Firestore - How to get document id after adding a document to a collection

Question

Is there a way to acquire the document id that was generated after adding a document to a collection?

If I add a document to a collection that represents a \"post\"

Answer 1

As others mentioned also, we can get the document reference once it added. After we get the document reference on the behalf of id, we can update the same

Service.ts file

async funName(data: Data){
      let docRef = this.firestore.collection('table-name').add(data);
      console.log(docRef)
      try {
        const docAdded = await docRef;
        console.log(docAdded.id);
        this.firestore.doc('table-name/' + docAdded.id).update({ id: docAdded.id });
        return docRef;
      }
      catch (err) {
        return err;
      }
    }

component.ts file

async addData(){
    try{
      let res =  await this.dataServ.funName(this.form.value);
      this.snackbar.open('success', 'Success');
    }catch(ex){
      this.disabled = false;
      this.snackbar.open('err', 'Error')
      console.log(ex, 'exception');
    }
  }

Answer 2

If you want to use async/await instead of .then(), you can write it like this:

const post = async (doc) => {
    const doc_ref = await db.collection(my_collection).add(doc)
    return doc_ref.id
}

If you want to catch any errors in this function, include .catch():

    const doc_ref = await db.collection(my_collection).add(doc).catch(err => { ... })

or you can have the calling function catch the error.

Answer 3

For Android, Java, you're suppose to get the Document ID before you set() or add() something to Firestore. Like so:

//Fields: 
CollectionReference toolsCollectionRef = FirebaseFirestore.getInstance().collection(toolsCollection);
CustomPOJO_Model toolToPost; 

//In Methods: 
String newDocID= toolsCollectionRef.document().getId();   //Get Doc ID first. 
toolToPost.setToolID(newDocID);

//Now use the doc ID:
toolsCollectionRef.document(newDocID).set(toolToPost.getConvertedTool_KeyValuePair ()).addOnCompleteListener(new OnCompleteListener<Void>() {
    @Override
    public void onComplete(@NonNull Task<Void> task) {
    }
});

//Re-use same ID in another post: 
usersCollectionRef.document(mAuth.getUid()).collection(usersToolsCollection).document(toolToPost.getToolID()).set(toolToPost.getConvertedTool_KeyValuePair()); 

Answer 4

Here's what I do, as mentioned in your question. Not sure if it is best practice, but it works for easy access.

When creating the document in the first place

firebase.firestore().collection("cities").doc().set({ name: Tokyo,
country: Japan })

you can set the id of the doc and put that exact id in it as a property:

firebase.firestore().collection("cities").doc('id-generated-from-somewhere')
.set({ id: 'id-generated-from-somewhere', name: Tokyo, country: Japan })

Answer 5

If using promises, I'd recommend using fat arrow function as it opens up the possibility for using this.foo even in the .then function

db.collection("cities").add({
    name: "Tokyo",
    country: "Japan"
})
.then(docRef => {
    console.log("Document written with ID: ", docRef.id);
    console.log("You can now also access this. as expected: ", this.foo)
})
.catch(error => console.error("Error adding document: ", error))

Using function(docRef) means you cannot access this.foo, and error will be thrown

.then(function(docRef) {
    console.log("Document written with ID: ", docRef.id);
    console.log("You can now NOT access this. as expected: ", this.foo)
})

While fat arrow functions will allow you to access this.foo as expected

.then(docRef => {
    console.log("Document written with ID: ", docRef.id);
    console.log("You can now also access this. as expected: ", this.foo)
})

---

Edit/addition 2020:

A more popular way these days may be to use async/await instead. Notice that you have to add async in front of the function declaration:

async function addCity(newCity) {
  const newCityAdded = await db.collection("cities").add(newCity)
  console.log("the new city:", newCityAdded)
  console.log("it's id:", newCityAdded.id)
}

And if you only want the id it can be grabbed using descructuring. Destructuring allows you to grab any key/value-pair in the response:

async function addCity(newCity) {
  const { id } = await db.collection("cities").add(newCity)
  console.log("the new city's id:", id)
}

It's also possible to use destructuring to grab the value and rename to whatever you want:

async function addCity(newCity) {
  const { id: newCityId } = await db.collection("cities").add(newCity)
  console.log("the new city's id:", newCityId)
}

Answer 6

Yes it is possible. When you call the .add method on a collection, a DocumentReference object is returned. DocumentReference has the id field, so you can get the id after the document was created.

// Add a new document with a generated id.
db.collection("cities").add({
    name: "Tokyo",
    country: "Japan"
})
.then(function(docRef) {
    console.log("Document written with ID: ", docRef.id);
})
.catch(function(error) {
    console.error("Error adding document: ", error);
});

This example is in JavaScript. Visit the documentation for other languages.