1

所以，我在 Postgres 中有这个嵌套的集合表，这里是 schema 和 data。我在我的 Express 应用程序下面有这个控制器功能代码，以使用 Knex 和一些承诺处理将嵌套类别作为数组获取：

const getCategories = (req, res, db) => {
  const products = []

  db.raw(`
    SELECT child.id, child.name, child.path
    FROM product_category parent
    JOIN product_category child
    ON child.lower BETWEEN parent.lower AND parent.upper
    WHERE parent.id = 1
      AND
        (
          SELECT COUNT(*)
          FROM product_category node
          WHERE child.lower BETWEEN node.lower AND node.upper
            AND node.lower BETWEEN parent.lower AND parent.upper
        ) = 2 
  `)
  .then(categories => {
    if (categories.rows.length) {
      const categoryPromises = categories.rows.map(category => {
        return db.raw(`
          SELECT child.id, child.name, child.path
          FROM product_category parent
          JOIN product_category child
          ON child.lower BETWEEN parent.lower AND parent.upper
          WHERE parent.id = ${category.id}
          AND
            (
              SELECT COUNT(*)
              FROM product_category node
              WHERE child.lower BETWEEN node.lower AND node.upper
                AND node.lower BETWEEN parent.lower AND parent.upper
            ) = 2 
        `)
        .then(subcategories => {
          const categoryObject = { ...category, subcategories: [] }
          if (subcategories.rows.length) {
            subcategories.rows.map(subcategory => {
              categoryObject.subcategories.push(subcategory)
            })
            products.push(categoryObject)
          } else {
            res.status(400).json("No subcategories")
          }
        })
      })

      return Promise.all(categoryPromises)
      .then(() => res.json(products))

    } else {
      res.status(400).json("No categories")
    }
  })
}

我得到响应没有问题，但是数组内第一级对象的顺序并不一致。有时是这样的：

[
  {
    "id": 9,
    "name": "Other Products",
    "path": "other_products",
    "subcategories": [
      {
        "id": 10,
        "name": "Slides",
        "path": "slides"
      },
      {
        "id": 11,
        "name": "Buoys",
        "path": "buoys"
      }
    ]
  },
  {
    "id": 2,
    "name": "Boats",
    "path": "boats",
    "subcategories": [
      {
        "id": 3,
        "name": "Rescue Boats",
        "path": "rescue_boats"
      },
      {
        "id": 4,
        "name": "Dive Boats",
        "path": "dive_boats"
      },
      {
        "id": 5,
        "name": "Tamarans",
        "path": "tamarans"
      },
      {
        "id": 6,
        "name": "Dragon Boats",
        "path": "dragon_boats"
      },
      {
        "id": 7,
        "name": "Kayaks",
        "path": "kayaks"
      },
      {
        "id": 8,
        "name": "Speedboats",
        "path": "speedboats"
      }
    ]
  }
]

或者像这样：

[
  {
    "id": 2,
    "name": "Boats",
    "path": "boats",
    "subcategories": [
      {
        "id": 3,
        "name": "Rescue Boats",
        "path": "rescue_boats"
      },
      {
        "id": 4,
        "name": "Dive Boats",
        "path": "dive_boats"
      },
      {
        "id": 5,
        "name": "Tamarans",
        "path": "tamarans"
      },
      {
        "id": 6,
        "name": "Dragon Boats",
        "path": "dragon_boats"
      },
      {
        "id": 7,
        "name": "Kayaks",
        "path": "kayaks"
      },
      {
        "id": 8,
        "name": "Speedboats",
        "path": "speedboats"
      }
    ]
  },
  {
    "id": 9,
    "name": "Other Products",
    "path": "other_products",
    "subcategories": [
      {
        "id": 10,
        "name": "Slides",
        "path": "slides"
      },
      {
        "id": 11,
        "name": "Buoys",
        "path": "buoys"
      }
    ]
  }
]

我如何使它保持一致？也许这有点微不足道，但一段时间后它变得有点烦人。提前致谢！

4

1 回答 1

0

我还在r /learnprogramming subreddit 中要求增加它得到回答的机会。用户u/shhh-quiet给出了一个很好的解决方案。

基本上，这是因为我在我的代码片段上写了错误的代码。我将引用他的全部答案：

我认为您正在从嵌套查询的承诺链内部构建 products 数组。根据查询需要多长时间，产品最终会得到不同的排序。

在使用 Promise 时，这通常被认为是不好的。它基本上打破了您使用 map 和 Promise.all 建立的顺序。

你应该改变：

products.push(categoryObject)

...至：

return categoryObject

并改变：

return Promise.all(categoryPromises)
  .then(() => res.json(products))

...至：

return Promise.all(categoryPromises)
  .then(products => res.json(products))

并删除：

const products = []

编辑：为了清楚起见，他没有 StackOverflow 帐户，他允许我发布他的答案。

于 2019-03-18T15:34:27.827 回答