Retrieve a collection of Firestore documents based on an array of unique identifiers

Question

Retrieve a collection of Firestore documents based on an array of unique identifiers

I have a Firestore collection where one of the values is an array of document IDs. My goal is to retrieve all items in the collection as well as all documents stored within the array of IDs. Here is the structure of my collection:

This is my code:

export const getFeaturedMixes = functions.https.onRequest((request, response) => {
    let result:any[] = []
    featuredMixes.get().then(mixesSnap => {

        mixesSnap.forEach(doc => {
            let docId = doc.id
            let ids = doc.data().tracks

            let resultTracks:any[] = []
            ids.forEach(id => {
                let t = tracksCollection.doc(id.track_id).get()
                resultTracks.push({'id' : id.track_id, 'data': t})
            })
            result.push({'id':docId, 'tracks': resultTracks})
        })
        return result
    })
    .then(results => {
        response.status(200).send(results)
    }).catch(function(error) {
        response.status(400).send(error)
    })
});

However, the response I receive is missing the actual document data:

{
        "id": "Xm4TJAnKcXJAuaZr",
        "tracks": [
            {
                "id": "FG3xXfldeJBbl8PY6",
                "data": {
                    "domain": {
                        "domain": null,
                        "_events": {},
                        "_eventsCount": 1,
                        "members": []
                    }
                }
            },
            {
                "id": "ONRfLIh89amSdcLt",
                "data": {
                    "domain": {
                        "domain": null,
                        "_events": {},
                        "_eventsCount": 1,
                        "members": []
                    }
                }
            }
    ]
}

The response does not contain the actual document data.

typescript firebase google-cloud-platform google-cloud-firestore google-cloud-functions

Answer 1

Answer №1

The method called get() operates asynchronously and returns a Promise. This means that you cannot immediately do something like:

 ids.forEach(id => {
      let t = tracksCollection.doc(id.track_id).get()
      resultTracks.push({'id' : id.track_id, 'data': t})
 })

You must allow the Promise returned by get() to resolve before being able to use t (which is of type DocumentSnapshot).

To handle fetching multiple documents concurrently, it's necessary to utilize Promise.all().

The following code snippet should accomplish this task. Please note that it has not been tested, and there are still sections in the code that require completion as indicated in the comments at the end. If you face any issues while finalizing it, feel free to update your question with the new code.

export const getFeaturedMixes = functions.https.onRequest((request, response) => {
    let result: any[] = []

    const docIds = [];

    featuredMixes.get()
        .then(mixesSnap => {


            mixesSnap.forEach(doc => {
                let docId = doc.id
                let ids = doc.data().tracks

                const promises = []

                ids.forEach(id => {
                    docIds.push(docId);
                    promises.push(tracksCollection.doc(id.track_id).get())
                })

            })

            return Promise.all(promises)
        })
        .then(documentSnapshotArray => {

            // Here documentSnapshotArray is an array of DocumentSnapshot corresponding to
            // the data of all the documents with track_ids

            // In addition, docIds is an array of all the ids of the FeaturedMixes document

            // IMPORTANT: These two arrays have the same length and are ordered the same way

            //I let you write the code to generate the object you want to send back to the client: loop over those two arrays in parallel and build your object


            let resultTracks: any[] = []

            documentSnapshotArray.forEach((doc, idx) => {
                // .....
                // Use the idx index to read the two Arrays in parallel

            })

            response.status(200).send(results)

        })
        .catch(function (error) {
            response.status(400).send(error)
        })
});

Answer 2

The method called get() operates asynchronously and returns a Promise. This means that you cannot immediately do something like:

 ids.forEach(id => {
      let t = tracksCollection.doc(id.track_id).get()
      resultTracks.push({'id' : id.track_id, 'data': t})
 })

You must allow the Promise returned by get() to resolve before being able to use t (which is of type DocumentSnapshot).

To handle fetching multiple documents concurrently, it's necessary to utilize Promise.all().

