Make Grid.gridify() use only pickup addresses

- ensure a `Restaurant` only has one unique `Order.pickup_address`
- rework `Grid.gridify()` so that only pickup addresses are assigned
  into `Pixel`s
- include database migrations to ensure the data adhere to these
  tighter constraints

migrations/versions/rev_20210123_15_e86290e7305e_remove_orders_from_restaurants_with.py

@@ -0,0 +1,398 @@
+"""Remove orders from restaurants with invalid location ...
+
+... and also de-duplicate a couple of redundant addresses.
+
+Revision: #e86290e7305e at 2021-01-23 15:56:59
+Revises: #26711cd3f9b9
+
+1) Remove orders
+
+Some restaurants have orders to be picked up at an address that
+not their primary address. That is ok if that address is the location
+of a second franchise. However, for a small number of restaurants
+there is only exactly one order at that other address that often is
+located far away from the restaurant's primary location. It looks
+like a restaurant signed up with some invalid location that was then
+corrected into the primary one.
+
+Use the following SQL statement to obtain a list of these locations
+before this migration is run:
+
+SELECT
+    orders.pickup_address_id,
+    COUNT(*) AS n_orders,
+    MIN(placed_at) as first_order_at,
+    MAX(placed_at) as last_order_at
+FROM
+    {config.CLEAN_SCHEMA}.orders
+LEFT OUTER JOIN
+    {config.CLEAN_SCHEMA}.restaurants
+    ON orders.restaurant_id = restaurants.id
+WHERE
+    orders.pickup_address_id <> restaurants.address_id
+GROUP BY
+    pickup_address_id;
+
+50 orders with such weird pickup addresses are removed with this migration.
+
+
+2) De-duplicate addresses
+
+Five restaurants have two pickup addresses that are actually the same location.
+
+The following SQL statement shows them before this migration is run:
+
+SELECT
+    orders.restaurant_id,
+    restaurants.name,
+    restaurants.address_id AS primary_address_id,
+    addresses.id AS address_id,
+    addresses.street,
+    COUNT(*) AS n_orders
+FROM
+    {config.CLEAN_SCHEMA}.orders
+LEFT OUTER JOIN
+    {config.CLEAN_SCHEMA}.addresses ON orders.pickup_address_id = addresses.id
+LEFT OUTER JOIN
+    {config.CLEAN_SCHEMA}.restaurants ON orders.restaurant_id = restaurants.id
+WHERE
+    orders.restaurant_id IN (
+    SELECT
+        restaurant_id
+    FROM (
+        SELECT DISTINCT
+            restaurant_id,
+            pickup_address_id
+        FROM
+            {config.CLEAN_SCHEMA}.orders
+    ) AS restaurant_locations
+    GROUP BY
+        restaurant_id
+    HAVING
+        COUNT(pickup_address_id) > 1
+)
+GROUP BY
+    orders.restaurant_id,
+    restaurants.name,
+    restaurants.address_id,
+    addresses.id,
+    addresses.street
+ORDER BY
+    orders.restaurant_id,
+    restaurants.name,
+    restaurants.address_id,
+    addresses.id,
+    addresses.street;
+
+
+3) Remove addresses without any association
+
+After steps 1) and 2) some addresses are not associated with a restaurant any more.
+
+The following SQL statement lists them before this migration is run:
+
+SELECT
+    id,
+    street,
+    zip_code,
+    city
+FROM
+    {config.CLEAN_SCHEMA}.addresses
+WHERE
+    id NOT IN (
+    SELECT DISTINCT
+        pickup_address_id AS id
+    FROM
+        {config.CLEAN_SCHEMA}.orders
+    UNION
+    SELECT DISTINCT
+        delivery_address_id AS id
+    FROM
+        {config.CLEAN_SCHEMA}.orders
+    UNION
+    SELECT DISTINCT
+        address_id AS id
