAtModel.__table__.c["created_at"]
+        assert col.onupdate is None
+
+
+class TestTimestampMixin:
+    @pytest.mark.anyio
+    async def test_both_columns_set_on_insert(self, mixin_session):
+        """created_at and updated_at are both populated after insert."""
+        obj = TimestampModel(name="new")
+        mixin_session.add(obj)
+        await mixin_session.flush()
+        await mixin_session.refresh(obj)
+
+        assert obj.created_at is not None
+        assert obj.updated_at is not None
+
+    @pytest.mark.anyio
+    async def test_created_at_stable_updated_at_changes_on_update(self, mixin_session):
+        """On update: created_at stays the same, updated_at advances."""
+        obj = TimestampModel(name="original")
+        mixin_session.add(obj)
+        await mixin_session.flush()
+        await mixin_session.refresh(obj)
+
+        original_created = obj.created_at
+        original_updated = obj.updated_at
+
+        obj.name = "modified"
+        await mixin_session.flush()
+        await mixin_session.refresh(obj)
+
+        assert obj.created_at == original_created
+        assert obj.updated_at >= original_updated
+
+    @pytest.mark.anyio
+    async def test_timestamp_mixin_has_both_columns(self):
+        """TimestampModel exposes both created_at and updated_at columns."""
+        col_names = {c.name for c in TimestampModel.__table__.columns}
+        assert "created_at" in col_names
+        assert "updated_at" in col_names
+
+
+class TestFullMixinModel:
+    @pytest.mark.anyio
+    async def test_combined_mixins_work_together(self, mixin_session):
+        """UUIDMixin and UpdatedAtMixin can be combined on the same model."""
+        obj = FullMixinModel(name="combined")
+        mixin_session.add(obj)
+        await mixin_session.flush()
+        await mixin_session.refresh(obj)
+
+        assert isinstance(obj.id, uuid.UUID)
+        assert obj.updated_at is not None
+        assert obj.updated_at.tzinfo is not None