"""
为 users 表增加 preferred_language 字段（用户首选语言 zh/en）
"""

from alembic import op
import sqlalchemy as sa


def upgrade():
    op.add_column(
        "users",
        sa.Column(
            "preferred_language",
            sa.String(length=8),
            nullable=True,
            comment="首选语言（zh/en）",
        ),
    )


def downgrade():
    op.drop_column("users", "preferred_language")