Firebase startAt query gives unexpected results

Question

I perform the following query:

firebase.database().ref().child('files').child('54a8924f8c417b2a281f4e3a4c639785/').orderByChild('path').startAt('54a8924f8c417b2a281f4e3a4c639785/Test Folder 2/')

And I get the following output. It's wierd that output also contains those objects which I have not queried for in the path field:

[
    {
        "fullPath": "54a8924f8c417b2a281f4e3a4c639785/Test Folder 2/Test Sub Folder/.Test Sub Folder",
        "name": "Test Sub Folder",
        "path": "54a8924f8c417b2a281f4e3a4c639785/Test Folder 2/",
        "timestamp": 1473150053359,
        "type": "dir",
        "uid": "ItvFuIIVriaHPPzeMgggwPqSlmq1",
        "$id": "-KQy_TcuUb3FsQz-CEyY",
        "$priority": null
    },
    {
        "extension": "png",
        "fullPath": "54a8924f8c417b2a281f4e3a4c639785/Test Folder 2/download.png",
        "mimeType": "image/png",
        "name": "download.png",
        "path": "54a8924f8c417b2a281f4e3a4c639785/Test Folder 2/",
        "size": 124631,
        "timestamp": 1473150091860,
        "type": "image",
        "uid": "ItvFuIIVriaHPPzeMgggwPqSlmq1",
        "$id": "-KQy_c1SLjHjTHCS1Mox",
        "$priority": null
    },
    {

        "extension": "jpg",
        "fullPath": "54a8924f8c417b2a281f4e3a4c639785/Test Folder 2/SampleImage.jpg",
        "mimeType": "image/jpeg",
        "name": "SampleImage.jpg",
        "path": "54a8924f8c417b2a281f4e3a4c639785/Test Folder 2/",
        "size": 62678,
        "timestamp": 1473150091920,
        "type": "image",
        "uid": "ItvFuIIVriaHPPzeMgggwPqSlmq1",
        "$id": "-KQy_c1WiRELh2GiZoFm",
        "$priority": null
    },
    {

        "extension": "jpg",
        "fullPath": "54a8924f8c417b2a281f4e3a4c639785/Test Folder 2/goodtimes.jpg",
        "mimeType": "image/jpeg",
        "name": "goodtimes.jpg",
        "path": "54a8924f8c417b2a281f4e3a4c639785/Test Folder 2/",
        "size": 128982,
        "timestamp": 1473150091920,
        "type": "image",
        "uid": "ItvFuIIVriaHPPzeMgggwPqSlmq1",
        "$id": "-KQy_c1_fNhcg3RKXkTj",
        "$priority": null
    },
    {

        "extension": "jpg",
        "fullPath": "54a8924f8c417b2a281f4e3a4c639785/Test Folder 2/Test Sub Folder/antibiotics2515.jpg",
        "mimeType": "image/jpeg",
        "name": "antibiotics2515.jpg",
        "path": "54a8924f8c417b2a281f4e3a4c639785/Test Folder 2/Test Sub Folder/",
        "size": 430885,
        "timestamp": 1473150091921,
        "type": "image",
        "uid": "ItvFuIIVriaHPPzeMgggwPqSlmq1",
        "$id": "-KQy_c1bzYINWTYiyFkC",
        "$priority": null
    },
    {

        "extension": "png",
        "fullPath": "54a8924f8c417b2a281f4e3a4c639785/Test Folder/download.png",
        "mimeType": "image/png",
        "name": "download.png",
        "path": "54a8924f8c417b2a281f4e3a4c639785/Test Folder/",
        "size": 124631,
        "timestamp": 1473149727313,
        "type": "image",
        "uid": "ItvFuIIVriaHPPzeMgggwPqSlmq1",
        "$id": "-KQyZDwJIbSExhaln5l-",
        "$priority": null
    },
    {

        "extension": "jpg",
        "fullPath": "54a8924f8c417b2a281f4e3a4c639785/Test Folder/SampleImage.jpg",
        "mimeType": "image/jpeg",
        "name": "SampleImage.jpg",
        "path": "54a8924f8c417b2a281f4e3a4c639785/Test Folder/",
        "size": 62678,
        "timestamp": 1473149727363,
        "type": "image",
        "uid": "ItvFuIIVriaHPPzeMgggwPqSlmq1",
        "$id": "-KQyZDwLBEIBKDx6Glq2",
        "$priority": null
    },
    {

        "extension": "jpg",
        "fullPath": "54a8924f8c417b2a281f4e3a4c639785/Test Folder/goodtimes.jpg",
        "mimeType": "image/jpeg",
        "name": "goodtimes.jpg",
        "path": "54a8924f8c417b2a281f4e3a4c639785/Test Folder/",
        "size": 128982,
        "timestamp": 1473149728493,
        "type": "image",
        "uid": "ItvFuIIVriaHPPzeMgggwPqSlmq1",
        "$id": "-KQyZDwNTejmqwN6X7ZR",
        "$priority": null
    },
    {

        "name": "Test Sub Folder",
        "path": "54a8924f8c417b2a281f4e3a4c639785/Test Folder/",
        "timestamp": 1473149760565,
        "type": "dir",
        "uid": "ItvFuIIVriaHPPzeMgggwPqSlmq1",
        "$id": "-KQyZLKsDkxlTJHDDwDX",
        "$priority": null
    },
    {

        "extension": "jpg",
        "fullPath": "54a8924f8c417b2a281f4e3a4c639785/Test Folder/Test Sub Folder/antibiotics2515.jpg",
        "mimeType": "image/jpeg",
        "name": "antibiotics2515.jpg",
        "path": "54a8924f8c417b2a281f4e3a4c639785/Test Folder/Test Sub Folder/",
        "size": 430885,
        "timestamp": 1473149889432,
        "type": "image",
        "uid": "ItvFuIIVriaHPPzeMgggwPqSlmq1",
        "$id": "-KQyZqbRe3V1BBWImBxq",
        "$priority": null
    }
]

The output also includes other results where path is "54a8924f8c417b2a281f4e3a4c639785/Test Folder/" but I queried for path starting with "54a8924f8c417b2a281f4e3a4c639785/Test Folder 2/"

Answer 1

Queries in Firebase use lexicographic ordering when sorting/filtering strings. Consequently it means that Test Folder/ is actually greater than Test Folder 2/, because / is greater than (space).

What you have to do is limiting the query with an endAt clause. Using a high Unicode code point should allow any text, as long as the prefix is the same.

.orderByChild('path')
.startAt('54a8924f8c417b2a281f4e3a4c639785/Test Folder 2/')
.endAt('54a8924f8c417b2a281f4e3a4c639785/Test Folder 2/\uf8ff')

The old Firebase documentation had a nice example for that here under Range queries, but it seems to have disappeared in the transition.