[英]SQLAlchemy: modifying the from clause of a Query object
我有几个具有相同抽象基础和相同架构的类,它们引用数据库中的相似表。 我的查询非常简单,没有连接,简单直接的过滤条件。 我在类层次结构中使用了多态身份,因此我可以无缝地执行联合。
问题是有时我需要对几个表重复相同的查询并执行联合。 我在SQLAlchemy中找不到解决该问题的方法,并且我正在尝试在我的自定义BaseQuery类上实现一个方法,该方法可以用来克隆所有原始查询并更改用于该方法的类/映射程序,从而自动执行所有操作from子句。
例如,今天我必须做这样的事情:
query1 = MyModel1.query.filter_by(foo=bar)
query2 = MyModel2.query.filter_by(foo=bar)
query3 = MyModel3.query.filter_by(foo=bar)
query = query1.union(query2).union(query3)
我希望能够做类似的事情
query = MyModel1.query.filter_by(foo=bar).with_unions(MyModel2, MyModel3)
而且with_unions
会是这样的,其中replace_from_clause
是我追求的方法:
def with_unions(self, *others):
query = self._clone()
for other in others:
query = query.union(replace_from_clause(query, other))
return query
在SQLAlchemy的某处是否存在诸如replace_from_clause
方法之类的方法,或某种实现方法?
不用说,如果有更好的方法可以解决,我全都听着。
据我所知/根据我的经验/按照以下StackOveflow答案: https ://stackoverflow.com/a/10612690/3329834,您无法像这样与ORM结合。
我设法实现了(或多或少)您正在寻找的语法,并在返回时将所有内容重新加载到orm中。 关于联合的常规警告(相同的列数等)都在此处应用更多(需要使用相同的列名进行过滤)。 此外,我认为我不会在实践中使用它。
from functools import partial
import sqlalchemy
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import *
from sqlalchemy import orm
from sqlalchemy import sql
engine = sqlalchemy.create_engine('sqlite://')
connection = engine.connect()
Base = declarative_base()
class Student(Base):
__tablename__ = "students"
id = Column(Integer, primary_key=True)
name = Column(String(767), unique=True)
caretaker = Column(String(50))
def __repr__(self):
return 'Student(name={s.name}, caretaker={s.caretaker}'.format(s=self)
class Patient(Base):
__tablename__ = "patients"
id = Column(Integer, primary_key=True)
name = Column(String(767), unique=True)
caretaker = Column(String(50))
def __repr__(self):
return 'Patient(name={s.name}, caretaker={s.caretaker}'.format(s=self)
class StagedOperation(object):
def __init__(self, attr):
self.attr = attr
def __call__(self, *args, **kwargs):
self.args = args
self.kwargs = kwargs
class StagedQuery(object):
def __init__(self, model, session=None):
self.session = session
self.models = [model]
self.columns = [e.name for e in model.__table__.columns]
self.ops = []
def __getattr__(self, attr):
# __getattr__ fires only when an attribute is requested & not found
# We will attempt to pass on any attribute call on to the resulting
# Query objects; do note this will only work, technically and logicaly,
# with method calls, not attribute access
if hasattr(orm.query.Query, attr):
obj = StagedOperation(attr)
self.ops.append(obj)
# really getting hacky to enable "chaining"
# Could also build this into the StagedOperation.__call__
def _allow_chaining(desired_return, op, *args, **kwargs):
op(*args, **kwargs)
return desired_return
return partial(_allow_chaining, self, obj)
def with_unions(self, *models):
self.models.extend(models)
return self
def with_session(self, session):
self.session = session
return self
def query(self):
q = None
for model in self.models:
id_col = sql.literal(model.__tablename__).label('tablename')
columns = self.columns + [id_col]
mq = orm.query.Query(columns).select_from(model)
for op in self.ops:
mq = getattr(mq, op.attr)(*op.args, **op.kwargs)
q = q.union(mq) if q else mq
return q
def _deserialize_row(self, row):
ref = {e.__tablename__: e for e in self.models}
return ref[row.tablename](**{k: getattr(row, k) for k in self.columns})
def one(self):
return self._deserialize_row(
self.query().with_session(self.session).one())
def first(self):
r = self.query().with_session(self.session).first()
if r:
return self._deserialize_row(r)
def all(self):
return [
self._deserialize_row(e) for e in
self.query().with_session(self.session).all()]
if __name__ == '__main__':
engine = create_engine('sqlite://')
Session = orm.sessionmaker()
Session.configure(bind=engine)
Base.metadata.bind = engine
Base.metadata.create_all()
session = Session()
#
# Insert some objects
#
stu = Student(id=1, name='John', caretaker='Mother')
stu2 = Student(id=2, name='Sally', caretaker='Mother')
stu3 = Student(id=3, name='Scott', caretaker='Father')
pat = Patient(id=1, name='Susan', caretaker='Mother')
pat2 = Patient(id=2, name='Sally', caretaker='Father')
pat3 = Patient(id=3, name='Turnip', caretaker='Father')
session.add_all([stu, stu2, stu3, pat, pat2, pat3])
session.flush()
# Some usage options
print (
StagedQuery(Student)
.filter_by(caretaker='Mother')
.with_unions(Patient)
.with_session(session)
.all())
print (
StagedQuery(Student, session=session)
.filter_by(caretaker='Mother')
.filter_by(name='Sally')
.with_unions(Patient)
.all())
打印...
[Student(name=John, caretaker=Mother, Patient(name=Susan, caretaker=Mother, Student(name=Sally, caretaker=Mother]
[Student(name=Sally, caretaker=Mother]
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.