Comment concaténer des requêtes non liées dans SqlAlchemy

Question

Comment concaténer des requêtes sqlalchemy sans relation et sort par date?

par exemple. Ce sont les modèles:

Human 
Car 
Tree 

Et ils ont tous la colonne created. Voici les questions:

q1 = session.query(Human.created.label('created'), Human).filter(...) 
q2 = session.query(Car.created.label('created'), Car).filter(...) 
q3 = session.query(Tree.created.label('created'), Tree).filter(...) 

Maintenant, je veux concaténer ces 3 requêtes et la date order_by. Le résultat attendu serait quelque chose comme:

date  | instance 
---------------------------- 
<created> | Human<instance> 
<created> | Car<instance> 
<created> | Car<instance> 
<created> | Tree<instance> 
<created> | Human<instance> 
... 

Answer 1

Sur la base des informations fournies je geussing que vous souhaitez effectuer une union (https://www.w3schools.com/sql/sql_union.asp) sur les différentes tables.

Dans l'exemple ci-dessous, les différentes tables sont créées, une union de ces différentes tables est réalisée.

from sqlalchemy import Column, Integer, String, DateTime 
from sqlalchemy.ext.declarative import declarative_base 
from sqlalchemy import create_engine 
from sqlalchemy.orm import sessionmaker 
from datetime import datetime 

Base = declarative_base() 


class Human(Base): 
    __tablename__ = 'human' 
    id = Column('id', Integer, primary_key=True) 
    created = Column('created', DateTime) 
    name = Column('name', String(250)) 

    def __init__(self, created, name): 
     self.created = created 
     self.name = name 

    def __repr__(self): 
     return '<{created} - {name}>'.format(created=self.created, name=self.name) 


class Car(Base): 
    __tablename__ = 'car' 
    id = Column('id', Integer, primary_key=True) 
    created = Column('created', DateTime) 
    brand = Column(String(250)) 

    def __init__(self, created, brand): 
     self.created = created 
     self.brand = brand 

    def __repr__(self): 
     return '<{created} - {brand}>'.format(created=self.created, brand=self.brand) 


class Tree(Base): 
    __tablename__ = 'tree' 
    id = Column('id', Integer, primary_key=True) 
    created = Column('created', DateTime) 
    type = Column(String(250)) 

    def __init__(self, created, type): 
     self.created = created 
     self.type = type 

    def __repr__(self): 
     return '<{created} - {type}>'.format(created=self.created, type=self.type) 


engine = create_engine('sqlite:///') 
session = sessionmaker() 
session.configure(bind=engine) 
ex_ses = session() 
Base.metadata.create_all(engine) 

human = Human(datetime.now(), 'Human a') 
human2 = Human(datetime.now(), 'Human b') 
car = Car(datetime.now(), 'Car a') 
car2 = Car(datetime.now(), 'Car b') 
tree = Tree(datetime.now(), 'Tree a') 
tree2 = Tree(datetime.now(), 'Tree b') 

ex_ses.add(human) 
ex_ses.add(human2) 
ex_ses.add(car) 
ex_ses.add(car2) 
ex_ses.add(tree) 
ex_ses.add(tree2) 
ex_ses.commit() 

# Query 
h = ex_ses.query(Human.created, 'name') 
c = ex_ses.query(Car.created, 'brand') 
t = ex_ses.query(Tree.created, 'type') 

print(h.union_all(c).union_all(t).all()) 

La requête finale (dans l'instruction d'impression) retourne:

[(datetime.datetime(2017, 7, 5, 5, 55, 54, 633863), 'Human a'), 
(datetime.datetime(2017, 7, 5, 5, 55, 54, 633863), 'Human b'), 
(datetime.datetime(2017, 7, 5, 5, 55, 54, 633863), 'Car a'), 
(datetime.datetime(2017, 7, 5, 5, 55, 54, 633863), 'Car b'), 
(datetime.datetime(2017, 7, 5, 5, 55, 54, 633863), 'Tree a'), 
(datetime.datetime(2017, 7, 5, 5, 55, 54, 633863), 'Tree b')] 

Cette réponse est basée sur: How to union across multiple tables in SQLAlchemy?