How to write a Filter ( using DB ) with Highland.js -

-

i'm trying design workflow using highland.js. have not able figure out how highland.js can used it.

i have stream based workflow below (pseudo code),

read                      //fs.createreadstream(...)    .pipe(parse)           //jsonstream.parse(...)    .pipe(filterduplicate) //mongoclient.db.collection.count({}) > 0    .pipe(transform)       //fn(item) { return tranform(item); }    .pipe(write);          //mongoclient.db.collection.insert(doc)

the filterduplicate looks database check if read record exists (using condition) , returns boolean result. filter work, needs active db connection, want reuse till stream complete. 1 way have open connection before read , close on 'finish' event of write; means need pass connection param filter , write, work if both methods use same database.

in above workflow, filterduplicate , write may use different databases. expect connection contained , managed with-in each function, makes self-contained reusable unit.

i'm looking inputs on how can designed using highland.

thanks.

it's not going quite easy using pipe bunch of times. you've got use appropriate api method task.

here's rough example of you're going end close to:

read   .through(jsonstream.parse([true]))   .through((x) => {     h((next, push) => { // use generator async operations       h.wrapcallback( mongocountquery )( params ) // don't have way         .collect()         .tocallback((err, result) => {           if ( result > 0 ) push( err, x ); // if met criteria, hold onto           return push( null, h.nil ); // tell highland stream done         });     });   })   .merge() // because you've got stream of streams after `through`   .map(transform) // standard map through transform   .through((x) => {     h((next, push) => { // generator async operations       h.wrapcallback( mongoupdatequery )( params )         .tocallback((err, results) => {           push( err, results );           return push( null, h.nil );         });     });   })   .merge() // stream-of-streams situation   .tocallback( cb ); // call home we're done

Comments

Post a Comment

Popular posts from this blog

ios - Memory not freeing up after popping viewcontroller using ARC -

-
hi project arc based, using uinavigationcontroller make transition between viewcontroller. using profiler analyse happening behind scene memory. noticed when push viewcontroller allocate memory components , when pop not freeing allocated memory. since using arc unable implement dealloc or release component. have analysed in detail , there no memory leak in project. i not using strong property push viewcontroller. here how pushing viewcontroller. viewcontroller *obj = [[viewcontroller alloc] init]; [self.navigationcontroller pushviewcontroller:obj animated:no]; any clue whats going on? should free memory have consumed. please advise your description indicates have retain cycle, leads objects not being deallocated. typical source of retain cycles properties assigned loading nib files (usually declared iboutlet ). two strategies break them , release objects: declare property weak : @property (nonatomic, weak) iboutlet uilabel *statuslabel; set property nil in...
Read more

Django REST Framework perform_create: You cannot call `.save()` after accessing `serializer.data` -

-
i have following viewset: class artistprofileviewset(viewsets.modelviewset): queryset = artistprofile.objects.all() serializer_class = artistprofileserializer def perform_create(self, serializer): if serializer.is_valid(): serializer.save() with following serializers: class simpleartisttrackserializer(serializers.hyperlinkedmodelserializer): class meta: model = artisttrack fields = (...my fields...) class artistprofileserializer(serializers.hyperlinkedmodelserializer): owners = userserializer(many=true, required=false) tracks = simpleartisttrackserializer(many=true, required=false) class meta: model = artistprofile fields = (...my fields...) i getting following error: assertionerror: cannot call `.save()` after accessing `serializer.data`.if need access data before committing database inspect 'serializer.validated_data' instead. i don't see editing serializer.data object. th...
Read more

Why does Go error when trying to marshal this JSON? -

-
i'm trying rather simple example of trying decode json file structs using golang. however, when attempting error that json: cannot unmarshal object go value of type []main.track which don't understand. here's code in question, , json can found here . package main import ( "encoding/json" "fmt" "net/http" "os" ) // tracks group of track types type tracks struct { tracks []track } // track represents singular track type track struct { name string url string artist artist } // artist represents single artist type artist struct { name string mbid string url string } func main() { url := "http://ws.audioscrobbler.com/2.0/?method=geo.gettoptracks&api_key=c1572082105bd40d247836b5c1819623&format=json&country=netherlands" response, err := http.get(url) if err != nil { fmt.printf("%s\n", err) os.exit(1) } de...
Read more