Add Postgres table adapter with TableRepositoryInterface.

Introduce PostgresAdapter for dict-based row CRUD via psycopg3, including config, lazy exports, unit/integration tests with testcontainers, and an example UserTableRepository.

Co-authored-by: Cursor <[email protected]>

tests/unit/adapters_test.py

@@ -45,6 +45,7 @@ from python_repositories import JsonRepositoryInterface
 assert JsonRepositoryInterface is not None
 assert "python_repositories.adapters.redis_adapter" not in sys.modules
 assert "python_repositories.adapters.minio_adapter" not in sys.modules
+assert "python_repositories.adapters.postgres_adapter" not in sys.modules
 """
     result = subprocess.run(
         [sys.executable, "-c", script],
@@ -58,10 +59,11 @@ assert "python_repositories.adapters.minio_adapter" not in sys.modules
 
 def test_lazy_adapter_load_succeeds_when_extra_present() -> None:
     """Adapters load when their optional dependencies are installed."""
-    from python_repositories import MinioAdapter, RedisAdapter
+    from python_repositories import MinioAdapter, PostgresAdapter, RedisAdapter
 
     assert RedisAdapter.__name__ == "RedisAdapter"
     assert MinioAdapter.__name__ == "MinioAdapter"
+    assert PostgresAdapter.__name__ == "PostgresAdapter"
 
 
 def test_redis_adapter_import_error_without_extra() -> None:
@@ -86,6 +88,17 @@ def test_minio_adapter_import_error_without_extra() -> None:
     importlib.reload(minio_adapter_module)
 
 
+def test_postgres_adapter_import_error_without_extra() -> None:
+    """Missing postgres extra raises ImportError with install hint."""
+    import python_repositories.adapters.postgres_adapter as postgres_adapter_module
+
+    with patch.object(builtins, "__import__", new=_block_backend_import("psycopg")):
+        with pytest.raises(ImportError, match=r"python-repositories\[postgres\]"):
+            importlib.reload(postgres_adapter_module)
+
+    importlib.reload(postgres_adapter_module)
+
+
 def test_top_level_lazy_import_propagates_redis_import_error() -> None:
     """Top-level RedisAdapter access surfaces adapter import errors."""
     with patch(
@@ -112,6 +125,19 @@ def test_top_level_lazy_import_propagates_minio_import_error() -> None:
             _ = python_repositories.MinioAdapter
 
 
+def test_top_level_lazy_import_propagates_postgres_import_error() -> None:
+    """Top-level PostgresAdapter access surfaces adapter import errors."""
+    with patch(
+        "importlib.import_module",
+        side_effect=ImportError(
+            "Postgres support requires the postgres extra. "
+            "Install with: pip install python-repositories[postgres]"
+        ),
+    ):
+        with pytest.raises(ImportError, match=r"python-repositories\[postgres\]"):
+            _ = python_repositories.PostgresAdapter
+
+
 def test_adapters_subpackage_lazy_import_succeeds() -> None:
     """Adapter subpackage imports delegate to the same lazy loader."""
     from python_repositories.adapters import RedisAdapter
@@ -123,7 +149,7 @@ def test_adapters_dir_exposes_lazy_exports() -> None:
     """dir(adapters) includes lazy adapter names for tab completion."""
     import python_repositories.adapters as adapters
 
-    assert {"RedisAdapter", "MinioAdapter"}.issubset(set(dir(adapters)))
+    assert {"RedisAdapter", "MinioAdapter", "PostgresAdapter"}.issubset(set(dir(adapters)))
 
 
 def test_adapters_getattr_raises_for_unknown() -> None:
@@ -138,3 +164,4 @@ def test_top_level_dir_exposes_lazy_exports() -> None:
     """dir(python_repositories) includes lazy adapter names for tab completion."""
     assert "RedisAdapter" in dir(python_repositories)
     assert "MinioAdapter" in dir(python_repositories)
+    assert "PostgresAdapter" in dir(python_repositories)

tests/unit/conftest.py

@@ -5,12 +5,14 @@ from __future__ import annotations
 from unittest.mock import MagicMock
 
 from minio import Minio
+import psycopg
 import pytest
 import redis
 
 from python_repositories.adapters.minio_adapter import MinioAdapter
+from python_repositories.adapters.postgres_adapter import PostgresAdapter
 from python_repositories.adapters.redis_adapter import RedisAdapter
-from tests.conftest import TEST_MINIO_CONFIG, TEST_REDIS_CONFIG
+from tests.conftest import TEST_MINIO_CONFIG, TEST_POSTGRES_CONFIG, TEST_REDIS_CONFIG
 
