我如何才能在 rxjs 的订阅中访问 c​​oncatMap 对象

Question

I use from() with pipe and concatMap and i would like to have access to the object in concatMap because i need it for doing a mapping after.

         from(objects)
          .pipe(
            concatMap(object => // i need to have access to object in subscribe
              defer(() =>
                this.service.getObjectInfors(object.id)
              )
            )
          )
          .subscribe(objectInfos => {
            if (objectInfos) {
              this.objectsTab.push(
                this.mappingObject(
                  object, // i need object in this mapping
                  objectInfos
                )
              );
            }
          });

Is it possible to do that ? Is there another way which can help me doing that ? Thanks

Answer 1

You could just pipe in a map to the inner observable inside the concatMap and send an object with both values.

Try the following

from(objects).pipe(
  concatMap(object =>
    defer(() =>
      this.service.getObjectInfors(object.id).pipe(
        map(objectInfos => ({
          obj: object,
          infos: objectInfos
        }))
      )
    )
  )
)
.subscribe((data: any) => {
  // access `data.obj` and `data.infos` here
  if (data.infos) {
    this.objectsTab.push(
      this.mappingObject(
        data.obj,
        data.infos
      )
    );
  }
});

Answer 2

If you want to avoid turning an array into a stream, you can instead merge an array of streams.

You can use the closure from array.map to map each object into the results of its stream.

const infoObjectsCalls = objects.map(object => 
  defer(() => this.service.getObjectInfors(object.id)).pipe(
    filter(objectInfos => objectInfos != null),
    map(objectInfos => ({
      object,
      objectInfos 
    }))
  )
);

merge(...infoObjectsCalls).subscribe(mappingObject =>
  this.objectsTab.push(
    this.mappingObject(mappingObject)
  )
);