在Firebase查询中组合orderByChild和equalTo

Question

Given the following data structure:

{
  "comments" : {
    "-JcBbk64Gpm1SKoFHv8b" : {
      "content" : "blah",
      "createdAt" : 1417550954985,
      "link" : "http%3A%2F%2Flocalhost%3A3000%2F",
      "recommendedCount" : 0,
      "replies" : {
        "-JcBbk8gF_nQ_vjwag61" : true
      },
      "replyCount" : 1
    },
    "-JcBbk8gF_nQ_vjwag61" : {
      "content" : "blah blah",
      "createdAt" : 1417550955151,
      "link" : "http%3A%2F%2Flocalhost%3A3000%2F",
      "recommendedCount" : 0,
      "replyCount" : 1,
      "replyToComment" : "-JcBbk64Gpm1SKoFHv8b"
    }
  },
  "links" : {
    "http%3A%2F%2Flocalhost%3A3000%2F" : {
      "author" : 5,
      "commentCount" : 2,
      "comments" : {
        "-JcBbk64Gpm1SKoFHv8b" : true,
        "-JcBbk8gF_nQ_vjwag61" : true
      },
      "createdAt" : 1417550954931,
      "ratingCount" : 2,
      "recommendedCount" : 32,
      "score" : 91,
      "title" : "A Christian vs. an Atheist: Round 2",
      "url" : "http://localhost:3000/"
    }
  }
}

I would like to retrieve all the comments for a given link and sort them in reverse chronological order. I've gotten this far, but I can't figure out how to do the reverse sort because I've already used orderByChild to narrow down the results by link:

ref.orderByChild('link').equalTo(currentLink).on('value', function (snap) {
  console.log(snapshot.val());
});

If I call orderByChild() a second time like this:

ref.orderByChild('link').equalTo(currentLink).orderByChild('createdAt').on('value', function (snap) {
  console.log(snapshot.val());
});

it fails with this error message:

Uncaught Error: Query.orderByChild: You can't combine multiple orderBy calls.

I'm stumped. Any suggestions?

Answer 1

I encountered the same issues on my firebase project and I solved that like this. Please take a look.

var formRef = firebase.child('links').child(currentLink);
formRef.orderByChild('createdAt').on('value', function (snap) {
  console.log(snapshot.val());
});

It will works. Best Regards.