+    FROM
+        {config.CLEAN_SCHEMA}.restaurants
+);
+
+4) Ensure every `Restaurant` has exactly one `Address`.
+
+Replace the current `ForeignKeyConstraint` to from `Order` to `Restaurant`
+with one that also includes the `Order.pickup_address_id`.
+"""
+
+import os
+
+from alembic import op
+
+from urban_meal_delivery import configuration
+
+
+revision = 'e86290e7305e'
+down_revision = '26711cd3f9b9'
+branch_labels = None
+depends_on = None
+
+
+config = configuration.make_config('testing' if os.getenv('TESTING') else 'production')
+
+
+def upgrade():
+    """Upgrade to revision e86290e7305e."""
+    # 1) Remove orders
+    op.execute(
+        f"""
+        DELETE
+        FROM
+            {config.CLEAN_SCHEMA}.orders
+        WHERE pickup_address_id IN (
+            SELECT
+                orders.pickup_address_id
+            FROM
+                {config.CLEAN_SCHEMA}.orders
+            LEFT OUTER JOIN
+                {config.CLEAN_SCHEMA}.restaurants
+                ON orders.restaurant_id = restaurants.id
+            WHERE
+                orders.pickup_address_id <> restaurants.address_id
+            GROUP BY
+                orders.pickup_address_id
+            HAVING
+                COUNT(*) = 1
+        );
+        """,
+    )
+
+    # 2) De-duplicate addresses
+    op.execute(
+        f"""
+        UPDATE
+            {config.CLEAN_SCHEMA}.orders
+        SET
+            pickup_address_id = 353
+        WHERE
+            pickup_address_id = 548916;
+        """,
+    )
+    op.execute(
+        f"""
+        UPDATE
+            {config.CLEAN_SCHEMA}.orders
+        SET
+            pickup_address_id = 4850
+        WHERE
+            pickup_address_id = 6415;
+        """,
+    )
+    op.execute(
+        f"""
+        UPDATE
+            {config.CLEAN_SCHEMA}.orders
+        SET
+            pickup_address_id = 16227
+        WHERE
+            pickup_address_id = 44627;
+        """,
+    )
+    op.execute(
+        f"""
+        UPDATE
+            {config.CLEAN_SCHEMA}.orders
+        SET
+            pickup_address_id = 44458
+        WHERE
+            pickup_address_id = 534543;
+        """,
+    )
+    op.execute(
+        f"""
+        UPDATE
+            {config.CLEAN_SCHEMA}.orders
+        SET
+            pickup_address_id = 289997
+        WHERE
+            pickup_address_id = 309525;
+        """,
+    )
+
+    # 3) Remove addresses
+    op.execute(
+        f"""
+        DELETE
+        FROM
+            {config.CLEAN_SCHEMA}.addresses_pixels
+        WHERE
+            address_id NOT IN (
+            SELECT DISTINCT
+                pickup_address_id AS id
+            FROM
+                {config.CLEAN_SCHEMA}.orders
+            UNION
+            SELECT DISTINCT
+                delivery_address_id AS id
+            FROM
+                {config.CLEAN_SCHEMA}.orders
+            UNION
+            SELECT DISTINCT
+                address_id AS id
+            FROM
+                {config.CLEAN_SCHEMA}.restaurants
+        );
+        """,
+    )
+    op.execute(
+        f"""
+        UPDATE
+            {config.CLEAN_SCHEMA}.addresses
+        SET
+            primary_id = 302883
+        WHERE
+            primary_id = 43526;
+        """,
+    )
+    op.execute(
+        f"""
+        UPDATE
+            {config.CLEAN_SCHEMA}.addresses
+        SET
+            primary_id = 47597
+        WHERE
+            primary_id = 43728;
+        """,
+    )
+    op.execute(
+        f"""
+        UPDATE
+            {config.CLEAN_SCHEMA}.addresses
+        SET
+            primary_id = 159631
+        WHERE
+            primary_id = 43942;
+        """,
+    )
+    op.execute(
+        f"""
+        UPDATE
+            {config.CLEAN_SCHEMA}.addresses
+        SET
+            primary_id = 275651
+        WHERE
+            primary_id = 44759;
+        """,
+    )
+    op.execute(
+        f"""
+        UPDATE
+            {config.CLEAN_SCHEMA}.addresses
+        SET
+            primary_id = 156685
+        WHERE
+            primary_id = 50599;
+        """,
+    )
+    op.execute(
+        f"""
+        UPDATE
+            {config.CLEAN_SCHEMA}.addresses
+        SET
+            primary_id = 480206
+        WHERE
+            primary_id = 51774;
+        """,
+    )
+    op.execute(
+        f"""
+        DELETE
+        FROM
+            {config.CLEAN_SCHEMA}.addresses
+        WHERE
+            id NOT IN (
+            SELECT DISTINCT
+                pickup_address_id AS id
+            FROM
+                {config.CLEAN_SCHEMA}.orders
+            UNION
+            SELECT DISTINCT
+                delivery_address_id AS id
+            FROM
+                {config.CLEAN_SCHEMA}.orders
+            UNION
+            SELECT DISTINCT
+                address_id AS id
+            FROM
+                {config.CLEAN_SCHEMA}.restaurants
+        );
+        """,
+    )
+
+    # 4) Ensure every `Restaurant` has only one `Order.pickup_address`.
+    op.execute(
+        f"""
+        UPDATE
+            {config.CLEAN_SCHEMA}.orders
+        SET
+            pickup_address_id = 53733
+        WHERE
+            pickup_address_id = 54892;
+        """,
+    )
+    op.execute(
+        f"""
+        DELETE
+        FROM
+            {config.CLEAN_SCHEMA}.addresses
+        WHERE
+            id = 54892;
+        """,
+    )
+    op.create_unique_constraint(
+        'uq_restaurants_on_id_address_id',
+        'restaurants',
+        ['id', 'address_id'],
+        schema=config.CLEAN_SCHEMA,
+    )
+    op.create_foreign_key(
+        op.f('fk_orders_to_restaurants_via_restaurant_id_pickup_address_id'),
+        'orders',
+        'restaurants',
+        ['restaurant_id', 'pickup_address_id'],
+        ['id', 'address_id'],
+        source_schema=config.CLEAN_SCHEMA,
+        referent_schema=config.CLEAN_SCHEMA,
+        onupdate='RESTRICT',
+        ondelete='RESTRICT',
+    )
+    op.drop_constraint(
+        'fk_orders_to_restaurants_via_restaurant_id',
+        'orders',
+        type_='foreignkey',
+        schema=config.CLEAN_SCHEMA,
+    )
+
+
+def downgrade():
+    """Downgrade to revision 26711cd3f9b9."""
+    op.create_foreign_key(
+        op.f('fk_orders_to_restaurants_via_restaurant_id'),
+        'orders',
+        'restaurants',
+        ['restaurant_id'],
+        ['id'],
+        source_schema=config.CLEAN_SCHEMA,
+        referent_schema=config.CLEAN_SCHEMA,
+        onupdate='RESTRICT',
+        ondelete='RESTRICT',
+    )
+    op.drop_constraint(
+        'fk_orders_to_restaurants_via_restaurant_id_pickup_address_id',
+        'orders',
+        type_='foreignkey',
+        schema=config.CLEAN_SCHEMA,
+    )
+    op.drop_constraint(
+        'uq_restaurants_on_id_address_id',
+        'restaurants',
+        type_='unique',
+        schema=config.CLEAN_SCHEMA,
+    )