 
 @pytest.fixture
@@ -25,3 +27,14 @@ def minio_adapter() -> MinioAdapter:
     """Provide a MinioAdapter with an injected mock client."""
     mock_client = MagicMock(spec=Minio)
     return MinioAdapter(config=TEST_MINIO_CONFIG, client=mock_client)
+
+
+@pytest.fixture
+def postgres_adapter() -> PostgresAdapter:
+    """Provide a PostgresAdapter with an injected mock client."""
+    mock_client = MagicMock(spec=psycopg.Connection)
+    mock_cursor = MagicMock()
+    mock_cursor.__enter__ = MagicMock(return_value=mock_cursor)
+    mock_cursor.__exit__ = MagicMock(return_value=False)
+    mock_client.cursor.return_value = mock_cursor
+    return PostgresAdapter(config=TEST_POSTGRES_CONFIG, client=mock_client)

tests/unit/connection_aware_adapter_test.py

@@ -6,10 +6,12 @@ from typing import cast
 from unittest.mock import MagicMock, patch
 
 import redis
+import psycopg
 
 from python_repositories.adapters.minio_adapter import MinioAdapter
+from python_repositories.adapters.postgres_adapter import PostgresAdapter
 from python_repositories.adapters.redis_adapter import RedisAdapter
-from tests.conftest import TEST_MINIO_CONFIG, TEST_REDIS_CONFIG
+from tests.conftest import TEST_MINIO_CONFIG, TEST_POSTGRES_CONFIG, TEST_REDIS_CONFIG
 
 
 class TestRedisConnectionHealth:
@@ -161,3 +163,74 @@ class TestMinioConnectionHealth:
             assert reinjected.is_connected()
 
         assert mock_client.bucket_exists.call_count == 2
+
+
+class TestPostgresConnectionHealth:
+    def test_not_connected_when_no_client(self) -> None:
+        adapter = PostgresAdapter(config=TEST_POSTGRES_CONFIG)
+        assert not adapter.is_connected()
+
+    def test_connected_when_probe_succeeds(
+        self, postgres_adapter: PostgresAdapter
+    ) -> None:
+        assert postgres_adapter.is_connected()
+        cast(MagicMock, postgres_adapter._client).cursor.assert_called()
+
+    def test_stale_connection_when_probe_fails(
+        self, postgres_adapter: PostgresAdapter
+    ) -> None:
+        mock_cursor = cast(MagicMock, postgres_adapter._client).cursor.return_value
+        mock_cursor.execute.side_effect = psycopg.OperationalError("connection lost")
+
+        assert not postgres_adapter.is_connected()
+
+    def test_cache_hit_avoids_second_probe(
+        self, postgres_adapter: PostgresAdapter
+    ) -> None:
+        mock_client = cast(MagicMock, postgres_adapter._client)
+
+        with patch(
+            "python_repositories.adapters.connection_aware_adapter.time.monotonic",
+            return_value=100.0,
+        ):
+            assert postgres_adapter.is_connected()
+            assert postgres_adapter.is_connected()
+
+        assert mock_client.cursor.call_count == 1
+
+    def test_cache_miss_runs_probe_again(
+        self, postgres_adapter: PostgresAdapter
+    ) -> None:
+        mock_client = cast(MagicMock, postgres_adapter._client)
+
+        with patch(
+            "python_repositories.adapters.connection_aware_adapter.time.monotonic",
+            side_effect=[100.0, 102.0],
+        ):
+            assert postgres_adapter.is_connected()
+            assert postgres_adapter.is_connected()
+
+        assert mock_client.cursor.call_count == 2
+
+    def test_disconnect_clears_cache(self, postgres_adapter: PostgresAdapter) -> None:
+        mock_client = cast(MagicMock, postgres_adapter._client)
+
+        with patch(
+            "python_repositories.adapters.connection_aware_adapter.time.monotonic",
+            return_value=100.0,
+        ):
+            assert postgres_adapter.is_connected()
+
+        postgres_adapter.disconnect()
+        reinjected = PostgresAdapter(
+            config=postgres_adapter._config,
+            client=mock_client,
+        )
+
+        with patch(
+            "python_repositories.adapters.connection_aware_adapter.time.monotonic",
+            return_value=100.0,
+        ):
+            assert reinjected.is_connected()
+
+        assert mock_client.cursor.call_count == 2

