Flask, concurrent.futures и SQLAlchemy - приложение не найдено: работайте внутри функции представления или передавайте контекст приложения

Question

Я создаю приложение Flask, для которого требуется фоновый процесс, который приводит к загрузке в базу данных SQLAlchemy.

Соответствующие фрагменты:

from flask_sqlalchemy import SQLAlchemy
import concurrent.futures
import queue
from models import Upload_Tracks

app = Flask(__name__)
db.init_app(app)

app.config.update(
SQLALCHEMY_DATABASE_URI= "sqlite:///%s" % os.path.join(app.root_path, 'path/to/player.sqlite3'))

q = queue.Queue()

In database.py:

from flask_sqlalchemy import SQLAlchemy

db = SQLAlchemy()

In models.py:

def Upload_Tracks(item):
        uri = None
        title = unidecode(item['title'])
        artist = unidecode(item['artist'])
        preview = item['preview']
        energy = item['energy']
        popularity = item['popularity']
        tempo = item['tempo']
        brightness = item['brightness']
        key = item['key']
        image = item['artist_image']
        duration = item['duration']
        loudness = item['loudness']
        valence = item['valence']
        genre = item['genre']

        track = Track(title=title,
                      artist=artist,
                      uri=uri,
                      track_id=None)

        db.session.add(track)

        track.preview = preview
        track.energy = energy
        track.popularity = popularity
        track.tempo = tempo
        track.genre = genre
        track.brightness = brightness
        track.key = key
        track.image = image
        track.duration = duration
        track.loudness = loudness
        track.valence = valence

        db.session.commit()

первая функция:

# 1st background process
def build_cache():
    """
    Build general cache 
    from user's streaming
    """
    tracks_and_features = spotify.query_tracks()

    for item in tracks_and_features:
        q.put(item)

    return "CACHE BUILT"               

секунда:

def upload_cache(track):
    # save to database
    Upload_Tracks(filtered_dataset=track) 

    return "CACHE UPLOADED"               

Flask представление:

#background cache
@app.route('/cache')
def cache():
    # We can use a with statement to ensure threads are cleaned up promptly
    with concurrent.futures.ThreadPoolExecutor(max_workers=4) as executor:
        #executor.submit(build_cache)

        # start a future for a thread which sends work in through the queue
        future_to_track = {
            executor.submit(build_cache): 'TRACKER DONE'}

        while future_to_track:
            # check for status of the futures which are currently working
            done, not_done = concurrent.futures.wait(
                                                future_to_track, 
                                                timeout=0.25,
                                                return_when=concurrent.futures.FIRST_COMPLETED) 

            # if there is incoming work, start a new future
            while not q.empty():

                # fetch a track from the queue
                track = q.get()

                # Start the load operation and mark the future with its TRACK
                future_to_track[executor.submit(upload_cache, track)] = track
            # process any completed futures
            for future in done:
                track = future_to_track[future]
                try:
                    data = future.result()
                except Exception as exc:
                    print('%r generated an exception: %s' % (track, exc))
                else:
                    if track == 'TRACKER DONE':
                        print(data)
                    else:
                        print('%r track is nont uploaded to database') % (track)

                # remove the now completed future
                del future_to_track[future]


    return 'Cacheing playlist in the background...'

База данных работает нормально без потоков,Однако, когда я запускаю все это, возникает следующее исключение:

FIRST CACHE BUILT {'яркость': 0,4293608513678877, 'энергия': 0,757, 'темп': 116,494, 'продолжительность':201013, «ключ»: 5, «громкость»: -7.607, «жанр»: [u'art rock ', u'dance rock', u'folk rock ', u' mellow gold ', u'new wave',u'new wave pop ', u'power pop', u'pub rock ', u'rock', u'roots rock '],' valence ': 0.435,' artist ': u'Elvis Costello & The Attractions','популярность': 14, 'artist_image': u 'https://i.scdn.co/image/c14ffeb7855625383c266c9c04faa75516a25503',' title ': u'Poor Napoleon', 'preview': u 'https://p.scdn.co/mp3-preview/c0d57fed887ea2dbd7f69c7209adab71671b9e6e?cid=d3b2f7a12362468daa393cf457185973'} сгенерировано исключение: приложение не найдено.Либо работайте внутри функции представления, либо передавайте контекст приложения.См. http://flask -sqlalchemy.pocoo.org / contexts / .

, но, насколько мне известно, этот процесс выполняется в @app.route.как это вне контекста?как мне это исправить?

Answer 1

Сработало следующее:

def build_cache():
    with app.app_context():
        (...)

def upload_cache(track):
    with app.app_context():
        (...)

@app.route('/cache')
def cache():
    with app.app_context():
        with concurrent.futures.ThreadPoolExecutor(max_workers=4) as executor:
            (...)