setup.cfg

@@ -121,6 +121,8 @@ per-file-ignores =
     migrations/versions/*.py:
         # Type annotations are not strictly enforced.
         ANN0, ANN2,
+        # Do not worry about SQL injection here.
+        S608,
         # File names of revisions are ok.
         WPS114,WPS118,
         # Revisions may have too many expressions.

src/urban_meal_delivery/console/gridify.py

@@ -8,7 +8,7 @@ from urban_meal_delivery.console import decorators
 
 
 @click.command()
-@decorators.db_revision('888e352d7526')
+@decorators.db_revision('e86290e7305e')
 def gridify() -> None:  # pragma: no cover  note:b1f68d24
     """Create grids for all cities.
 

src/urban_meal_delivery/db/addresses.py

@@ -52,7 +52,7 @@ class Address(meta.Base):
 
     # Relationships
     city = orm.relationship('City', back_populates='addresses')
-    restaurant = orm.relationship('Restaurant', back_populates='address', uselist=False)
+    restaurants = orm.relationship('Restaurant', back_populates='address')
     orders_picked_up = orm.relationship(
         'Order',
         back_populates='pickup_address',

src/urban_meal_delivery/db/grids.py

@@ -54,11 +54,12 @@ class Grid(meta.Base):
         return round((self.side_length ** 2) / 1_000_000, 1)
 
     @classmethod
-    def gridify(cls, city: db.City, side_length: int) -> db.Grid:
+    def gridify(cls, city: db.City, side_length: int) -> db.Grid:  # noqa:WPS210
         """Create a fully populated `Grid` for a `city`.
 
-        The `Grid` contains only `Pixel`s that have at least one `Address`.
+        The `Grid` contains only `Pixel`s that have at least one
-        `Address` objects outside the `city`'s viewport are discarded.
+        `Order.pickup_address`. `Address` objects outside the `.city`'s
+        viewport are discarded.
 
         Args:
             city: city for which the grid is created
@@ -72,7 +73,14 @@ class Grid(meta.Base):
         # `Pixel`s grouped by `.n_x`-`.n_y` coordinates.
         pixels = {}
 
-        for address in city.addresses:
+        pickup_addresses = (  # noqa:ECE:001
+            db.session.query(db.Address)
+            .join(db.Order, db.Address.id == db.Order.pickup_address_id)
+            .filter(db.Address.city == city)
+            .all()
+        )
+
+        for address in pickup_addresses:
             # Check if an `address` is not within the `city`'s viewport, ...
             not_within_city_viewport = (
                 address.x < 0

src/urban_meal_delivery/db/orders.py

@@ -79,12 +79,6 @@ class Order(meta.Base):  # noqa:WPS214
         sa.ForeignKeyConstraint(
             ['customer_id'], ['customers.id'], onupdate='RESTRICT', ondelete='RESTRICT',
         ),
-        sa.ForeignKeyConstraint(
-            ['restaurant_id'],
-            ['restaurants.id'],
-            onupdate='RESTRICT',
-            ondelete='RESTRICT',
-        ),
         sa.ForeignKeyConstraint(
             ['courier_id'], ['couriers.id'], onupdate='RESTRICT', ondelete='RESTRICT',
         ),
@@ -94,6 +88,14 @@ class Order(meta.Base):  # noqa:WPS214
             onupdate='RESTRICT',
             ondelete='RESTRICT',
         ),
+        sa.ForeignKeyConstraint(
+            # This foreign key ensures that there is only
+            # one `.pickup_address` per `.restaurant`
+            ['restaurant_id', 'pickup_address_id'],
+            ['restaurants.id', 'restaurants.address_id'],
+            onupdate='RESTRICT',
+            ondelete='RESTRICT',
+        ),
         sa.ForeignKeyConstraint(
             ['delivery_address_id'],
             ['addresses.id'],
@@ -302,7 +304,11 @@ class Order(meta.Base):  # noqa:WPS214
 
     # Relationships
     customer = orm.relationship('Customer', back_populates='orders')
-    restaurant = orm.relationship('Restaurant', back_populates='orders')
+    restaurant = orm.relationship(
+        'Restaurant',
+        back_populates='orders',
+        primaryjoin='Restaurant.id == Order.restaurant_id',
+    )
     courier = orm.relationship('Courier', back_populates='orders')
     pickup_address = orm.relationship(
         'Address',

src/urban_meal_delivery/db/pixels.py

@@ -12,7 +12,7 @@ class Pixel(meta.Base):
     Square pixels aggregate `Address` objects within a `City`.
     Every `Address` belongs to exactly one `Pixel` in a `Grid`.
 
