SQLAlchemy与Postgresql ARRAY的关系

Question

假设我们有一个带有两个表A,B的PostgreSQL数据库.

table A columns: id, name
table B columns: id, name, array_a

array_a表B中的列包含表A中的可变长度的数组.在SQLAlchemy中,我们有两个类来模拟这些表,比如A类和B类.

以下工作正常,以获取对象B中引用的所有对象A:

session.query(A).join(B, A.id == func.any(B.array_a)).filter(B.id == <id>).all()

我们如何在B中创建一个引用与数组对应的对象A的关系？尝试使用func.any上面的列比较器,但它抱怨ANY(array_a)不是模型中的列.如上所述指定primaryjoin条件似乎也没有削减它.

Answer 1

这种反模式被称为"Jaywalking" ; 和PostgreSQL强大的类型系统使它非常诱人.你应该使用另一张桌子:

CREATE TABLE table_a (
    id SERIAL PRIMARY KEY,
    name VARCHAR
);

CREATE TABLE table_b (
    id SERIAL PRIMARY KEY,
    name VARCHAR
);

CREATE TABLE a_b (
    a_id INTEGER PRIMARY KEY REFERENCES table_a(id),
    b_id INTEGER PRIMARY KEY REFERENCES table_b(id)
)

哪个映射:

from sqlalchemy import *
from sqlalchemy.dialects import postgresql
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import *

Base = declarative_base()

a_b_table = Table("a_b", Base.metadata,
    Column("a_id", Integer, ForeignKey("table_a.id"), primary_key=True),
    Column("b_id", Integer, ForeignKey("table_b.id"), primary_key=True))

class A(Base):
    __tablename__ = "table_a"
    id = Column(Integer, primary_key=True)
    name = Column(String)

class B(Base):
    __tablename__ = "table_b"
    id = Column(Integer, primary_key=True)
    name = Column(String)
    a_set = relationship(A, secondary=a_b_table, backref="b_set")

例:

>>> print Query(A).filter(A.b_set.any(B.name == "foo"))
SELECT table_a.id AS table_a_id, table_a.name AS table_a_name 
FROM table_a 
WHERE EXISTS (SELECT 1 
FROM a_b, table_b 
WHERE table_a.id = a_b.a_id AND table_b.id = a_b.b_id AND table_b.name = :name_1)

如果你坚持使用该ARRAY列,最好的办法是使用一个"看起来"像一个正确的关联表的备用选择.

from sqlalchemy import *
from sqlalchemy.dialects import postgresql
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import *

Base = declarative_base()


class A(Base):
    __tablename__ = "table_a"
    id = Column(Integer, primary_key=True)
    name = Column(String)

class B(Base):
    __tablename__ = "table_b"
    id = Column(Integer, primary_key=True)
    name = Column(String)
    array_a = Column(postgresql.ARRAY(Integer))

a_b_selectable = select([func.unnest(B.array_a).label("a_id"),
                         B.id.label("b_id")]).alias()

A.b_set = relationship(B, secondary=a_b_selectable,
                          primaryjoin=A.id == a_b_selectable.c.a_id,
                          secondaryjoin=a_b_selectable.c.b_id == B.id,
                          viewonly=True,)

B.a_set = relationship(A, secondary=a_b_selectable,
                          primaryjoin=A.id == a_b_selectable.c.a_id,
                          secondaryjoin=a_b_selectable.c.b_id == B.id,
                          viewonly=True)

这给你:

>>> print Query(A).filter(A.b_set.any(B.name == "foo"))
SELECT table_a.id AS table_a_id, table_a.name AS table_a_name 
FROM table_a 
WHERE EXISTS (SELECT 1 
FROM (SELECT unnest(table_b.array_a) AS a_id, table_b.id AS b_id 
FROM table_b) AS anon_1, table_b 
WHERE table_a.id = anon_1.a_id AND anon_1.b_id = table_b.id AND table_b.name = :name_1)

很明显,因为那里没有真正的桌子,所以viewonly=True如果你避免了jaywalking,你就无法得到漂亮,动态的客观善良.

Answer 2

或者您可以像下面这样显式加入：

class A(Base):
    __tablename__ = "table_a"
    id = Column(Integer, primary_key=True)
    name = Column(String)

class B(Base):
    __tablename__ = "table_b"
    id = Column(Integer, primary_key=True)
    name = Column(String)
    array_a = Column(postgresql.ARRAY(Integer))

    a_ids= relationship('A',primaryjoin='A.id == any_(foreign(B.array_a))',uselist=True)