tests/unit/postgres_adapter_test.py

@@ -0,0 +1,235 @@
+"""Unit tests for PostgresAdapter instantiation and injection."""
+
+from __future__ import annotations
+
+from unittest.mock import MagicMock
+
+import psycopg
+import pytest
+
+from python_repositories.adapters.postgres_adapter import PostgresAdapter
+from python_repositories.interfaces import TableRepositoryInterface
+from tests.conftest import TEST_POSTGRES_CONFIG
+
+
+def _mock_cursor() -> MagicMock:
+    mock_cursor = MagicMock()
+    mock_cursor.__enter__ = MagicMock(return_value=mock_cursor)
+    mock_cursor.__exit__ = MagicMock(return_value=False)
+    return mock_cursor
+
+
+def _mock_client(*, probe_raises: Exception | None = None) -> MagicMock:
+    mock_client = MagicMock(spec=psycopg.Connection)
+    mock_cursor = _mock_cursor()
+    if probe_raises is not None:
+        mock_cursor.execute.side_effect = probe_raises
+    mock_client.cursor.return_value = mock_cursor
+    return mock_client
+
+
+def test_should_adhere_to_interface() -> None:
+    assert issubclass(PostgresAdapter, TableRepositoryInterface)
+    _ = PostgresAdapter(config=TEST_POSTGRES_CONFIG)
+
+
+def test_should_have_logger_when_instantiated() -> None:
+    adapter = PostgresAdapter(config=TEST_POSTGRES_CONFIG)
+    assert hasattr(adapter, "logger")
+    assert adapter.logger is not None
+
+
+def test_should_not_be_connected_when_instantiated() -> None:
+    adapter = PostgresAdapter(config=TEST_POSTGRES_CONFIG)
+    assert adapter._client is None
+    assert not adapter.is_connected()
+
+
+def test_constructs_with_injected_config_without_env(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    monkeypatch.delenv("POSTGRES_URI", raising=False)
+    monkeypatch.delenv("POSTGRES_TABLE", raising=False)
+    adapter = PostgresAdapter(config=TEST_POSTGRES_CONFIG)
+    assert adapter._config == TEST_POSTGRES_CONFIG
+
+
+def test_constructs_with_injected_client_without_env(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    monkeypatch.delenv("POSTGRES_URI", raising=False)
+    monkeypatch.delenv("POSTGRES_TABLE", raising=False)
+    mock_client = _mock_client()
+    adapter = PostgresAdapter(config=TEST_POSTGRES_CONFIG, client=mock_client)
+    assert adapter._client is mock_client
+    assert adapter._client_injected is True
+
+
+def test_raises_when_client_provided_without_config() -> None:
+    mock_client = MagicMock(spec=psycopg.Connection)
+    with pytest.raises(ValueError, match="config is required"):
+        PostgresAdapter(client=mock_client)
+
+
+def test_disconnect_does_not_close_injected_client() -> None:
+    mock_client = _mock_client()
+    adapter = PostgresAdapter(config=TEST_POSTGRES_CONFIG, client=mock_client)
+    adapter.disconnect()
+    mock_client.close.assert_not_called()
+    assert adapter._client is None
+
+
+class CustomEnvPostgresAdapter(PostgresAdapter):
+    uri_env_var_name = "CUSTOM_POSTGRES_URI"
+    table_env_var_name = "CUSTOM_POSTGRES_TABLE"
+    primary_key_env_var_name = "CUSTOM_POSTGRES_PRIMARY_KEY"
+
+
+def test_subclass_custom_env_var_names(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setenv("CUSTOM_POSTGRES_URI", "postgresql://custom/mydb")
+    monkeypatch.setenv("CUSTOM_POSTGRES_TABLE", "items")
+    monkeypatch.setenv("CUSTOM_POSTGRES_PRIMARY_KEY", "item_id")
+    adapter = CustomEnvPostgresAdapter()
+    assert adapter._config.uri == "postgresql://custom/mydb"
+    assert adapter._config.table == "items"
+    assert adapter._config.primary_key == "item_id"
+
+
+def test_connect_with_injected_client_succeeds_when_probe_ok() -> None:
+    mock_client = _mock_client()
+    adapter = PostgresAdapter(config=TEST_POSTGRES_CONFIG, client=mock_client)
+
+    adapter.connect()
+
+    assert mock_client.cursor.return_value.execute.call_count == 2
+
+
+def test_connect_with_injected_client_raises_on_probe_failure() -> None:
+    mock_client = _mock_client(probe_raises=psycopg.OperationalError("connection lost"))
+    adapter = PostgresAdapter(config=TEST_POSTGRES_CONFIG, client=mock_client)
+
+    with pytest.raises(ConnectionError, match="Could not connect to Postgres"):
+        adapter.connect()
+
+
