在另一个 Observable 中订阅一个 observable

Question

我正在调试我的代码，该代码从数据库中获取UserWallets，然后通过连接外部 REST API 为它们生成地址。现在我有一个嵌套在另一个订阅中的订阅，但我读到这是一个糟糕的解决方案（它实际上不起作用，我认为这就是原因）。

userWalletDao.getUnregisteredUserWallets()
                .subscribe(nextWallet -> {
                    log.info("Fetched next wallet for registration {}", nextWallet);
                    blockchainIntegration.registerUserWallet(nextWallet.getUserId())
                            .subscribe(address -> {
                                nextWallet.setAddress(address);
                                userWalletDao.persistUserWalletAddress(nextWallet);
                                log.info("Registered wallet {} with address {}.", nextWallet, address);
                            });
                });

我试图在一次订阅中进行，但如果我将钱包平面映射到地址，我会丢失一个 UserWallet 对象来为其设置一个获取的地址并将其保存回数据库中。

如何获取钱包，然后调用 API 为它生成一个地址？

getUnregisteredUserWallets() 返回Observable<UserWallet> 和registerUserWallet() 返回Single<String>。

Answer 1

强烈建议阅读和理解第一条评论中提到的依赖子流。

您可以通过将可观察序列更改为类似的方式来解决您的问题

       userWalletDao.getUnregisteredUserWallets()
                .flatMap(nextWallet -> registerUserWallet(nextWallet.getUserId()).toObservable()
                        .flatMap(address -> Observable.fromCallable(() -> new Pair<>(nextWallet, address))))  // return both wallet from previous mapping and address from current mapping to the next level
                .flatMapCompletable(walletAddressPair -> Completable.fromAction(()->{
                    Wallet nextWallet = walletAddressPair.first;
                    String address = walletAddressPair.second;
                    nextWallet.setAddress(address);
                    userWalletDao.persistUserWalletAddress(nextWallet);
                    log.info("Registered wallet {} with address {}.", nextWallet, address);
                    // here wallet and address have been saved to db. This operation is a completable action, you don't have to return any result 
                    // from it and forward to the next level.  Thats why flatMapCompletable is used.
                }))
                .subscribeWith(new DisposableCompletableObserver() {
                    @Override
                    public void onComplete() {
                       // All actions completed
                    }

                    @Override
                    public void onError(Throwable e) {
                      // any error occurred in the observable chain
                    }
                });