The following code snippet should accomplish this task. Please note that it has not been tested, and there are still sections in the code that require completion as indicated in the comments at the end. If you face any issues while finalizing it, feel free to update your question with the new code.

export const getFeaturedMixes = functions.https.onRequest((request, response) => {
    let result: any[] = []

    const docIds = [];

    featuredMixes.get()
        .then(mixesSnap => {


            mixesSnap.forEach(doc => {
                let docId = doc.id
                let ids = doc.data().tracks

                const promises = []

                ids.forEach(id => {
                    docIds.push(docId);
                    promises.push(tracksCollection.doc(id.track_id).get())
                })

            })

            return Promise.all(promises)
        })
        .then(documentSnapshotArray => {

            // Here documentSnapshotArray is an array of DocumentSnapshot corresponding to
            // the data of all the documents with track_ids

            // In addition, docIds is an array of all the ids of the FeaturedMixes document

            // IMPORTANT: These two arrays have the same length and are ordered the same way

            //I let you write the code to generate the object you want to send back to the client: loop over those two arrays in parallel and build your object


            let resultTracks: any[] = []

            documentSnapshotArray.forEach((doc, idx) => {
                // .....
                // Use the idx index to read the two Arrays in parallel

            })

            response.status(200).send(results)

        })
        .catch(function (error) {
            response.status(400).send(error)
        })
});

Answer 3

Answer №2

Appreciate the assistance, Renaud Tarnec! Your response has been incredibly valuable. The function is currently operational, but I am interested in returning a Promise.all(promises) object that contains the mix along with its tracks. Building the new object within the "then" function has proven to be challenging. Here is my finalized function:


    const mixIDs: any[] = [];
    const mixes: any[] = []

    featuredMixes.get()
        .then(mixesSnap => {
            const promises: any[] = []

            mixesSnap.forEach(doc => {
                let mixId = doc.id
                let mix = createMix(doc)
                mixes.push(mix)

                doc.data().tracks.forEach(track => {
                    let promise = tracksCollection.doc(track.track_id).get()
                    promises.push(promise)
                    mixIDs.push(mixId)
                })
            })
            return Promise.all(promises)
        })
        .then(tracksSnapshot => {

            let builtTracks = tracksSnapshot.map((doc, idx) => {
                let mId = mixIDs[idx]
                return createTrack(doc, mId)
            })

            let result = mixes.map(mix => {
                let filteredTracks = builtTracks.filter(x => x.mix_id === mix.doc_id)
                return Object.assign(mix, { 'tracks': filteredTracks })
            })
            response.status(200).send(result)
        })
        .catch(function (error) {
            response.status(400).send(error)
        })
})

Answer 4

Appreciate the assistance, Renaud Tarnec! Your response has been incredibly valuable. The function is currently operational, but I am interested in returning a Promise.all(promises) object that contains the mix along with its tracks. Building the new object within the "then" function has proven to be challenging. Here is my finalized function:


    const mixIDs: any[] = [];
    const mixes: any[] = []

    featuredMixes.get()
        .then(mixesSnap => {
            const promises: any[] = []

            mixesSnap.forEach(doc => {
                let mixId = doc.id
                let mix = createMix(doc)
                mixes.push(mix)

                doc.data().tracks.forEach(track => {
                    let promise = tracksCollection.doc(track.track_id).get()
                    promises.push(promise)
                    mixIDs.push(mixId)
                })
            })
            return Promise.all(promises)
        })
        .then(tracksSnapshot => {

            let builtTracks = tracksSnapshot.map((doc, idx) => {
                let mId = mixIDs[idx]
                return createTrack(doc, mId)
            })

            let result = mixes.map(mix => {
                let filteredTracks = builtTracks.filter(x => x.mix_id === mix.doc_id)
                return Object.assign(mix, { 'tracks': filteredTracks })
            })
            response.status(200).send(result)
        })
        .catch(function (error) {
            response.status(400).send(error)
        })
})

Retrieve a collection of Firestore documents based on an array of unique identifiers

Answer №1

Answer №2

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