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python - 基于排除关系中的项目的 Sqlalchemy 查询

问题描述

我有一个PartyOrganiser（s）表，一个Contact（s）表和一个有组织Party（s）表。

PartyOrganisertoParty是一对多的。
PartyOrganisertoContact是一对多的。
PartytoContact是多对多的，带有关联表。

class PartyOrganiser(db.Model):
    __tablename__ = 'party_organiser'
    id   = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String)
    parties  = db.relationship("Party",    back_populates='party_organiser')
    contacts = db.relationship("Contacts", back_populates='party_organiser')

contact_party_ass_tab = db.Table('contact_party', db.Model.metadata,
    db.Column('party_id', db.Integer, db.ForeignKey('party.id')),
    db.Column('contact_id', db.Integer, db.ForeignKey('contact.id')))

class Party(db.Model):
    __tablename__ = 'party'
    id      = db.Column(db.Integer, primary_key=True)
    details = db.Column(db.String)
    party_organiser_id = db.Column(db.Integer, db.ForeignKey('party_organiser.id'), nullable=False)
    party_organiser = db.relationship("PartyOrganiser", back_populates="parties", uselist=False)
    attendees = db.relationship("Contact", secondary=contact_party_ass_tab, back_populates='intended_parties')

class Contact(db.Model):
    __tablename__ = 'contact'
    id   = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String)
    party_organiser_id = db.Column(db.Integer, db.ForeignKey('party_organiser.id'), nullable=False)
    party_organiser = db.relationship("PartyOrganiser", back_populates="parties", uselist=False)
    intended_parties = db.relationship("Contact", secondary=contact_party_ass_tab, back_populates='attendees')

主要问题：

从语法上讲，对于特定的聚会，我想获取与聚会组织者相关但尚未参加聚会的那些联系人的列表。即称他们为potential_attendees，我希望以下作为SQLalchemy 查询风格的解决方案：

class Party(db.model):
    ...
    @property
    def potential_attendees(self):
        # get all contacts for the right party_organiser
        sub_query = Contact.query.filter(Contact.party_organiser_id == self.party_organiser_id)
        # then eliminate those that are already attendees to this party..
        return sub_query.difference(self.attendees) # <- pseudocode

子问题：

此配置在和PartyOrganiser之间具有固有的 3 向约束： 聚会和参加者只有在共享party_organiser 时才能关联。即 PartyOrganiser1 的联系人都不能成为 PartyOrganiser2 组织的 Party2 的参与者。对我来说，上述格式的要求并不明显。事实上，我相信它不是。我将如何实现这个约束？PartyContact

标签： pythonsqlalchemymany-to-manyrelational-database

解决方案

NOT EXISTS您可以使用连接表上的构造来查询关系中排除的项目。

@property
def potential_attendees(self):
    sq = db.session.query(contact_party_ass_tab.columns.contact_id).subquery()
    return db.session.query(Contact).filter(
            Contact.party_organiser_id==self.party_organiser_id,
            ~exists().where(sq.c.contact_id==Contact.id)
        ).all()

就您的其他问题而言，您可以通过为 Party.attendees 和 Contact.intended_pa​​rties 添加属性级别验证器并确保添加到这些列表中的任何新项目具有匹配的 party_organiser_id 来对该 ORM 级别施加该约束。这是完整的代码

from flask import Flask
from flask.ext.sqlalchemy import SQLAlchemy
from sqlalchemy import exists

from sqlalchemy.orm import validates


app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///:memory:'
db = SQLAlchemy(app)

class PartyOrganiser(db.Model):
    __tablename__ = 'party_organiser'
    id   = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String)
    parties  = db.relationship("Party",    back_populates='party_organiser')
    contacts = db.relationship("Contact", back_populates='party_organiser')

    def __repr__(self):
        return self.name


contact_party_ass_tab = db.Table('contact_party', db.Model.metadata,
    db.Column('party_id', db.Integer, db.ForeignKey('party.id')),
    db.Column('contact_id', db.Integer, db.ForeignKey('contact.id')))

