如何通过返回布尔值的 Observable 的函数过滤作为数组的 Observable

Question

Say I have an observable called selectedUsers$ that returns an Observable that is an array in the following format.

[
 {
   'userId': 'someId',
   'other': 'properties',
   'that': 'dont',
   'matter': '.',
 },
 {
   'userId': 'anotherId',
   'other': 'properties',
   'that': 'dont',
   'matter': '.',
 },
 {
   'userId': 'yetAnotherId',
   'other': 'properties',
   'that': 'dont',
   'matter': '.',
 },
];  

I want to filter this array based on if the user is an administrator or not for a module and only collect the ones that are not administrators. To get if the user is an administrator for a module, a call has to be made to another function that takes the moduleName and userId value and returns true or false as an Observable.

The signature for the function is

isUserAdministratorForModule$(moduleName: string, userId: string): Observable<boolean>  

The function I want to create is

getNonAdministratorUsersForModule$(moduleName: string): Observable<IUser[]> {
   return this.selectedUsers$.map(selectedUsers => selectedUsers.map(user => 
          user.id)
         .filter(userId => !this.userService.isUserAdministratorForModule$(moduleName, userId))
}  

That's what I have come up with. It is wrong but I have written it so you get a better idea. The problem is the filter is an array method and the function inside of it returns an Observable of boolean.

Any ideas on how to filter an Observable that returns an array and the passed in function in the filter returns an Observable of true or false based on a value on an object in the array?

Thanks

Answer 1

Looks like you're using RxJS 5.0 in your snippets, but here's a possible solution with RxJS 6.0.

You should be able to retrofit this.

Aspects to point out:

• switchMap() accepts the most recent collection of users returned
• Having to invoke isUserAdministratorForModule for each user means you end up with Observable<boolean>[]
• Using of(user) with forkJoin() associates each user with their isUserAdministratorForModule result
• The merge() then collects each user-result value observable back into a single stream
• Finally, the combination of filter() and map() weeds out the users of interest

 const { forkJoin, merge, of } = rxjs; const { filter, map, switchMap } = rxjs.operators; const selectedUsers = [ { 'userId': 'someId', 'other': 'properties', 'that': 'dont', 'matter': '.', }, { 'userId': 'anotherId', 'other': 'properties', 'that': 'dont', 'matter': '.', }, { 'userId': 'yetAnotherId', 'other': 'properties', 'that': 'dont', 'matter': '.', }, ]; function isUserAdministratorForModule(moduleName, userId) { return of(userId === 'someId'); } function getNonAdministratorUsersForModule(moduleName) { return of(selectedUsers).pipe( switchMap(users => merge(...users.map(user => forkJoin( of(user), isUserAdministratorForModule(moduleName, user.userId)) ), ), ), filter(([user, isAdmin]) => !isAdmin), map(([user, isAdmin]) => user), ); } getNonAdministratorUsersForModule().subscribe(console.log);

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