-    Every `Pixel` has a unique "coordinate" within the `Grid`.
+    Every `Pixel` has a unique `n_x`-`n_y` coordinate within the `Grid`.
     """
 
     __tablename__ = 'pixels'

src/urban_meal_delivery/db/restaurants.py

@@ -34,10 +34,12 @@ class Restaurant(meta.Base):
             '0 <= estimated_prep_duration AND estimated_prep_duration <= 2400',
             name='realistic_estimated_prep_duration',
         ),
+        # Needed by a `ForeignKeyConstraint` in `Order`.
+        sa.UniqueConstraint('id', 'address_id'),
     )
 
     # Relationships
-    address = orm.relationship('Address', back_populates='restaurant')
+    address = orm.relationship('Address', back_populates='restaurants')
     orders = orm.relationship('Order', back_populates='restaurant')
 
     def __repr__(self) -> str:

tests/console/test_gridify.py

@@ -8,24 +8,31 @@ from urban_meal_delivery.console import gridify
 
 
 @pytest.mark.db
-def test_four_pixels_with_two_addresses(
+def test_two_pixels_with_two_addresses(  # noqa:WPS211
-    cli, db_session, monkeypatch, city, make_address,
+    cli, db_session, monkeypatch, city, make_address, make_restaurant, make_order,
 ):
     """Two `Address` objects in distinct `Pixel` objects.
 
     This is roughly the same test case as
-    `tests.db.test_grids.test_four_pixels_with_two_addresses`.
+    `tests.db.test_grids.test_two_pixels_with_two_addresses`.
     The difference is that the result is written to the database.
     """
     # Create two `Address` objects in distinct `Pixel`s.
-    city.addresses = [
+    # One `Address` in the lower-left `Pixel`, ...
-        # One `Address` in the lower-left `Pixel`, ...
+    address1 = make_address(latitude=48.8357377, longitude=2.2517412)
-        make_address(latitude=48.8357377, longitude=2.2517412),
+    # ... and another one in the upper-right one.
-        # ... and another one in the upper-right one.
+    address2 = make_address(latitude=48.8898312, longitude=2.4357622)
-        make_address(latitude=48.8898312, longitude=2.4357622),
-    ]
 
-    db_session.add(city)
+    # Locate a `Restaurant` at the two `Address` objects and
+    # place one `Order` for each of them so that the `Address`
+    # objects are used as `Order.pickup_address`s.
+    restaurant1 = make_restaurant(address=address1)
+    restaurant2 = make_restaurant(address=address2)
+    order1 = make_order(restaurant=restaurant1)
+    order2 = make_order(restaurant=restaurant2)
+
+    db_session.add(order1)
+    db_session.add(order2)
     db_session.commit()
 
     side_length = max(city.total_x // 2, city.total_y // 2) + 1

tests/db/test_grids.py

@@ -74,18 +74,30 @@ class TestProperties:
 class TestGridification:
     """Test the `Grid.gridify()` constructor."""
 
-    @pytest.mark.no_cover
+    @pytest.fixture
-    def test_one_pixel_without_addresses(self, city):
+    def addresses_mock(self, mocker, monkeypatch):
-        """At the very least, there must be one `Pixel` ...
+        """A `Mock` whose `.return_value` are to be set ...
 
-        ... if the `side_length` is greater than both the
+        ... to the addresses that are gridified. The addresses are
-        horizontal and vertical distances of the viewport.
+        all considered `Order.pickup_address` attributes for some orders.
+        """
+        mock = mocker.Mock()
+        query = (  # noqa:ECE001
+            mock.query.return_value.join.return_value.filter.return_value.all  # noqa:E501,WPS219
+        )
+        monkeypatch.setattr(db, 'session', mock)
+
+        return query
+
+    @pytest.mark.no_cover
+    def test_no_pixel_without_addresses(self, city, addresses_mock):
+        """Without orders, there are no `Pixel` objects on the `grid`.
 
         This test case skips the `for`-loop inside `Grid.gridify()`.
-        Interestingly, coverage.py does not see this.
         """
-        city.addresses = []
+        addresses_mock.return_value = []
 
+        # The chosen `side_length` would result in one `Pixel` if there were orders.
         # `+1` as otherwise there would be a second pixel in one direction.
         side_length = max(city.total_x, city.total_y) + 1
 
@@ -94,13 +106,13 @@ class TestGridification:
         assert isinstance(result, db.Grid)
         assert len(result.pixels) == 0  # noqa:WPS507
 
-    def test_one_pixel_with_one_address(self, city, address):
+    def test_one_pixel_with_one_address(self, city, order, addresses_mock):
         """At the very least, there must be one `Pixel` ...
 
