java - 非常简单的 Firestore 交易失败

Question

我正在为一项 super 简单的交易而苦苦挣扎。它总是失败并显示消息“事务失败所有重试”，但是 logcat 上没有错误消息。

当我调试它时，我看到它被重试了好几次。我真的不知道为什么，因为其他事务运行没有问题。

我只想将一个文档从一个集合克隆到另一个集合。从“videos”到“favorites”(我知道这可以在交易之外完成，正如@Alex 指出的那样，但这只是失败的部分，真正的交易时间更长)

private void copy(
    final DocumentReference SOURCEDOCREF, 
    final CollectionReference TARGETCOLREF) {

        Transaction.Function<? extends Void> transaction = new Transaction.Function<Void>() {

            @Nullable
            @Override
            public Void apply(@NonNull Transaction transaction) throws FirebaseFirestoreException {

                DocumentSnapshot doc = transaction.get(SOURCEDOCREF);
                if (doc.exists()) {
                    DocumentReference favoriteRef = TARGETCOLREF.document("FV_" + doc.getId());
                    Map<String, Object> data = doc.getData();
                    transaction.set(favoriteRef, data);
                    return null;

                    // NOTE: This is reached, ie. the source doc exists
                    // the data recovered, and set into the transaction.
                } else
                    throw new FirebaseFirestoreException("Item does not exist", FirebaseFirestoreException.Code.NOT_FOUND);
            }
        };

        setMode(MODE_SPLASH);
        FirebaseFirestore.getInstance().runTransaction(transaction)
                .addOnSuccessListener(
                        (Activity) getContext(),
                        new OnSuccessListener<Object>() {
                            @Override
                            public void onSuccess(Object aVoid) {
                                setMode(MODE_FOLLOW);
                            }
                        })
                .addOnFailureListener(new OnFailureListener() {
                    @Override
                    public void onFailure(@NonNull Exception e) {
                        hide();
                        DialogHelper.customToast(getContext(), e.getMessage());
                    }
                });
    }

Answer 1

根据documentation about transactions :

If a transaction reads documents and another client modifies any of those documents, Cloud Firestore retries the transaction. This feature ensures that the transaction runs on up-to-date and consistent data.

因此，如果源文档在事务完成之前已被修改，您可以预期您的事务将被重试。

您也可以预期交易会失败。

A transaction can fail for the following reasons:

• The transaction contains read operations after write operations. Read operations must always come before any write operations.
• The transaction read a document that was modified outside of the transaction. In this case, the transaction automatically runs again. The transaction is retried a finite number of times.

A failed transaction returns an error and does not write anything to the database. You do not need to roll back the transaction; Cloud Firestore does this automatically.