fix: make migration 0002 robust with table existence checks

Migration was failing on DBs where referral_earnings or
advertising_campaign_registrations tables didn't exist yet,
causing campaign_id column to never be added. Added _has_table
and _has_column guards, wrapped backfill in existence check.

migrations/alembic/versions/0002_add_campaign_id_to_referral_earnings.py

@@ -20,42 +20,59 @@ branch_labels: Union[str, Sequence[str], None] = None
 depends_on: Union[str, Sequence[str], None] = None
 
 
-def upgrade() -> None:
-    # Add column (idempotent check)
+def _has_table(name: str) -> bool:
     conn = op.get_bind()
     inspector = sa.inspect(conn)
-    columns = [c['name'] for c in inspector.get_columns('referral_earnings')]
+    return name in inspector.get_table_names()
 
-    if 'campaign_id' not in columns:
+
+def _has_column(table: str, column: str) -> bool:
+    conn = op.get_bind()
+    inspector = sa.inspect(conn)
+    return column in [c['name'] for c in inspector.get_columns(table)]
+
+
+def upgrade() -> None:
+    # Skip if referral_earnings table doesn't exist yet
+    # (fresh DBs create it via create_all in 0001 with campaign_id already present)
+    if not _has_table('referral_earnings'):
+        return
+
+    if not _has_column('referral_earnings', 'campaign_id'):
         op.add_column('referral_earnings', sa.Column('campaign_id', sa.Integer(), nullable=True))
-        op.create_foreign_key(
-            'fk_referral_earnings_campaign_id',
-            'referral_earnings',
-            'advertising_campaigns',
-            ['campaign_id'],
-            ['id'],
-            ondelete='SET NULL',
-        )
+
+        # Only create FK if target table exists
+        if _has_table('advertising_campaigns'):
+            op.create_foreign_key(
+                'fk_referral_earnings_campaign_id',
+                'referral_earnings',
+                'advertising_campaigns',
+                ['campaign_id'],
+                ['id'],
+                ondelete='SET NULL',
+            )
+
         op.create_index('ix_referral_earnings_campaign_id', 'referral_earnings', ['campaign_id'])
 
-    # Backfill existing data — pick earliest campaign registration per user
-    # (matches runtime logic in get_user_campaign_id: ORDER BY created_at ASC LIMIT 1)
-    op.execute(
-        """
-        UPDATE referral_earnings re
-        SET campaign_id = sub.campaign_id
-        FROM (
-            SELECT DISTINCT ON (user_id) user_id, campaign_id
-            FROM advertising_campaign_registrations
-            ORDER BY user_id, created_at ASC
-        ) sub
-        WHERE sub.user_id = re.referral_id
-          AND re.campaign_id IS NULL
-        """
-    )
+    # Backfill existing data — only if source table exists
+    if _has_table('advertising_campaign_registrations') and _has_table('referral_earnings'):
+        op.execute(
+            sa.text("""
+            UPDATE referral_earnings re
+            SET campaign_id = sub.campaign_id
+            FROM (
+                SELECT DISTINCT ON (user_id) user_id, campaign_id
+                FROM advertising_campaign_registrations
+                ORDER BY user_id, created_at ASC
+            ) sub
+            WHERE sub.user_id = re.referral_id
+              AND re.campaign_id IS NULL
+            """)
+        )
 
 
 def downgrade() -> None:
-    op.drop_index('ix_referral_earnings_campaign_id', table_name='referral_earnings')
-    op.drop_constraint('fk_referral_earnings_campaign_id', 'referral_earnings', type_='foreignkey')
-    op.drop_column('referral_earnings', 'campaign_id')
+    if _has_table('referral_earnings') and _has_column('referral_earnings', 'campaign_id'):
+        op.drop_index('ix_referral_earnings_campaign_id', table_name='referral_earnings')
+        op.drop_constraint('fk_referral_earnings_campaign_id', 'referral_earnings', type_='foreignkey')
+        op.drop_column('referral_earnings', 'campaign_id')