Is it possible to get an array of unique values in firebase?

Question

Consider the following data stored in Firebase:

{
  "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"
    }
  }
}

Is it possible to build a query for Firebase to return an array of the unique values of one of the child nodes. For example to return ["IPA", "Pale Wheat"]

Answer 1

Nope, you cannot query a collection for unique values of a specific property of each item. You can filter on such values, so ref.child('beers').orderByChild('type').equalTo('IPA'). But that's not what you were asking. :-)

Typically if you want this type of operation in Firebase (or most other NoSQL databases), you'll keep the items (or references to the items) under a group:

{
  "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"
      },
    }
  }
}

Of course that only works if you want to only keep them in one category. If you want multiple categories, you can store references to each item under multiple categories:

{
  "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
    }
  }
}