+def test_connect_with_injected_client_skips_validation_when_client_cleared() -> None:
+    mock_client = _mock_client()
+    adapter = PostgresAdapter(config=TEST_POSTGRES_CONFIG, client=mock_client)
+    adapter.disconnect()
+
+    adapter.connect()
+
+    mock_client.cursor.assert_not_called()
+
+
+def test_connect_reconnects_when_existing_client_unhealthy(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    stale_client = _mock_client(probe_raises=psycopg.OperationalError("connection lost"))
+    new_client = _mock_client()
+    adapter = PostgresAdapter(config=TEST_POSTGRES_CONFIG)
+    adapter._client = stale_client
+
+    monkeypatch.setattr("psycopg.connect", lambda *args, **kwargs: new_client)
+
+    adapter.connect()
+
+    stale_client.close.assert_called_once()
+    assert adapter._client is new_client
+
+
+def test_connect_skips_reconnect_when_already_connected(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    healthy_client = _mock_client()
+    adapter = PostgresAdapter(config=TEST_POSTGRES_CONFIG)
+    adapter._client = healthy_client
+
+    connect = MagicMock()
+    monkeypatch.setattr("psycopg.connect", connect)
+
+    adapter.connect()
+
+    healthy_client.close.assert_not_called()
+    connect.assert_not_called()
+    assert adapter._client is healthy_client
+
+
+def test_fetch_one_raises_value_error_on_invalid_pk() -> None:
+    mock_client = _mock_client()
+    adapter = PostgresAdapter(config=TEST_POSTGRES_CONFIG, client=mock_client)
+
+    with pytest.raises(ValueError, match="Primary key must not be None"):
+        adapter.fetch_one(None)
+
+
+def test_fetch_one_raises_connection_error_when_not_connected() -> None:
+    adapter = PostgresAdapter(config=TEST_POSTGRES_CONFIG)
+
+    with pytest.raises(ConnectionError):
+        adapter.fetch_one("some-id")
+
+
+def test_upsert_raises_value_error_on_invalid_row() -> None:
+    mock_client = _mock_client()
+    adapter = PostgresAdapter(config=TEST_POSTGRES_CONFIG, client=mock_client)
+
+    with pytest.raises(ValueError, match="Row must be a dictionary"):
+        adapter.upsert("not-a-dict")  # type: ignore[arg-type]
+
+
+def test_upsert_raises_value_error_when_primary_key_missing() -> None:
+    mock_client = _mock_client()
+    adapter = PostgresAdapter(config=TEST_POSTGRES_CONFIG, client=mock_client)
+
+    with pytest.raises(ValueError, match="Row must include primary key column 'id'"):
+        adapter.upsert({"name": "Alice"})
+
+
+def test_upsert_raises_connection_error_when_not_connected() -> None:
+    adapter = PostgresAdapter(config=TEST_POSTGRES_CONFIG)
+
+    with pytest.raises(ConnectionError):
+        adapter.upsert({"id": "alice", "name": "Alice"})
+
+
+def test_fetch_all_raises_value_error_on_invalid_limit() -> None:
+    mock_client = _mock_client()
+    adapter = PostgresAdapter(config=TEST_POSTGRES_CONFIG, client=mock_client)
+
+    with pytest.raises(ValueError, match="Limit must be a non-negative integer"):
+        adapter.fetch_all(limit=-1)
+
+
+def test_execute_raises_value_error_on_invalid_sql() -> None:
+    mock_client = _mock_client()
+    adapter = PostgresAdapter(config=TEST_POSTGRES_CONFIG, client=mock_client)
+
+    with pytest.raises(ValueError, match="SQL must be a non-empty string"):
+        adapter.execute("")
+
+
+def test_execute_raises_value_error_on_invalid_params() -> None:
+    mock_client = _mock_client()
+    adapter = PostgresAdapter(config=TEST_POSTGRES_CONFIG, client=mock_client)
+
+    with pytest.raises(ValueError, match="Params must be a tuple"):
+        adapter.execute("SELECT 1", [])  # type: ignore[arg-type]
+
+
+def test_upsert_with_primary_key_only_uses_do_nothing() -> None:
+    mock_client = _mock_client()
+    adapter = PostgresAdapter(config=TEST_POSTGRES_CONFIG, client=mock_client)
+
+    adapter.upsert({"id": "pk-only"})
+
+    mock_cursor = mock_client.cursor.return_value.__enter__.return_value
+    insert_call = mock_cursor.execute.call_args_list[-1]
+    assert insert_call[0][1] == ("pk-only",)
+
+
+def test_execute_raises_connection_error_when_not_connected() -> None:
+    adapter = PostgresAdapter(config=TEST_POSTGRES_CONFIG)
+
+    with pytest.raises(ConnectionError):
+        adapter.execute("SELECT 1")

