从数据库条目获取应用程序配置

Question

我正在寻找一种方法来从数据库条目中设置一些静态应用程序配置值（作为werkzeug服务器端口）。我的应用程序使用SQLAlchemy和蓝图，并且目前从对象（config.py）获取配置。

假设数据库的配置仍然来自配置文件，如何从数据库配置应用程序的其余部分？

Answer 1

从表中读取键/值项并从这些项中设置配置。请记住，值列只能有一种类型（我在这里用String去掉了）。解决此问题的一种方法是创建具有不同值类型的多态表，但这超出了此答案的范围。我通过明确命名应该是不同类型的键来解决它。

import os 
from flask import Flask 
from flask_sqlalchemy import SQLAlchemy 

app = Flask(__name__) 

# assuming the database is an sqlite file "app.db" in the instance folder 
app.config['SQLALCHEMY_DATABASE_URI'] = os.path.join(app.instance_path, 'app.db') 
db = SQLAlchemy() 
db.init_app(app) 


class ConfigItem(db.Model): 
    """Represents one config item. 

    All values are strings, so non-string values must be converted later. 

    :param key: config key 
    :param value: configured value 
    """ 

    __tablename__ = 'config_item' 

    key = db.Column(db.String, primary_key=True) 
    value = db.Column(db.String) 

    def __str__(self): 
     return '{}: {}'.format(self.key, self.value) 

    def __repr__(self): 
     return 'ConfigItem(key={!r}, value={!r})'.format(self.key, self.value) 


# map a converter function to key names, so that values will be converted from strings to the correct type 
# this is just the mapper for Flask config keys, the list will be much longer will extension config keys added 
config_types = { 
    lambda value: value == 'True': ('DEBUG', 'PROPAGATE_EXCEPTIONS', 'PRESERVE_CONTEXT_ON_EXCEPTION', 'SESSION_COOKIE_HTTPONLY', 'SESSION_COOKIE_SECURE', 'USE_X_SENDFILE', 'TRAP_HTTP_EXCEPTIONS', 'TRAP_BAD_REQUEST_ERRORS', 'JSON_AS_ASCII', 'JSON_SORT_KEYS', 'JSONIFY_PRETTYPRINT_REGULAR'), 
    int: ('PERMANENT_SESSION_LIFETIME', 'MAX_CONTENT_LENGTH', 'SEND_FILE_MAX_AGE_DEFAULT') 
} 
# convert the type to key list mapping above to a key to type mapping 
config_types = {key: type for type, keys in config_types.items() for key in keys} 

# flask_sqlalchemy database connections only work in an app context 
# we're not in a request handler, so have to create the context explicitly 
with app.app_context(): 
    for item in ConfigItem.query: 
     # set the config value for each key, converting it if it's not a string 
     if item.key in config_types: 
      app.config[item.key] = config_types[item.key](value) 
     else: 
      app.config[item.key.upper()] = item.value