filtering by association attributes with SqlAlchemy association_proxy

问题

I have a many-to-many (developers & projects) relationship modeled using SA's association_proxy. The collections (developers on each project & projects for each developer) work fine, but I need to filter on an attribute of the association itself (status). Something like this (which does not work):

activeDevelopers = s.query(Developer).filter_by(Developer.developerProjects.status == 'active').all()

What am I missing? Here is the complete test code:

import logging
from sqlalchemy import create_engine, Table, Column, Integer, String, MetaData, ForeignKey
from sqlalchemy.orm import relation, mapper, sessionmaker
from sqlalchemy.sql import *
from sqlalchemy.ext.associationproxy import association_proxy

log = logging.getLogger('nm_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

developer_table = Table('developer', meta,
    Column('id', Integer, primary_key=True, autoincrement = False),
    Column('name', String),
)

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

developer_project_table = Table('developer_project', meta,
    Column('developer_id', Integer, ForeignKey('developer.id'), primary_key = True),
    Column('project_id', Integer, ForeignKey('project.id'), primary_key = True),
    Column('status', String)
)

class Developer(object):
    projects = association_proxy('developerProjects', 'projects')
    def __str__(self):
        return 'Developer id:%i, name:%s' % (self.id, self.name)

class Project(object):
    developers = association_proxy('developerProjects', 'developers')
    def __str__(self):
        return 'Project id:%i, name:%s' % (self.id, self.name)

class DeveloperProject(object):
    def __str__(self):
        return 'DeveloperProject developer:%s, project:%s, status:%s' % (self.developer_id, self.project_id, self.status)

mapper(Developer, developer_table, properties = {
    'developerProjects':relation(DeveloperProject, backref = "developers")
})

mapper(Project, project_table, properties = {
    'developerProjects':relation(DeveloperProject, backref = "projects")
})

mapper(DeveloperProject, developer_project_table)

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

conn.execute(project_table.insert(),[
    {'name':'stackoverflow'},
    {'name':'superuser'},
])
conn.execute(developer_table.insert(),[
    {'name':'John'},
    {'name': 'TerryJ'},
    {'name': 'TerryG'},
    {'name': 'Eric'},
    {'name': 'Graham'},
])
conn.execute(developer_project_table.insert(),[
    {'developer_id':1, 'project_id':1, 'status':'active'},
    {'developer_id':2, 'project_id':2, 'status':'inactive'},
    {'developer_id':3, 'project_id':2, 'status':'active'},
    {'developer_id':4, 'project_id':1, 'status':'active'},
    {'developer_id':4, 'project_id':2, 'status':'active'},
    {'developer_id':5, 'project_id':1, 'status':'active'},
    {'developer_id':5, 'project_id':2, 'status':'inactive'},
])

Session = sessionmaker(bind=engine)
s = Session()

developers = s.query(Developer).all()
projects = s.query(Project).all()

for d in developers:
    log.debug(d)
    for p in d.projects:
        log.debug('    %s' % p)

for p in projects:
    log.debug(p)
    for d in p.developers:
        log.debug('    %s' % d)

# does not work
activeDevelopers = s.query(Developer).filter_by(Developer.developerProjects.status == 'active').all()
# AttributeError: Neither 'InstrumentedAttribute' object nor 'Comparator' object has an attribute 'status'

回答1:

Use any() method of association proxy:

s.query(Developer).filter(Developer.developerProjects.any(status='active'))

回答2:

To add to Denis's answer:

When I tried the any() method, I got this error

sqlalchemy.exc.InvalidRequestError: 'any()' not implemented for scalar attributes. Use has().

Using has() instead of any() worked for me.

It looks like any() is for list relationships (in this case Developers potentially have multiple projects so Developer.developerProjects is a list). Whereas has() is for a single relationship (for instance if a Developer had one Workplace associated).

Here is the link to documentation: http://docs.sqlalchemy.org/en/latest/orm/internals.html#sqlalchemy.orm.properties.RelationshipProperty.Comparator.has

来源：https://stackoverflow.com/questions/4572679/filtering-by-association-attributes-with-sqlalchemy-association-proxy

标签

sql

many-to-many

sqlalchemy