tests/unit/postgres_config_test.py

@@ -0,0 +1,69 @@
+"""Unit tests for PostgresConfig."""
+
+from __future__ import annotations
+
+import pytest
+
+from python_repositories.config import PostgresConfig
+
+
+def _set_required_postgres_env(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setenv("POSTGRES_URI", "postgresql://localhost/mydb")
+    monkeypatch.setenv("POSTGRES_TABLE", "users")
+
+
+def test_from_env_loads_all_fields(monkeypatch: pytest.MonkeyPatch) -> None:
+    _set_required_postgres_env(monkeypatch)
+    config = PostgresConfig.from_env(use_dotenv=False)
+    assert config.uri == "postgresql://localhost/mydb"
+    assert config.table == "users"
+    assert config.primary_key == "id"
+
+
+def test_from_env_reads_primary_key_from_env(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    _set_required_postgres_env(monkeypatch)
+    monkeypatch.setenv("POSTGRES_PRIMARY_KEY", "user_id")
+    config = PostgresConfig.from_env(use_dotenv=False)
+    assert config.primary_key == "user_id"
+
+
+def test_from_env_defaults_primary_key_to_id_when_unset(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    _set_required_postgres_env(monkeypatch)
+    monkeypatch.delenv("POSTGRES_PRIMARY_KEY", raising=False)
+    config = PostgresConfig.from_env(use_dotenv=False)
+    assert config.primary_key == "id"
+
+
+def test_from_env_raises_when_uri_missing(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.delenv("POSTGRES_URI", raising=False)
+    monkeypatch.setenv("POSTGRES_TABLE", "users")
+    with pytest.raises(Exception):
+        PostgresConfig.from_env(use_dotenv=False)
+
+
+def test_from_env_raises_when_table_missing(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setenv("POSTGRES_URI", "postgresql://localhost/mydb")
+    monkeypatch.delenv("POSTGRES_TABLE", raising=False)
+    with pytest.raises(Exception):
+        PostgresConfig.from_env(use_dotenv=False)
+
+
+def test_from_env_respects_custom_env_var_names(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    monkeypatch.setenv("CUSTOM_POSTGRES_URI", "postgresql://custom/mydb")
+    monkeypatch.setenv("CUSTOM_POSTGRES_TABLE", "items")
+    monkeypatch.setenv("CUSTOM_POSTGRES_PRIMARY_KEY", "item_id")
+    config = PostgresConfig.from_env(
+        "CUSTOM_POSTGRES_URI",
+        "CUSTOM_POSTGRES_TABLE",
+        "CUSTOM_POSTGRES_PRIMARY_KEY",
+        use_dotenv=False,
+    )
+    assert config.uri == "postgresql://custom/mydb"
+    assert config.table == "items"
+    assert config.primary_key == "item_id"

