是否可以在 firebase 中获取一组唯一值？

Question

考虑以下存储在 Firebase 中的数据：

{
  "beers": {
    "-jwhkclclmecl": {
      "name": "Two Hearted Ale",
      "type": "IPA",
      "brewery": "Bells"
    },
    "-ckqjheh292od": {
      "name": "Dirty Blonde Ale",
      "type": "Pale Wheat",
      "brewery": "Atwater"
    },
    "-hcwiu3cp902d": {
      "name": "Diabolical",
      "type": "IPA",
      "brewery": "North Peak"
    }
  }
}

是否可以为 Firebase 构建查询以返回其中一个子节点的唯一值的数组。例如返回["IPA", "Pale Wheat"]

Answer 1

不，您不能在集合中查询每个项目的特定属性的唯一值。您可以过滤此类值，因此ref.child('beers').orderByChild('type').equalTo('IPA'). 但这不是你要问的。:-)

通常，如果您希望在 Firebase（或大多数其他 NoSQL 数据库）中执行此类操作，您会将项目（或项目的引用）保留在一个组下：

{
  "beer_types": {
    "IPA": {
      "-jwhkclclmecl": {
        "name": "Two Hearted Ale",
        "brewery": "Bells"
      },
      "-hcwiu3cp902d": {
        "name": "Diabolical",
        "brewery": "North Peak"
      }
    },
    "Pale Wheat": {
      "-ckqjheh292od": {
        "name": "Dirty Blonde Ale",
        "brewery": "Atwater"
      },
    }
  }
}

当然，这仅在您只想将它​​们保留在一个类别中时才有效。如果您想要多个类别，您可以将每个项目的引用存储在多个类别下：

{
  "beers": {
    "-jwhkclclmecl": {
      "name": "Two Hearted Ale",
      "type": "IPA",
      "brewery": "Bells"
    },
    "-ckqjheh292od": {
      "name": "Dirty Blonde Ale",
      "type": "Pale Wheat",
      "brewery": "Atwater"
    },
    "-hcwiu3cp902d": {
      "name": "Diabolical",
      "type": "IPA",
      "brewery": "North Peak"
    }
  }
  "beer_types": {
    "IPA": {
      "-jwhkclclmecl": true,
      "-hcwiu3cp902d": true
    },
    "Pale Wheat": {
      "-ckqjheh292od": true
    }
  },
  "breweries": {
    "Bells": {
      "-jwhkclclmecl": true
    },
    "Atwater": {
      "-ckqjheh292od": true
    }
    "North Peak": {
      "-hcwiu3cp902d": true
    }
  }
}