自动过滤SQLAlchemy查询的正确方法？

Question

我刚从sqlalchemy的CRM应用程序中反思了一个非常讨厌的架构.所有表都有一个已删除的列,我想自动过滤所有标记为已删除的实体和关系.这是我想出的:

---

class CustomizableQuery(Query):
    """An overridden sqlalchemy.orm.query.Query to filter entities

    Filters itself by BinaryExpressions
    found in :attr:`CONDITIONS`
    """

    CONDITIONS = []

    def __init__(self, mapper, session=None):
        super(CustomizableQuery, self).__init__(mapper, session)
        for cond in self.CONDITIONS:
            self._add_criterion(cond)

    def _add_criterion(self, criterion):
        criterion = self._adapt_clause(criterion, False, True)
        if self._criterion is not None:
            self._criterion = self._criterion & criterion
        else:
            self._criterion = criterion

它的使用方式如下:

class UndeletedContactQuery(CustomizableQuery):
    CONDITIONS = [contacts.c.deleted != True]

    def by_email(self, email_address):
        return EmailInfo.query.by_module_and_address('Contacts', email_address).contact

    def by_username(self, uname):
        return self.filter_by(twod_username_c=uname).one()

class Contact(object):
    query = session.query_property(UndeletedContactQuery)

Contact.query.by_email('someone@some.com')

EmailInfo是映射到电子邮件与其相关的其他模块之间的连接表的类.

这是一个映射器的示例:

contacts_map = mapper(Contact, join(contacts, contacts_cstm), {
    '_emails': dynamic_loader(EmailInfo,
                              foreign_keys=[email_join.c.bean_id],
                              primaryjoin=contacts.c.id==email_join.c.bean_id,
                              query_class=EmailInfoQuery),
    })

class EmailInfoQuery(CustomizableQuery):

    CONDITIONS = [email_join.c.deleted != True]
    # More methods here

---

这给了我想要的东西,我已经过滤掉了所有已删除的联系人.我也可以使用它作为我的映射器中dynamic_loader的query_class参数 - 但是......

1. 有没有更好的方法来做到这一点,我真的很高兴与像我这样的查询等复杂类的内部.
2. 有没有人以他们可以分享的不同方式解决这个问题？

Answer 1

您可以映射到选择.像这样:

mapper(EmailInfo, select([email_join], email_join.c.deleted == False))