Wie Sie Spalten mit verknüpften anonymous aliased Tabellen in SqlAlchemy angeben

Question

Ich habe Probleme herauszufinden, die richtige Syntax zu verwenden, um Spalten bei der Abfrage verknüpften Tabellen, die anonym Aliasing mit SqlAlchemy generative Syntax richtig anzugeben.

Das Schema hat zwei Tabellen, one-to-many:

user = Table('user', meta, 
    Column('id', Integer, primary_key=True, autoincrement = False), 
    Column('name', String), 
    Column('department_id', Integer, ForeignKey('department.id')) 
) 

department = Table('department', meta, 
    Column('id', Integer, primary_key=True, autoincrement = True), 
    Column('name', String) 
) 

Eine einzelne Tabelle Abfrage funktioniert:

# alias the tables anonymously 
u = user.alias() 
d = department.alias() 

# single table select works 
q = select([ 
    u.c.id.label('UserId'), 
    u.c.name.label('User'), 
    ]) 
r = conn.execute(q).fetchall() 
log.debug(r[0].keys()) 
# [u'UserId', u'User'] 

Aber wenn die aliased Tabellen verknüpft werden, sind sie umbenannt, und ich weiß nicht, was die neuen Namen sein werden, also kann ich die Spalten nicht spezifizieren:

# join the 2 aliased tables 
from_ = u.join(d) 
log.debug(from_.c.keys()) 
# [u'%(172847020 user)s_id', u'%(172847020 user)s_name', u'%(172847020 user)s_department_id', u'%(172846668 department)s_id', u'%(172846668 department)s_name'] 

# this does not work 
q = select([ 
    from_.c.user_id.label('UserId'), 
    from_.c.user_name.label('User'), 
    from_.c.department_name.label('Department'), 
    ]) 
r = conn.execute(q).fetchall() 
log.debug(r[0].keys()) 

Wie kann ich das zum Funktionieren bringen?

Dies ist die komplette Testcode:

import logging 
from sqlalchemy import create_engine, Table, Column, Integer, String, MetaData, ForeignKey 
from sqlalchemy.sql import * 

log = logging.getLogger('generative_test') 
logging.basicConfig(level=logging.DEBUG, 
     format='%(asctime)s,%(msecs)03d %(levelname)s [%(filename)s.%(funcName)s @ %(lineno)d.%(thread)d] %(message)s') 

engine = create_engine('sqlite:///:memory:', echo = False, echo_pool = False) 
meta = MetaData() 
meta.bind = engine 

user = Table('user', meta, 
    Column('id', Integer, primary_key=True, autoincrement = False), 
    Column('name', String), 
    Column('department_id', Integer, ForeignKey('department.id')) 
) 

department = Table('department', meta, 
    Column('id', Integer, primary_key=True, autoincrement = True), 
    Column('name', String) 
) 

meta.create_all(engine) 
conn = engine.connect() 

conn.execute(department.insert(),[ 
    {'name':'bosses'}, 
    {'name':'peons'}, 
]) 
conn.execute(user.insert(),[ 
    {'name':'Mr. Slate','department_id':1}, 
    {'name': 'Fred','department_id':2}, 
    {'name': 'Barney','department_id':2}, 
]) 

# alias the tables anonymously 
u = user.alias() 
d = department.alias() 

# single table select works 
q = select([ 
    u.c.id.label('UserId'), 
    u.c.name.label('User'), 
    ]) 
r = conn.execute(q).fetchall() 
log.debug(r[0].keys()) 
# [u'UserId', u'User'] 

# join the 2 aliased tables 
from_ = u.join(d) 
log.debug(from_.c.keys()) 
# [u'%(172847020 user)s_id', u'%(172847020 user)s_name', u'%(172847020 user)s_department_id', u'%(172846668 department)s_id', u'%(172846668 department)s_name'] 

# this does not work 
q = select([ 
    from_.c.user_id.label('UserId'), 
    from_.c.user_name.label('User'), 
    from_.c.department_name.label('Department'), 
    ]) 
r = conn.execute(q).fetchall() 
log.debug(r[0].keys()) 

Answer 1

q = select([ 
    u.c.id.label('UserId'), 
    u.c.name.label('User'), 
    d.c.name.label('Department'), 
], from_obj=u.join(d))