code: function list(ctx, next) {
    let cid = ctx.query.cid || '';
    let filters = ctx.state.filters || ctx.query.filters || {};
    if (cid) {
      filters.cats = cid;
    }
    ctx.state.filters = filters;
    return next();
  }
docs: 获取商品列表
  @param ctx
  @param next
  @returns {*}