在sqlalchemy映射集合中使用元组值

Question

在多对多关系中，我在关联表上有一些额外的数据来描述关系（数量和布尔值）。我想使用映射集合来避免直接使用关联对象，但我无法弄清楚如何使用元组来映射映射中的值。据我所知，Attribute as dict of lists using middleman table with SQLAlchemy是相似的，但倒退了。

为了说明这一点，我想做这样的事情：

>>> collection.items[item] = (3, True)
>>> collection.items[item] = (1, False)
>>> colletion.items
{"item name": (3, True), "item name": (1, False)}

这......工作......但最终SQLAlchemy尝试将元组放入数据库（我会尝试稍微重新创建）。

我也尝试在密钥中使用元组（相关对象和其他列之一），但它看起来很糟糕，和它不起作用：

>>> collection.items[item, True]  = 3
>>> collection.items[item, False] = 1
>>> collection.items
{(<item>, True): 3, (<item>, False): 1}

我可以将项目名称和一个值放在映射集合中而不会出现问题：我有另一种（结构相同）形式的这种关系，我通过建立两个关系（和关联代理）来解决这个问题。基于布尔值划分它们之间的关联表，并且它们的创建函数正确设置布尔值而没有任何进一步的干扰。不幸的是，在这种情况下，布尔值指定了一个小的语义差异（应用程序代码需要将项目视为一个组），而在当前的问题中，这是一个不可忽视的外观差异（应用程序代码不应该将项目视为组，而是值确实会改变项目的显示方式，因此也是如此。

Answer 1

链接的答案包含所有组件。 attribute_mapped_collection和association_proxy可以一起做很多事情。首先是string-＆gt; tuple（int，boolean）的字典（为m2m更新）：

from sqlalchemy import Integer, Boolean, String, Column, create_engine, \
    ForeignKey
from sqlalchemy.orm import Session, relationship
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext.associationproxy import association_proxy
from sqlalchemy.orm.collections import attribute_mapped_collection

Base = declarative_base()

class SomeClass(Base):
    __tablename__ = 'sometable'

    id = Column(Integer, primary_key=True)
    tuple_elements = relationship(
                "TupleAssociation", 
                collection_class=attribute_mapped_collection("name"),
                cascade="all, delete-orphan"
            )
    items = association_proxy("tuple_elements", "as_tuple")

class TupleAssociation(Base):
    __tablename__ = 'tuple_association'
    parent_id = Column(Integer, ForeignKey('sometable.id'), primary_key=True)
    tuple_id = Column(Integer, ForeignKey("tuple_data.id"), primary_key=True)
    name = Column(String)

    tuple_element = relationship("TupleElement")

    def __init__(self, key, tup):
        self.name = key
        self.tuple_element = TupleElement(tup)

    @property
    def as_tuple(self):
        return self.tuple_element.as_tuple

class TupleElement(Base):
    __tablename__ = 'tuple_data'

    id = Column(Integer, primary_key=True)
    col1 = Column(Integer)
    col2 = Column(Boolean)

    def __init__(self, tup):
        self.col1, self.col2 = tup

    @property
    def as_tuple(self):
        return self.col1, self.col2


e = create_engine('sqlite://')
Base.metadata.create_all(e)
s = Session(e)

collection = SomeClass()
collection.items["item name 1"] = (3, True)
collection.items["item name 2"] = (1, False)
print collection.items

s.add(collection)
s.commit()

collection = s.query(SomeClass).first()
print collection.items

这是关联上的元组和端点上的名称的另一种方式：

from sqlalchemy import Integer, Boolean, String, Column, create_engine, \
    ForeignKey
from sqlalchemy.orm import Session, relationship
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext.associationproxy import association_proxy
from sqlalchemy.orm.collections import attribute_mapped_collection

Base = declarative_base()

class SomeClass(Base):
    __tablename__ = 'sometable'

    id = Column(Integer, primary_key=True)
    tuple_elements = relationship(
                "TupleAssociation", 
                collection_class=attribute_mapped_collection("name"),
                cascade="all, delete-orphan"
            )
    items = association_proxy("tuple_elements", "as_tuple")

class TupleAssociation(Base):
    __tablename__ = 'tuple_association'
    parent_id = Column(Integer, ForeignKey('sometable.id'), primary_key=True)
    name_id = Column(Integer, ForeignKey("name_data.id"), primary_key=True)

    col1 = Column(Integer)
    col2 = Column(Boolean)

    name_element = relationship("NameElement")

    def __init__(self, key, tup):
        self.name_element = NameElement(name=key)
        self.col1, self.col2 = tup

    @property
    def name(self):
        return self.name_element.name

    @property
    def as_tuple(self):
        return self.col1, self.col2

class NameElement(Base):
    __tablename__ = 'name_data'

    id = Column(Integer, primary_key=True)
    name = Column(String)


e = create_engine('sqlite://', echo=True)
Base.metadata.create_all(e)
s = Session(e)

collection = SomeClass()
collection.items["item name 1"] = (3, True)
collection.items["item name 2"] = (1, False)
print collection.items

s.add(collection)
s.commit()

collection = s.query(SomeClass).first()
print collection.items

这可能就是你所需要的。如果你正在使用支持SQL元组的Postgresql，你可以使用hybrids plus tuple_()向上面添加更多内容，这样as_tuple也可以在SQL级别使用（下面也使用one-to - 例如，而不是关联对象）：

from sqlalchemy import Integer, Boolean, String, Column, create_engine, \
    ForeignKey
from sqlalchemy.orm import Session, relationship
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext.associationproxy import association_proxy
from sqlalchemy.orm.collections import attribute_mapped_collection
from sqlalchemy.ext import hybrid
from sqlalchemy.sql import tuple_

Base = declarative_base()

class SomeClass(Base):
    __tablename__ = 'sometable'

    id = Column(Integer, primary_key=True)
    tuple_elements = relationship(
                "TupleElement", 
                collection_class=attribute_mapped_collection("name"),
                cascade="all, delete-orphan"
            )
    items = association_proxy("tuple_elements", "as_tuple")

class TupleElement(Base):
    __tablename__ = 'tuple_data'

    id = Column(Integer, primary_key=True)
    parent_id = Column(Integer, ForeignKey('sometable.id'), nullable=False)
    name = Column(String)
    col1 = Column(Integer)
    col2 = Column(Boolean)

    def __init__(self, key, tup):
        self.name = key
        self.col1, self.col2 = tup

    @hybrid.hybrid_property
    def as_tuple(self):
        return self.col1, self.col2

    @as_tuple.expression
    def as_tuple(self):
        return tuple_(self.col1, self.col2)

e = create_engine('postgresql://scott:tiger@localhost/test', echo=True)
Base.metadata.drop_all(e)
Base.metadata.create_all(e)
s = Session(e)

collection = SomeClass()
collection.items["item name 1"] = (3, True)
collection.items["item name 2"] = (1, False)
print collection.items

s.add(collection)
s.commit()

q = s.query(SomeClass).join(SomeClass.tuple_elements)
assert q.filter(TupleElement.as_tuple == (3, True)).first() is collection
assert q.filter(TupleElement.as_tuple == (5, False)).first() is None
print s.query(TupleElement.as_tuple).all()