tests/unit/table_repository_interface_test.py

@@ -0,0 +1,162 @@
+"""Unit tests for TableRepositoryInterface."""
+
+from typing import Any
+
+import pytest
+
+from python_repositories.interfaces.table_repository_interface import (
+    TableRepositoryInterface,
+)
+
+
+class InMemoryTableRepo:
+    """Plain class that satisfies TableRepositoryInterface without inheritance."""
+
+    def fetch_one(self, pk: Any) -> dict[str, Any] | None:
+        return None
+
+    def fetch_all(self, *, limit: int | None = None) -> list[dict[str, Any]]:
+        del limit
+        return []
+
+    def upsert(self, row: dict[str, Any]) -> None:
+        pass
+
+    def delete(self, pk: Any) -> None:
+        pass
+
+    def execute(
+        self,
+        sql: str,
+        params: tuple[Any, ...] = (),
+    ) -> list[dict[str, Any]]:
+        del sql, params
+        return []
+
+
+def accepts_table_repo(repo: TableRepositoryInterface) -> None:
+    """Type-checking hook for TableRepositoryInterface structural subtyping."""
+    repo.fetch_one("pk")
+
+
+def test_instantiation_fails_when_fetch_one_not_implemented() -> None:
+    """Test that instantiation fails if fetch_one is not implemented."""
+
+    class Incomplete(TableRepositoryInterface):
+        def fetch_all(self, *, limit: int | None = None) -> list[dict[str, Any]]:
+            return []
+
+        def upsert(self, row: dict[str, Any]) -> None:
+            pass
+
+        def delete(self, pk: Any) -> None:
+            pass
+
+        def execute(
+            self,
+            sql: str,
+            params: tuple[Any, ...] = (),
+        ) -> list[dict[str, Any]]:
+            return []
+
+    with pytest.raises(TypeError):
+        _ = Incomplete()  # type: ignore
+
+
+def test_instantiation_fails_when_fetch_all_not_implemented() -> None:
+    """Test that instantiation fails if fetch_all is not implemented."""
+
+    class Incomplete(TableRepositoryInterface):
+        def fetch_one(self, pk: Any) -> dict[str, Any] | None:
+            return None
+
+        def upsert(self, row: dict[str, Any]) -> None:
+            pass
+
+        def delete(self, pk: Any) -> None:
+            pass
+
+        def execute(
+            self,
+            sql: str,
+            params: tuple[Any, ...] = (),
+        ) -> list[dict[str, Any]]:
+            return []
+
+    with pytest.raises(TypeError):
+        _ = Incomplete()  # type: ignore
+
+
+def test_instantiation_fails_when_upsert_not_implemented() -> None:
+    """Test that instantiation fails if upsert is not implemented."""
+
+    class Incomplete(TableRepositoryInterface):
+        def fetch_one(self, pk: Any) -> dict[str, Any] | None:
+            return None
+
+        def fetch_all(self, *, limit: int | None = None) -> list[dict[str, Any]]:
+            return []
+
+        def delete(self, pk: Any) -> None:
+            pass
+
+        def execute(
+            self,
+            sql: str,
+            params: tuple[Any, ...] = (),
+        ) -> list[dict[str, Any]]:
+            return []
+
+    with pytest.raises(TypeError):
+        _ = Incomplete()  # type: ignore
+
+
+def test_instantiation_fails_when_delete_not_implemented() -> None:
+    """Test that instantiation fails if delete is not implemented."""
+
+    class Incomplete(TableRepositoryInterface):
+        def fetch_one(self, pk: Any) -> dict[str, Any] | None:
+            return None
+
+        def fetch_all(self, *, limit: int | None = None) -> list[dict[str, Any]]:
+            return []
+
+        def upsert(self, row: dict[str, Any]) -> None:
+            pass
+
+        def execute(
+            self,
+            sql: str,
+            params: tuple[Any, ...] = (),
+        ) -> list[dict[str, Any]]:
+            return []
+
+    with pytest.raises(TypeError):
+        _ = Incomplete()  # type: ignore
+
+
+def test_instantiation_fails_when_execute_not_implemented() -> None:
+    """Test that instantiation fails if execute is not implemented."""
+
+    class Incomplete(TableRepositoryInterface):
+        def fetch_one(self, pk: Any) -> dict[str, Any] | None:
+            return None
+
+        def fetch_all(self, *, limit: int | None = None) -> list[dict[str, Any]]:
+            return []
+
+        def upsert(self, row: dict[str, Any]) -> None:
+            pass
+
+        def delete(self, pk: Any) -> None:
+            pass
+
+    with pytest.raises(TypeError):
+        _ = Incomplete()  # type: ignore
+
+
+def test_structural_subtyping() -> None:
+    """Test that a plain class satisfies TableRepositoryInterface structurally."""
+    repo: TableRepositoryInterface = InMemoryTableRepo()
+    accepts_table_repo(repo)
+    assert isinstance(repo, TableRepositoryInterface)