Question

我正在构建一个Flask应用，该应用需要后台处理才能上传到SQLAlchemy数据库。

相关片段：

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()

在database.py中：

from flask_sqlalchemy import SQLAlchemy

db = SQLAlchemy()

在models.py中：

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()

第一个功能

：

# 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"

秒：

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

    return "CACHE UPLOADED"

Flask视图：

#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...'

数据库无需线程即可正常工作。但是，当我全部运行时，将捕获以下异常：

首次缓存建立 {'brightness'：0.4293608513678877，'energy'：0.757，'tempo'：116.494，'duration'：201013，'key'：5，'loudness'：-7.607，'genre'：[u'art rock'，u '舞蹈摇滚'，'民谣摇滚'，'柔和的黄金'，'新潮'，'新潮流行'，'力量流行'，'酒吧摇滚'，'摇滚'，u'roots摇滚”]，“价”：0.435，“艺术家”：u'Elvis Costello＆The景点'，“受欢迎程度”：14，“艺术家图像”：u'https://i.scdn.co/image/c14ffeb7855625383c266c9c04faa75516a25503'，“标题”：u'Poor Napoleon '，'preview'：u'https://p.scdn.co/mp3-preview/c0d57fed887ea2dbd7f69c7209adab71671b9e6e?cid=d3b2f7a12362468daa393cf457185973'}产生一个异常：未找到应用程序。在视图函数内部工作或推送应用程序上下文。参见http://flask-sqlalchemy.pocoo.org/contexts/。

但是据我所知，该过程正在@app.route中运行。这是如何脱离上下文的？我该如何解决？

Answer 1

万一遇到同样问题的人

from flask import current_app
def context_wrap(fn):
    app_context = current_app.app_context()
    def wrapper(*args, **kwargs):
        with app_context:
            return fn(*args, **kwargs)
    return wrapper

#Then In this case:
future_to_track = {
        executor.submit(context_wrap(build_cache)): 'TRACKER DONE'}
#OR In your case:
context_wrap(any_func_need_context)

Flask，concurrent.futures和SQLAlchemy-找不到应用程序：在视图函数中工作或推送应用程序上下文

1 个答案: