Add Forecast model to ORM layer

- the model handles the caching of demand forecasting results
- include the database migration script

migrations/versions/rev_20210106_19_e40623e10405_add_demand_forecasting.py

@@ -0,0 +1,96 @@
+"""Add demand forecasting.
+
+Revision: #e40623e10405 at 2021-01-06 19:55:56
+Revises: #888e352d7526
+"""
+
+import os
+
+import sqlalchemy as sa
+from alembic import op
+from sqlalchemy.dialects import postgresql
+
+from urban_meal_delivery import configuration
+
+
+revision = 'e40623e10405'
+down_revision = '888e352d7526'
+branch_labels = None
+depends_on = None
+
+
+config = configuration.make_config('testing' if os.getenv('TESTING') else 'production')
+
+
+def upgrade():
+    """Upgrade to revision e40623e10405."""
+    op.create_table(
+        'forecasts',
+        sa.Column('id', sa.Integer(), autoincrement=True, nullable=False),
+        sa.Column('pixel_id', sa.Integer(), nullable=False),
+        sa.Column('start_at', sa.DateTime(), nullable=False),
+        sa.Column('time_step', sa.SmallInteger(), nullable=False),
+        sa.Column('training_horizon', sa.SmallInteger(), nullable=False),
+        sa.Column('method', sa.Unicode(length=20), nullable=False),  # noqa:WPS432
+        sa.Column('prediction', postgresql.DOUBLE_PRECISION(), nullable=False),
+        sa.PrimaryKeyConstraint('id', name=op.f('pk_forecasts')),
+        sa.ForeignKeyConstraint(
+            ['pixel_id'],
+            [f'{config.CLEAN_SCHEMA}.pixels.id'],
+            name=op.f('fk_forecasts_to_pixels_via_pixel_id'),
+            onupdate='RESTRICT',
+            ondelete='RESTRICT',
+        ),
+        sa.CheckConstraint(
+            """
+                NOT (
+                    EXTRACT(HOUR FROM start_at) < 11
+                    OR
+                    EXTRACT(HOUR FROM start_at) > 22
+                )
+            """,
+            name=op.f('ck_forecasts_on_start_at_must_be_within_operating_hours'),
+        ),
+        sa.CheckConstraint(
+            'CAST(EXTRACT(MINUTES FROM start_at) AS INTEGER) % 15 = 0',
+            name=op.f('ck_forecasts_on_start_at_minutes_must_be_quarters_of_the_hour'),
+        ),
+        sa.CheckConstraint(
+            'CAST(EXTRACT(MICROSECONDS FROM start_at) AS INTEGER) % 1000000 = 0',
+            name=op.f('ck_forecasts_on_start_at_allows_no_microseconds'),
+        ),
+        sa.CheckConstraint(
+            'EXTRACT(SECONDS FROM start_at) = 0',
+            name=op.f('ck_forecasts_on_start_at_allows_no_seconds'),
+        ),
+        sa.CheckConstraint(
+            'time_step > 0', name=op.f('ck_forecasts_on_time_step_must_be_positive'),
+        ),
+        sa.CheckConstraint(
+            'training_horizon > 0',
+            name=op.f('ck_forecasts_on_training_horizon_must_be_positive'),
+        ),
+        sa.UniqueConstraint(
+            'pixel_id',
+            'start_at',
+            'time_step',
+            'training_horizon',
+            'method',
+            name=op.f(
+                'uq_forecasts_on_pixel_id_start_at_time_step_training_horizon_method',
+            ),
+        ),
+        schema=config.CLEAN_SCHEMA,
+    )
+    op.create_index(
+        op.f('ix_forecasts_on_pixel_id'),
+        'forecasts',
+        ['pixel_id'],
+        unique=False,
+        schema=config.CLEAN_SCHEMA,
+    )
+
+
+def downgrade():
+    """Downgrade to revision 888e352d7526."""
+    op.drop_table('forecasts', schema=config.CLEAN_SCHEMA)