         ... if the `side_length` is greater than both the
         horizontal and vertical distances of the viewport.
         """
-        city.addresses = [address]
+        addresses_mock.return_value = [order.pickup_address]
 
         # `+1` as otherwise there would be a second pixel in one direction.
         side_length = max(city.total_x, city.total_y) + 1
@@ -110,7 +122,7 @@ class TestGridification:
         assert isinstance(result, db.Grid)
         assert len(result.pixels) == 1
 
-    def test_one_pixel_with_two_addresses(self, city, make_address):
+    def test_one_pixel_with_two_addresses(self, city, make_order, addresses_mock):
         """At the very least, there must be one `Pixel` ...
 
         ... if the `side_length` is greater than both the
@@ -119,7 +131,8 @@ class TestGridification:
         This test case is necessary as `test_one_pixel_with_one_address`
         does not have to re-use an already created `Pixel` object internally.
         """
-        city.addresses = [make_address(), make_address()]
+        orders = [make_order(), make_order()]
+        addresses_mock.return_value = [order.pickup_address for order in orders]
 
         # `+1` as otherwise there would be a second pixel in one direction.
         side_length = max(city.total_x, city.total_y) + 1
@@ -129,12 +142,11 @@ class TestGridification:
         assert isinstance(result, db.Grid)
         assert len(result.pixels) == 1
 
-    def test_one_pixel_with_address_too_far_south(self, city, address):
+    def test_no_pixel_with_one_address_too_far_south(self, city, order, addresses_mock):
         """An `address` outside the `city`'s viewport is discarded."""
         # Move the `address` just below `city.southwest`.
-        address.latitude = city.southwest.latitude - 0.1
+        order.pickup_address.latitude = city.southwest.latitude - 0.1
-
+        addresses_mock.return_value = [order.pickup_address]
-        city.addresses = [address]
 
         # `+1` as otherwise there would be a second pixel in one direction.
         side_length = max(city.total_x, city.total_y) + 1
@@ -145,16 +157,15 @@ class TestGridification:
         assert len(result.pixels) == 0  # noqa:WPS507
 
     @pytest.mark.no_cover
-    def test_one_pixel_with_address_too_far_west(self, city, address):
+    def test_no_pixel_with_one_address_too_far_west(self, city, order, addresses_mock):
         """An `address` outside the `city`'s viewport is discarded.
 
-        This test is a logical sibling to `test_one_pixel_with_address_too_far_south`
+        This test is a logical sibling to
-        and therefore redundant.
+        `test_no_pixel_with_one_address_too_far_south` and therefore redundant.
         """
         # Move the `address` just left to `city.southwest`.
-        address.longitude = city.southwest.longitude - 0.1
+        order.pickup_address.longitude = city.southwest.longitude - 0.1
-
+        addresses_mock.return_value = [order.pickup_address]
-        city.addresses = [address]
 
         # `+1` as otherwise there would be a second pixel in one direction.
         side_length = max(city.total_x, city.total_y) + 1
@@ -165,13 +176,13 @@ class TestGridification:
         assert len(result.pixels) == 0  # noqa:WPS507
 
     @pytest.mark.no_cover
-    def test_four_pixels_with_two_addresses(self, city, make_address):
+    def test_two_pixels_with_two_addresses(self, city, make_address, addresses_mock):
         """Two `Address` objects in distinct `Pixel` objects.
 
         This test is more of a sanity check.
         """
         # Create two `Address` objects in distinct `Pixel`s.
-        city.addresses = [
+        addresses_mock.return_value = [
             # One `Address` in the lower-left `Pixel`, ...
             make_address(latitude=48.8357377, longitude=2.2517412),
             # ... and another one in the upper-right one.
@@ -194,7 +205,9 @@ class TestGridification:
     @pytest.mark.db
     @pytest.mark.no_cover
     @pytest.mark.parametrize('side_length', [250, 500, 1_000, 2_000, 4_000, 8_000])
-    def test_make_random_grids(self, db_session, city, make_address, side_length):
+    def test_make_random_grids(  # noqa:WPS211
+        self, db_session, city, make_address, make_restaurant, make_order, side_length,
+    ):
         """With 100 random `Address` objects, a grid must have ...
 
