feat: Region-datasets join table and simulation year

alembic/versions/20260303_886921687770_region_datasets_join_table_and_.py

@@ -0,0 +1,66 @@
+"""region_datasets_join_table_and_simulation_year
+
+Revision ID: 886921687770
+Revises: 963e91da9298
+Create Date: 2026-03-03 18:56:13.551288
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision: str = '886921687770'
+down_revision: Union[str, Sequence[str], None] = '963e91da9298'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Upgrade schema."""
+    # Create the region_datasets join table
+    op.create_table('region_datasets',
+    sa.Column('region_id', sa.Uuid(), nullable=False),
+    sa.Column('dataset_id', sa.Uuid(), nullable=False),
+    sa.ForeignKeyConstraint(['dataset_id'], ['datasets.id'], ),
+    sa.ForeignKeyConstraint(['region_id'], ['regions.id'], ),
+    sa.PrimaryKeyConstraint('region_id', 'dataset_id')
+    )
+
+    # Migrate existing region->dataset links into the join table
+    op.execute("""
+        INSERT INTO region_datasets (region_id, dataset_id)
+        SELECT id, dataset_id FROM regions
+        WHERE dataset_id IS NOT NULL
+    """)
+
+    # Drop the old FK and column from regions
+    op.drop_constraint(op.f('regions_dataset_id_fkey'), 'regions', type_='foreignkey')
+    op.drop_column('regions', 'dataset_id')
+
+    # Add year column to simulations
+    op.add_column('simulations', sa.Column('year', sa.Integer(), nullable=True))
+
+
+def downgrade() -> None:
+    """Downgrade schema."""
+    op.drop_column('simulations', 'year')
+    op.add_column('regions', sa.Column('dataset_id', sa.UUID(), autoincrement=False, nullable=True))
+
+    # Migrate join table data back to the FK column (pick one dataset per region)
+    op.execute("""
+        UPDATE regions r
+        SET dataset_id = rd.dataset_id
+        FROM (
+            SELECT DISTINCT ON (region_id) region_id, dataset_id
+            FROM region_datasets
+            ORDER BY region_id
+        ) rd
+        WHERE r.id = rd.region_id
+    """)
+
+    op.alter_column('regions', 'dataset_id', nullable=False)
+    op.create_foreign_key(op.f('regions_dataset_id_fkey'), 'regions', 'datasets', ['dataset_id'], ['id'])
+    op.drop_table('region_datasets')