Question

我几个小时以来一直在修补这个问题，而我似乎无法找到一种方法来完成这项工作。它看起来应该很简单，而且我确定它是，但我被弄糊涂了。

我有一个名为'server.py'的模块，它处理所有带瓶子的路由，这是主要的执行点。请求处理程序的一个例子就是这样，我正在概括，因为我的代码库相当沉重，而且大部分与问题无关：

server.py

@route('home')
def home():
    page = Page('home') # A template manager I made
    objects = db.get_objects(10) # This is what I can't get to work

    return page.render(objects=objects)

我希望代码从服务器端那么简单，并且使用帮助函数在db.py中完成所有数据库交互，但是我想使用仍然附加到会话的查询返回的对象，所以它必须在db.get_objects之外关闭。应该在每个请求上创建和关闭会话。我可以从home（）手动执行此操作：

server.py

@route('home')
def home():
    session = Session()
    page = Page('home') # A jinja template manager I made
    objects = db.get_objects(session, 10)

    document = page.render(objects=objects)
    session.close()

    return document

我不介意每次打开和关闭会话，这似乎是逻辑和不可避免的，无论是直接还是通过另一个对象/函数，但我不想将（手动）会话传递给每个db帮助程序功能，这对我来说似乎很麻烦。

我觉得这个问题可以通过一些OOP，会话管理器类或两者之间共享的东西来解决，但我无法弄清楚如何设计或共享它。到目前为止，我提出的最好的想法是将整个db.py包装在一个类中，让构造函数创建会话。这对辅助函数有效，但我在db.py中也有一堆其他对象也需要访问会话，如下所示，这是我的代码库中的实际对象：

db.py

class Sticker(_Base):
    __tablename__ = 'sticker'
    sticker_id = Column(Integer, ForeignKey('product.product_id'), primary_key=True)
    sticker_name = Column(String)
    svg_location = Column(String, unique=True)
    svg_width = Column(Numeric, nullable=False)
    svg_height = Column(Numeric, nullable=False)
    shaped = Column(Boolean) # Whether the cutpath countors the image

    @reconstructor
    def _get_related_properties(self, init=False):
        '''Fetches and fills out all properties that are created by the
           __init__ constructor that are not in the orm constructor.'''
        if not init:
            session = Session()
            self._product = session.query(Product).filter(Product.product_id == self.sticker_id).first()
            category_id = session.query(ProductCategory).filter(ProductCategory.product_id == self.sticker_id).first()
            session.close()

        self.sticker_id = self._product.product_id
        self.product_type = self._product.product_type
        self.date_added = self._product.date_added
        self.sticker_name = self._product.product_name

    def _get_svg_size(self):
        """Returns a tuple of the width, height of an svg"""
        # Currently only works with pixels I think. I know it fails when saved as points.
        # May want to improve this for future versions.
        # May also consider moving this function to an external util file or something.
        # Possible units: (~"em" | ~"ex" | ~"px" | ~"in" | ~"cm" | ~"mm" | ~"pt" | ~"pc")
        # Also may use viewbox attribute to determine aspect ratio and set sizes algorithmically.
        import xml.etree.ElementTree as ET
        import decimal
        # Set decimal precision
        decimal.getcontext().prec=7
        tree = ET.parse(self.svg_location)
        root = tree.getroot()

        width = None
        height = None

        width_attr = root.get('width')
        height_attr = root.get('height')

        # Get measurement units
        units = width_attr[-2:]
        if units[-1] == '%':
            units = '%'
        elif not units.isalpha():
            # if units not set assume px
            width = decimal.Decimal(width_attr)
            height = decimal.Decimal(height_attr)
            units = 'px'

        if units != 'px':
            width = decimal.Decimal(width_attr[:-2])
            height = decimal.Decimal(height_attr[:-2])
            # Convert to px if not already
            # Currently only supports in, cm, mm, and pt
            # Assumes DPI is 72
            MMPI = 2.834645669291339
            DPI = 72

            if units == 'in':
                width *= DPI
                height *= DPI
            elif units == 'pt':
                width /= DPI
                height /= DPI
            elif units == 'mm':
                width *= MMPI
                height *= MMPI
            elif units == 'cm':
                width *= MMPI * 10
                height *= MMPI * 10
            else:
                raise ValueError('Unsupported svg size unit:',units )


        return width, height

    def __init__(self, svg_location, name='', category='', metatags=[], sticker_sizes=None, active=False):
        # If no name given use filename
        if not name:
            from os.path import basename
            name = basename(svg_location).rstrip('.svg')
        # Create parent product and save to db to generate primary key/product id
        session = Session()
        self._product = Product(product_name = name, product_type = 'sticker', active = active)
        session.add(self._product)
        session.commit()
        # TODO: Handle category and metatags
        # Categories should probably be created explicitly by the admin, and so should exist
        # at the time of sticker creation. Metatags are more numerous and created on the fly
        # and so should be created automatically by the sticker constructor.

        # TODO: Expand the sticker table to reference these values from the product table maybe?
        self.sticker_id = self._product.product_id
        self.svg_location = svg_location
        self.svg_width, self.svg_height = self._get_svg_size()
        self._get_related_properties(init=True)
        # Add to the Database
        session.add(self)
        session.commit()

        # Get sticker sizes
        self.sticker_sizes = []
        # Check if a size tuple was added, default is empty
        if sticker_sizes:
            for size in sticker_sizes:
                sticker_size = StickerSize(self.sticker_id, size[0], size[1])
                session.add(sticker_size)
                self.sticker_sizes.append(StickerSize)

        session.commit()
        session.close()

大多数情况并不重要，但正如您在许多情况下所看到的，我需要从我的ORM映射对象中查询数据库，因此他们也需要访问会话。我希望这是一个简单的问题，我该怎么做？它甚至可以完成，还是我以错误的方式接近这个？如果我接近错误的话，你能提供一种有效的设计模式吗？

Answer 1

我找到了一个解决方案，即将会话附加到请求对象，这显然是每个请求都是唯一的，并且可以在模块之间共享。

我无法弄清楚如何在瓶子请求中共享会话

1 个答案: