Firebase response returns 200 but empty array

Question

I am currently working with Firebase and Firebase functions. I am trying to get documents within a collection (collection : 'items'). I tried doing a GET, however I only get a 200 and empty body.

app.get('/api/read/items', (req, res) => {
(async () => {
    try {
        let response = [];
        let itemRefs = db.collection('items').get().then(snapshot => {
            snapshot.forEach((item) => {
                response.push(item.data());
            });
            console.log(response);
        });
        return res.send(response);
    } catch (error) {
        debug.log(error);
        return res.status(500).send(error);
    }
})();
});

Firebase collection screenshot

Interestingly when I query a specific item, I get the JSON body with the document data included:

app.get('/api/read/:item_id', (req, res) => {
(async () => {
    try {
        const document = db.collection('items').doc(req.params.item_id);
        let item = await document.get();
        let response = item.data();
        return res.status(200).send(response);
    } catch (error) {
        console.log(error);
        return res.status(500).send(error);
    }
})();
});

Looking forward to see what mistake I made :)!

Thank you for your help!

Frank van Puffelen · Accepted Answer · 2020-05-16 21:51:06Z

2

Data is loaded form Firestore asynchronously. By the time your res.send(response) executes, the snapshot.forEach(...) hasn't been run yet.

The solution is to send the response to the client from within the innermost callback:

app.get('/api/read/items', (req, res) => {
(async () => {
    try {
        let response = [];
        return db.collection('items').get().then(snapshot => {
            snapshot.forEach((item) => {
                response.push(item.data());
            });
            console.log(response);
            return res.send(response);
        });
    } catch (error) {
        debug.log(error);
        return res.status(500).send(error);
    }
})();
});

Alternative, you can use await as you do in your second snippet:

app.get('/api/read/items', (req, res) => {
(async () => {
    try {
        let response = [];
        let snapshot = await snapshot db.collection('items').get();
        snapshot.forEach((item) => {
            response.push(item.data());
        });
        return res.send(response);
    } catch (error) {
        return res.status(500).send(error);
    }
})();
});

Which you can simplify a bit further to:

app.get('/api/read/items', (req, res) => {
(async () => {
    try {
        let snapshot = await snapshot db.collection('items').get();
        let response = snapshot.documents.map((item) => item.data());
        return res.send(response);
    } catch (error) {
        return res.status(500).send(error);
    }
})();
});

edited May 16, 2020 at 21:51

answered May 16, 2020 at 14:05

Frank van Puffelen

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3 Comments

markL12 Over a year ago

Hi Frank, Thanks for the fast response, I tried the provided code snippet, however I got the same response unfortunately.

markL12 Over a year ago

Hi Frank, Thank you for the improved code. I think I found the issue, but I am not sure I fully understand the root cause. I will add the code below.

Frank van Puffelen Over a year ago

Your answer includes the changes I proposed it seems, so I'm quite sure those contribute to it now working.

markL12 · Accepted Answer · 2020-05-17 10:27:58Z

I think I have found the root cause of the problem, which I can not explain why, due to the lack of knowledge I have with node/express. As I was testing I have my index.js file which contains :

const serviceAccount = require("./permissions.json");
const functions = require('firebase-functions');
const admin = require('firebase-admin');
const express = require('express');
const cors = require('cors');
const app = express();

const db = admin.firestore();
......
app.get('/api/read/items', (req, res) => {
    (async () => {
        try {
            let response = [];
            return db.collection('items').get().then(snapshot => {
                snapshot.forEach((item) => {
                    response.push(item.data());
                });
                console.log(response);
                return res.send(response);
            });
        } catch (error) {
            console.log(error);
            return res.status(500).send(error);
        }
    })();
});

// read item
app.get('/api/read/:item_id', (req, res) => {
    (async () => {
        try {
            const document = db.collection('items').doc(req.params.item_id);
            let item = await document.get();
            let response = item.data();
            return res.status(200).send(response);
        } catch (error) {
            console.log(error);
            return res.status(500).send(error);
        }
    })();
});


app.get('/api/read/geoFencedUsers', (req, res) => {
    (async () => {
        try {
            let response = [];
            return db.collection('geoFencedUsers').get().then(snapshot => {
                snapshot.forEach((geoFencedUser) => {
                    response.push(geoFencedUser.data());
                });
                return res.status(200).send(response);
            })
        } catch (error) {
            return res.status(500).send(error);
        }
    })();
});

Trying to do a GET call on read/geoFencedUsers return 200 but an empty response. After changing my index.js literally moving that get method above, solved the problem making all 3 calls work returning a proper response with data.:

app.get('/api/read/items', (req, res) => {
    (async () => {
        try {
            let response = [];
            return db.collection('items').get().then(snapshot => {
                snapshot.forEach((item) => {
                    response.push(item.data());
                });
                console.log(response);
                return res.send(response);
            });
        } catch (error) {
            console.log(error);
            return res.status(500).send(error);
        }
    })();
});

app.get('/api/read/geoFencedUsers', (req, res) => {
    (async () => {
        try {
            let response = [];
            return db.collection('geoFencedUsers').get().then(snapshot => {
                snapshot.forEach((geoFencedUser) => {
                    response.push(geoFencedUser.data());
                });
                return res.status(200).send(response);
            })
        } catch (error) {
            return res.status(500).send(error);
        }
    })();
});

// read item
app.get('/api/read/:item_id', (req, res) => {
    (async () => {
        try {
            const document = db.collection('items').doc(req.params.item_id);
            let item = await document.get();
            let response = item.data();
            return res.status(200).send(response);
        } catch (error) {
            console.log(error);
            return res.status(500).send(error);
        }
    })();
});

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