如果响应不为空，Angular 只运行 forkJoin？

如何解决如果响应不为空，Angular 只运行 forkJoin？

我有一个获取通知规则列表的功能。问题是，如果不存在通知规则，则该函数会崩溃。导致问题的行是 response.rules.model.map((rule) => { 返回错误：

ERROR TypeError: 无法读取未定义的属性 'map'

public getNotificationRuleItemsSet(): Observable<any[]> {
    const commonTxnList = this.configService.config.Notifications.TransactionTypeRules
        .CommonTxnList;
    const excludeTxnTypes = this.configService.config.Notifications.TransactionTypeRules
        .ExcludeTxnTypes;
    const showEffectForTxnTypes = this.configService.config.Notifications.TransactionTypeRules
        .ShowEffectForTxnTypes;

    return this.getNotificationRules().pipe(
        take(1),tap((response: any) => {
            if (response.txntypes) {
                this.txnTypes = response.txntypes.model;
            }
            if (response.accounts) {
                this.accounts = response.accounts.model;
            }
        }),switchMap((response: any) => {
            return forkJoin([
                forkJoin(
                    response.txntypes.model.map((txntype) => {
                        let commonIndex = commonTxnList.indexOf(txntype.txntypename);
                        let excludeIndex = excludeTxnTypes.indexOf(txntype.txntypename);
                        let showEffectIndex = showEffectForTxnTypes.indexOf(
                            txntype.txntypename
                        );

                        let item: INotificationTxnType = {
                            id: txntype.id,txntypename: txntype.txntypename,locname: txntype.locname,shortList: commonIndex >= 0 ? true : false,exclude: excludeIndex >= 0 ? true : false,showEffect: showEffectIndex >= 0 ? true : false,};
                        return of(item);
                    })
                ),of(response.accounts.model),forkJoin(
                    response.rules.model.map((rule) => {
                        switch (rule.type) {
                            case NotificationType.Account: {
                                return this.getoneRuleItem_Account(rule).pipe(take(1));
                            }
                            case NotificationType.TxnType: {
                                return this.getoneRuleItem_TxnType(rule).pipe(take(1));
                            }
                            case NotificationType.Currency: {
                                return this.getoneRuleItem_Currency(rule).pipe(take(1));
                            }
                            default: {
                                return of();
                            }
                        }
                    })
                ),]);
        })
    );
}

如果没有返回任何规则，则不需要运行下面的代码部分。有没有办法在这个函数中运行检查，比如if(response.rules.length > 0)然后只运行这部分代码？

forkJoin(
                    response.rules.model.map((rule) => {
                        switch (rule.type) {
                            case NotificationType.Account: {
                                return this.getoneRuleItem_Account(rule).pipe(take(1));
                            }
                            case NotificationType.TxnType: {
                                return this.getoneRuleItem_TxnType(rule).pipe(take(1));
                            }
                            case NotificationType.Currency: {
                                return this.getoneRuleItem_Currency(rule).pipe(take(1));
                            }
                            default: {
                                return of();
                            }
                        }
                    })
                ),

解决方法

您可以使用 RxJS iif 函数。此外，您可以使用 RxJS EMPTY 常量代替 of()。这样，外部 forkJoin 仍会发出，但您不会在订阅中获得 undefined。当然，如果您希望订阅中有 undefined，您可以继续使用 of()。

试试下面的方法

iif(
  () => !!response.rules && !!response.rules.model,// <-- use `forkJoin` only if `response.rules` is defined
  forkJoin(
    response.rules.model.map((rule) => {
      switch (rule.type) {
        case NotificationType.Account: {
          return this.getOneRuleItem_Account(rule).pipe(take(1));
        }
        case NotificationType.TxnType: {
          return this.getOneRuleItem_TxnType(rule).pipe(take(1));
        }
        case NotificationType.Currency: {
          return this.getOneRuleItem_Currency(rule).pipe(take(1));
        }
        default: {
          return EMPTY;
        }
      }
    })
  )
)

我已经包含了两个内部 forkJoin 的条件。

public getNotificationRuleItemsSet(): Observable <any[]> {
  ...

  return this.getNotificationRules().pipe(
    take(1),tap((response: any) => {
      if (response.txntypes) {
        this.txnTypes = response.txntypes.model;
      }
      if (response.accounts) {
        this.accounts = response.accounts.model;
      }
    }),switchMap((response: any) => {
      return forkJoin([
        iif(
          () => !!response.txntypes && !!response.txntypes.model,forkJoin(
            response.txntypes.model.map((txntype) => {
              let commonIndex = commonTxnList.indexOf(txntype.txntypename);
              let excludeIndex = excludeTxnTypes.indexOf(txntype.txntypename);
              let showEffectIndex = showEffectForTxnTypes.indexOf(
                txntype.txntypename
              );

              let item: INotificationTxnType = {
                id: txntype.id,txntypename: txntype.txntypename,locname: txntype.locname,shortList: commonIndex >= 0 ? true : false,exclude: excludeIndex >= 0 ? true : false,showEffect: showEffectIndex >= 0 ? true : false,};
              return of(item);
            })
          )
        ),of (response.accounts.model),iif(
          () => !!response.rules && !!response.rules.model,forkJoin(
            response.rules.model.map((rule) => {
              switch (rule.type) {
                case NotificationType.Account: {
                  return this.getOneRuleItem_Account(rule).pipe(take(1));
                }
                case NotificationType.TxnType: {
                  return this.getOneRuleItem_TxnType(rule).pipe(take(1));
                }
                case NotificationType.Currency: {
                  return this.getOneRuleItem_Currency(rule).pipe(take(1));
                }
                default: {
                  return EMPTY;
                }
              }
            })
          )
        ),]);
    })
  );
}