class Party(db.Model):
    __tablename__ = 'party'
    id      = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String)
    details = db.Column(db.String)
    party_organiser_id = db.Column(db.Integer, db.ForeignKey('party_organiser.id'), nullable=False)
    party_organiser = db.relationship("PartyOrganiser", back_populates="parties", uselist=False)
    attendees = db.relationship("Contact", secondary=contact_party_ass_tab, back_populates='intended_parties')

    def __repr__(self):
        return self.name

    @property
    def potential_attendees(self):
        sq = db.session.query(contact_party_ass_tab.columns.contact_id).subquery()
        return db.session.query(Contact).filter(
                Contact.party_organiser_id==self.party_organiser_id,
                ~exists().where(sq.c.contact_id==Contact.id)
            ).all()

    @validates('attendees')
    def validate_attendee(self, key, attendee):
        assert attendee.party_organiser_id == self.party_organiser_id
        return attendee

class Contact(db.Model):
    __tablename__ = 'contact'
    id   = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String)
    party_organiser_id = db.Column(db.Integer, db.ForeignKey('party_organiser.id'), nullable=False)
    party_organiser = db.relationship("PartyOrganiser", back_populates="contacts", uselist=False)
    intended_parties = db.relationship("Party", secondary=contact_party_ass_tab, back_populates='attendees')

    def __repr__(self):
        return self.name

    @validates('intended_parties')
    def validate_party(self, key, party):
        assert party.party_organiser_id == self.party_organiser_id
        return party

db.create_all()

organiser1 = PartyOrganiser(name="organiser1")
organiser2 = PartyOrganiser(name="organiser2")

db.session.add_all([organiser1, organiser2])
db.session.commit()


org1_party1 = Party(name="Organiser1's Party1", party_organiser_id=organiser1.id)
org1_party2 = Party(name="Organiser1's Party2", party_organiser_id=organiser1.id)

org2_party1 = Party(name="Organiser2's Party1", party_organiser_id=organiser2.id)
org2_party2 = Party(name="Organiser2's Party2", party_organiser_id=organiser2.id)

db.session.add_all([org1_party1, org1_party2, org2_party1, org2_party2])
db.session.commit()

org1_contact1 = Contact(name="Organiser1's contact 1", party_organiser_id=organiser1.id)
org1_contact2 = Contact(name="Organiser1's contact 2", party_organiser_id=organiser1.id)
org1_contact3 = Contact(name="Organiser1's contact 3", party_organiser_id=organiser1.id)
org1_contact4 = Contact(name="Organiser1's contact 4", party_organiser_id=organiser1.id)

org2_contact1 = Contact(name="Organiser2's contact 1", party_organiser_id=organiser2.id)
org2_contact2 = Contact(name="Organiser2's contact 2", party_organiser_id=organiser2.id)
org2_contact3 = Contact(name="Organiser2's contact 3", party_organiser_id=organiser2.id)
org2_contact4 = Contact(name="Organiser2's contact 4", party_organiser_id=organiser2.id)

db.session.add_all([org1_contact1, org1_contact2, org1_contact3, org1_contact4, org2_contact1, org2_contact2, org2_contact3, org2_contact4])
db.session.commit()

org1_party1.attendees.append(org1_contact1)
db.session.commit()

print "Potential attendees of org1_party1 ", org1_party1.potential_attendees

print "Attempting to add a contact of a different organiser. Will throw exception"

org1_party1.attendees.append(org2_contact1)

输出（检查上面代码最后一行抛出的异常）：

In [1]: from exclusion_query import *
/home/surya/Envs/inkmonk/local/lib/python2.7/site-packages/flask_sqlalchemy/__init__.py:794: FSADeprecationWarning: SQLALCHEMY_TRACK_MODIFICATIONS adds significant overhead and will be disabled by default in the future.  Set it to True or False to suppress this warning.
  'SQLALCHEMY_TRACK_MODIFICATIONS adds significant overhead and '
Potential attendees of org1_party1  [Organiser1's contact 2, Organiser1's contact 3, Organiser1's contact 4]
Attempting to add a contact of a different organiser. Will throw exception
---------------------------------------------------------------------------
AssertionError                            Traceback (most recent call last)
<ipython-input-1-4380704ace46> in <module>()
----> 1 from exclusion_query import *

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