Add DistanceMatrix class

- the class stores the data of a distance matrix between all addresses
  + air distances
  + bicycle distances
- in addition, the "path" returned by the Google Directions API are
  also stored as a JSON serialized sequence of latitude-longitude pairs
- we assume a symmetric graph

migrations/versions/rev_20210301_16_b4dd0b8903a5_add_distance_matrix.py

@@ -0,0 +1,96 @@
+"""Add distance matrix.
+
+Revision: #b4dd0b8903a5 at 2021-03-01 16:14:06
+Revises: #8bfb928a31f8
+"""
+
+import os
+
+import sqlalchemy as sa
+from alembic import op
+from sqlalchemy.dialects import postgresql
+
+from urban_meal_delivery import configuration
+
+
+revision = 'b4dd0b8903a5'
+down_revision = '8bfb928a31f8'
+branch_labels = None
+depends_on = None
+
+
+config = configuration.make_config('testing' if os.getenv('TESTING') else 'production')
+
+
+def upgrade():
+    """Upgrade to revision b4dd0b8903a5."""
+    op.create_table(
+        'addresses_addresses',
+        sa.Column('first_address_id', sa.Integer(), nullable=False),
+        sa.Column('second_address_id', sa.Integer(), nullable=False),
+        sa.Column('city_id', sa.SmallInteger(), nullable=False),
+        sa.Column('air_distance', sa.Integer(), nullable=False),
+        sa.Column('bicycle_distance', sa.Integer(), nullable=True),
+        sa.Column('bicycle_duration', sa.Integer(), nullable=True),
+        sa.Column('directions', postgresql.JSON(), nullable=True),
+        sa.PrimaryKeyConstraint(
+            'first_address_id',
+            'second_address_id',
+            name=op.f('pk_addresses_addresses'),
+        ),
+        sa.ForeignKeyConstraint(
+            ['first_address_id', 'city_id'],
+            [
+                f'{config.CLEAN_SCHEMA}.addresses.id',
+                f'{config.CLEAN_SCHEMA}.addresses.city_id',
+            ],
+            name=op.f(
+                'fk_addresses_addresses_to_addresses_via_first_address_id_city_id',
+            ),
+            onupdate='RESTRICT',
+            ondelete='RESTRICT',
+        ),
+        sa.ForeignKeyConstraint(
+            ['second_address_id', 'city_id'],
+            [
+                f'{config.CLEAN_SCHEMA}.addresses.id',
+                f'{config.CLEAN_SCHEMA}.addresses.city_id',
+            ],
+            name=op.f(
+                'fk_addresses_addresses_to_addresses_via_second_address_id_city_id',
+            ),
+            onupdate='RESTRICT',
+            ondelete='RESTRICT',
+        ),
+        sa.UniqueConstraint(
+            'first_address_id',
+            'second_address_id',
+            name=op.f('uq_addresses_addresses_on_first_address_id_second_address_id'),
+        ),
+        sa.CheckConstraint(
+            'first_address_id < second_address_id',
+            name=op.f('ck_addresses_addresses_on_distances_are_symmetric_for_bicycles'),
+        ),
+        sa.CheckConstraint(
+            '0 <= air_distance AND air_distance < 20000',
+            name=op.f('ck_addresses_addresses_on_realistic_air_distance'),
+        ),
+        sa.CheckConstraint(
+            'bicycle_distance < 25000',
+            name=op.f('ck_addresses_addresses_on_realistic_bicycle_distance'),
+        ),
+        sa.CheckConstraint(
+            'air_distance <= bicycle_distance',
+            name=op.f('ck_addresses_addresses_on_air_distance_is_shortest'),
+        ),
+        sa.CheckConstraint(
+            '0 <= bicycle_duration AND bicycle_duration <= 3600',
+            name=op.f('ck_addresses_addresses_on_realistic_bicycle_travel_time'),
+        ),
+        schema=config.CLEAN_SCHEMA,
+    )
+
+
+def downgrade():
+    """Downgrade to revision 8bfb928a31f8."""
+    op.drop_table('addresses_addresses', schema=config.CLEAN_SCHEMA)