         ... between 1 and a deterministic upper bound of `Pixel` objects.
@@ -202,7 +215,10 @@ class TestGridification:
         This test creates confidence that the created `Grid`
         objects adhere to the database constraints.
         """
-        city.addresses = [make_address() for _ in range(100)]
+        addresses = [make_address() for _ in range(100)]
+        restaurants = [make_restaurant(address=address) for address in addresses]
+        orders = [make_order(restaurant=restaurant) for restaurant in restaurants]
+        db_session.add_all(orders)
 
         n_pixels_x = (city.total_x // side_length) + 1
         n_pixels_y = (city.total_y // side_length) + 1

tests/forecasts/timify/test_aggregate_orders.py

@@ -17,16 +17,34 @@ class TestAggregateOrders:
     """
 
     @pytest.fixture
-    def one_pixel_grid(self, db_session, city, restaurant):
+    def addresses_mock(self, mocker, monkeypatch):
+        """A `Mock` whose `.return_value` are to be set ...
+
+        ... to the addresses that are gridified. The addresses are
+        all considered `Order.pickup_address` attributes for some orders.
+
+        Note: This fixture also exists in `tests.db.test_grids`.
+        """
+        mock = mocker.Mock()
+        query = (  # noqa:ECE001
+            mock.query.return_value.join.return_value.filter.return_value.all  # noqa:E501,WPS219
+        )
+        monkeypatch.setattr(db, 'session', mock)
+
+        return query
+
+    @pytest.fixture
+    def one_pixel_grid(self, db_session, city, restaurant, addresses_mock):
         """A persisted `Grid` with one `Pixel`.
 
-        `restaurant` must be a dependency as otherwise
+        `restaurant` must be a dependency as otherwise the `restaurant.address`
-        its `.address` is not put into the database.
+        is not put into the database as an `Order.pickup_address`.
         """
+        addresses_mock.return_value = [restaurant.address]
+
         # `+1` as otherwise there would be a second pixel in one direction.
         side_length = max(city.total_x, city.total_y) + 1
         grid = db.Grid.gridify(city=city, side_length=side_length)
-
         db_session.add(grid)
 
         assert len(grid.pixels) == 1  # sanity check
@@ -272,17 +290,17 @@ class TestAggregateOrders:
         assert result['total_orders'].sum() == 18
 
     @pytest.fixture
-    def two_pixel_grid(self, db_session, city, make_address, make_restaurant):
+    def two_pixel_grid(  # noqa:WPS211
-        """A persisted `Grid` with two `Pixel` objects.
+        self, db_session, city, make_address, make_restaurant, addresses_mock,
-
+    ):
-        `restaurant` must be a dependency as otherwise
+        """A persisted `Grid` with two `Pixel` objects."""
-        its `.address` is not put into the database.
-        """
         # One `Address` in the lower-left `Pixel`, ...
         address1 = make_address(latitude=48.8357377, longitude=2.2517412)
         # ... and another one in the upper-right one.
         address2 = make_address(latitude=48.8898312, longitude=2.4357622)
 
+        addresses_mock.return_value = [address1, address2]
+
         # Create `Restaurant`s at the two addresses.
         make_restaurant(address=address1)
         make_restaurant(address=address2)
@@ -307,7 +325,8 @@ class TestAggregateOrders:
         In total, there are 30 orders.
         """
         address1, address2 = two_pixel_grid.city.addresses
-        restaurant1, restaurant2 = address1.restaurant, address2.restaurant
+        # Rarely, an `Address` may have several `Restaurant`s in the real dataset.
+        restaurant1, restaurant2 = address1.restaurants[0], address2.restaurants[0]
 
         # Create one order every other hour for `restaurant1`.
         for hour in range(11, 23, 2):