refactor: improve idempotency of emby_season_id migration #109

Co-authored-by: Copilot <copilot@github.com>

Author: jessielw

backend/alembic/versions/20666951d75d_add_emby_support_and_emby_season_id_to_.py

@@ -19,16 +19,30 @@
 
 
 def upgrade() -> None:
-    # ### commands auto generated by Alembic - please adjust! ###
-    with op.batch_alter_table('seasons', schema=None) as batch_op:
-        batch_op.add_column(sa.Column('emby_season_id', sa.String(length=100), nullable=True))
+    ### commands auto generated by Alembic - please adjust! ###
+    conn = op.get_bind()
+    inspector = sa.inspect(conn)
+    existing_cols = [c['name'] for c in inspector.get_columns('seasons')]
+
+    # only add the column if it doesn't already exist (makes migration idempotent)
+    if 'emby_season_id' not in existing_cols:
+        with op.batch_alter_table('seasons', schema=None) as batch_op:
+            batch_op.add_column(
+                sa.Column('emby_season_id', sa.String(length=100), nullable=True)
+            )
 
     # ### end Alembic commands ###
 
 
 def downgrade() -> None:
-    # ### commands auto generated by Alembic - please adjust! ###
-    with op.batch_alter_table('seasons', schema=None) as batch_op:
-        batch_op.drop_column('emby_season_id')
+    ### commands auto generated by Alembic - please adjust! ###
+    conn = op.get_bind()
+    inspector = sa.inspect(conn)
+    existing_cols = [c['name'] for c in inspector.get_columns('seasons')]
+
+    # only drop the column if it exists
+    if 'emby_season_id' in existing_cols:
+        with op.batch_alter_table('seasons', schema=None) as batch_op:
+            batch_op.drop_column('emby_season_id')
 
     # ### end Alembic commands ###