Friebase: How to join multiple tables and send the json with API

Question

Here is my data structure of firebase realtime db.
I want to make an API to send toolboxes data in node.js.

And here is the code I made.

router.get('/toolboxes', function(req, res, next) {
  // toolboxes
  toolboxesRef.orderByChild('timestamp').once('value', snapshot => {
    var toolboxes = [];
    snapshot.forEach(childSnapshot => {
      // get toolbox
      var toolbox = {};
      toolbox = childSnapshot.val();
      // add toolbox to toolboxes
      toolboxes.unshift(toolbox);
    })
    res.send(toolboxes);
  })
});

The response now doesn't fit my expectation.
User in toolbox doesn't join the the user table with the u_id.

What I expect is like :

[
    {
        "createdTime": {
            "datetime": "2020/02/23 12:14",
            "timestamp": 1582388083410,
            "fromNow": "a minute ago"
        },
        "description": "Test2",
        "id": "-M0hfUcS6L3wxCnqd2MK",
        "name": "Test2",
        "tags": [
            "網路產業",
            "專案經理",
            "google"
        ],
        "tools": [
            "slack",
            "gitlab",
            "gmail",
            "adobe-after-effect"
        ],
        "user": {
            "avatar": {
                "height": 50,
                "is_silhouette": false,
                "url": "https://platform-lookaside.fbsbx.com/platform/profilepic/?asid=2993082880704327&height=50&width=50&ext=1584979302&hash=AeQoVqr0x0UwYXuI",
                "width": 50
            },
            "createdTime": {
                "datetime": "2020/02/23 12:01",
                "timestamp": 1582387303217
            },
            "id": "2993082880704327",
            "link": {
                "facebook": "https://www.facebook.com/app_scoped_user_id/YXNpZADpBWEZAiRS1rMHRoMlEwTGJpQmdGWkxxYjFQakxGZAzhsLTRRbnZALUXJ6ZAnN3Rm43MW9VZAnE0NmFJWjZA0ckVsYVpNYkhZAdVJEYkxYU3pUZAEJHT1JISmp1b3YwVE1yaF85cFRmSVRyMzM0QjZANTzcycndD/"
            },
            "name": {
                "firstName": "Chung Ping",
                "fullName": "Tseng Chung Ping",
                "lastName": "Tseng"
            },
            "toolboxes": {
                "-M0hcYsndNhnbx695UAF": {
                    "value": "-M0hcYsndNhnbx695UAF"
                },
                "-M0hfUcS6L3wxCnqd2MK": {
                    "value": "-M0hfUcS6L3wxCnqd2MK"
                }
            }
        },
        "ownerStatus": true
    },
    {
        "createdTime": {
            "datetime": "2020/02/23 12:01",
            "timestamp": 1582387314574,
            "fromNow": "14 minutes ago"
        },
        "description": "Test",
        "id": "-M0hcYsndNhnbx695UAF",
        "name": "Test",
        "tags": [
            "網路產業",
            "專案經理",
            "google"
        ],
        "tools": [
            "slack",
            "gitlab",
            "gmail"
        ],
        "user": {
            "avatar": {
                "height": 50,
                "is_silhouette": false,
                "url": "https://platform-lookaside.fbsbx.com/platform/profilepic/?asid=2993082880704327&height=50&width=50&ext=1584979302&hash=AeQoVqr0x0UwYXuI",
                "width": 50
            },
            "createdTime": {
                "datetime": "2020/02/23 12:01",
                "timestamp": 1582387303217
            },
            "id": "2993082880704327",
            "link": {
                "facebook": "https://www.facebook.com/app_scoped_user_id/YXNpZADpBWEZAiRS1rMHRoMlEwTGJpQmdGWkxxYjFQakxGZAzhsLTRRbnZALUXJ6ZAnN3Rm43MW9VZAnE0NmFJWjZA0ckVsYVpNYkhZAdVJEYkxYU3pUZAEJHT1JISmp1b3YwVE1yaF85cFRmSVRyMzM0QjZANTzcycndD/"
            },
            "name": {
                "firstName": "Chung Ping",
                "fullName": "Tseng Chung Ping",
                "lastName": "Tseng"
            },
            "toolboxes": {
                "-M0hcYsndNhnbx695UAF": {
                    "value": "-M0hcYsndNhnbx695UAF"
                },
                "-M0hfUcS6L3wxCnqd2MK": {
                    "value": "-M0hfUcS6L3wxCnqd2MK"
                }
            }
        },
        "ownerStatus": true
    }
]

What should I optimize my code if I want to get each toolboxes data but also join the other tables like users and tools etc. Thanks a lot.