Firestore startAfter method is not working with a document as a reference

user_12533883 0
Viewed 1513

i'm having this problem where I can't make the startAfter work with my data in Firestore. I'm giving this two examples of the issue the first image is when it works, filtering with a property(createdAt), the second passing the whole doc returns empty and can't make the forEach to loop through the data

Does some know what this happen ? the documents do not have any complex information, name, creation date, all numbers for testing.

If someone had this problem, please help me with an answer, just started learning Firebase a few days ago. Thanks in advance :)

// getting the data
const response = await db
          .collection("apis")
          .orderBy("createdAt")
          .limit(3)
          .get();
        const dataSend = [];
        response.forEach((document) => {
          dataSend.push(document.data());
        });
//triggering the next data load

  const getMore = async () => {
    const limit = 3;
    const last = apis[apis.length - 1]; // last document
    console.log(last); // {name: "3", description: "3", createdAt: t, url: "3", authorId: 123123, …}

    try {
      const response = await db
        .collection("apis")
        .limit(limit)
        .orderBy("createdAt")
        .startAfter(last.createdAt) // passing createdAt to fix the problem
        .get();
      console.log(response);
      const dataSend = [];
      response.forEach((document) => {
          //this is not entering here
        dataSend.push(document.data());
      });
    } catch .....

SECOND CASE

// getting the data
const response = await db
          .collection("apis")
          .orderBy("createdAt")
          .limit(3)
          .get();
        const dataSend = [];
        response.forEach((document) => {
          dataSend.push(document.data());
        });
//triggering the next data load

  const getMore = async () => {
    const limit = 3;
    const last = apis[apis.length - 1]; // last document
    console.log(last); // {name: "3", description: "3", createdAt: t, url: "3", authorId: 123123, …}

    try {
      const response = await db
        .collection("apis")
        .limit(limit)
        .orderBy("createdAt")
        .startAfter(last) // PASSING THE WHOLE DOCUMENT AS A PARAMETER DO NOT WORK
        .get();
      console.log(response);
      const dataSend = [];
      response.forEach((document) => {
          //this is not entering here
        dataSend.push(document.data());
      });
    } catch .....
google-cloud-firestore firebase javascript
2 Answers

The solution to this problem was that I was getting the data and not the doc reference.

To fix something like this you'll have to add to the code something like this

response.docs[response.docs.length - 1]

// getting the data
const response = await db
          .collection("apis")
          .orderBy("createdAt")
          .limit(3)
          .get();
        const dataSend = [];
   const last = response.docs[response.docs.length - 1] // this is the reference to the doc that the documentations says
        response.forEach((document) => {
          dataSend.push(document.data());
        });
//triggering the next data load

  const getMore = async () => {
    const limit = 3;
    const last = response.docs[response.docs.length - 1] // last document
    console.log(last); // {name: "3", description: "3", createdAt: t, url: "3", authorId: 123123, …}

    try {
      const response = await db
        .collection("apis")
        .limit(limit)
        .orderBy("createdAt")
        .startAfter(last) //
        .get();
      console.log(response);
      const dataSend = [];
      response.forEach((document) => {
          //this is not entering here
        dataSend.push(document.data());
      });
    } catch .....

So instead of passing the last object from the database you pass the last reference to the doc before it transforms with the data() function that Firebase provides.

ALSO it works better than passing the object.createdAt.

REFERENCE

https://firebase.google.com/docs/firestore/query-data/query-cursors

user_125338830

Actually the reason that the first code block is running is because that is the correct usage of startAt().

As you can see on the examples in the Official Documentation, you should use a value in startAt() and never a full document, and that actually makes sense if you consider that you are sorting the data by a specific field and you should also start your results by a specific value on that same field.

So the correct usage is indeed .startAfter(last.createdAt) in your case.

user_128577030
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