SQLAlchemy加入複合外鍵（與flask-sqlalchemy）

Question

我想了解如何使用SQLAlchemy上的複合外鍵進行連接，並且我嘗試這樣做是失敗的。

我有我的玩具模型（我用的燒瓶SQLAlchemy的，但我不知道這有什麼關係問題）以下的模型類：然後我填充

# coding=utf-8 
from flask import Flask 
from flask.ext.sqlalchemy import SQLAlchemy 

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


class Asset(db.Model): 
    __tablename__ = 'asset' 
    user = db.Column('usuario', db.Integer, primary_key=True) 
    profile = db.Column('perfil', db.Integer, primary_key=True) 
    name = db.Column('nome', db.Unicode(255)) 

    def __str__(self): 
     return u"Asset({}, {}, {})".format(self.user, self.profile, self.name).encode('utf-8') 


class Zabumba(db.Model): 
    __tablename__ = 'zabumba' 

    db.ForeignKeyConstraint(
     ['asset.user', 'asset.profile'], 
     ['zabumba.user', 'zabumba.profile'] 
    ) 

    user = db.Column('usuario', db.Integer, primary_key=True) 
    profile = db.Column('perfil', db.Integer, primary_key=True) 
    count = db.Column('qtdade', db.Integer) 

    def __str__(self): 
     return u"Zabumba({}, {}, {})".format(self.user, self.profile, self.count).encode('utf-8') 

的數據庫與一些假的數據：

db.drop_all() 
db.create_all() 

db.session.add(Asset(user=1, profile=1, name=u"Pafúncio")) 
db.session.add(Asset(user=1, profile=2, name=u"Skavurska")) 
db.session.add(Asset(user=2, profile=1, name=u"Ermengarda")) 

db.session.add(Zabumba(user=1, profile=1, count=10)) 
db.session.add(Zabumba(user=1, profile=2, count=11)) 
db.session.add(Zabumba(user=2, profile=1, count=12)) 

db.session.commit() 

並試圖下面的查詢：

> for asset, zabumba in db.session.query(Zabumba).join(Asset).all(): 
>  print "{:25}\t<---->\t{:25}".format(asset, zabumba) 

乙UT SQLAlchemy的告訴我，它無法找到足夠的外鍵這個連接：

Traceback (most recent call last): 
    File "sqlalchemy_join.py", line 65, in <module> 
    for asset, zabumba in db.session.query(Zabumba).join(Asset).all(): 
    File "/home/calsaverini/.virtualenvs/recsys/local/lib/python2.7/site-packages/sqlalchemy/orm/query.py", line 1724, in join 
    from_joinpoint=from_joinpoint) 
    File "<string>", line 2, in _join 
    File "/home/calsaverini/.virtualenvs/recsys/local/lib/python2.7/site-packages/sqlalchemy/orm/base.py", line 191, in generate 
    fn(self, *args[1:], **kw) 
    File "/home/calsaverini/.virtualenvs/recsys/local/lib/python2.7/site-packages/sqlalchemy/orm/query.py", line 1858, in _join 
    outerjoin, create_aliases, prop) 
    File "/home/calsaverini/.virtualenvs/recsys/local/lib/python2.7/site-packages/sqlalchemy/orm/query.py", line 1928, in _join_left_to_right 
    self._join_to_left(l_info, left, right, onclause, outerjoin) 
    File "/home/calsaverini/.virtualenvs/recsys/local/lib/python2.7/site-packages/sqlalchemy/orm/query.py", line 2056, in _join_to_left 
    "Tried joining to %s, but got: %s" % (right, ae)) 
sqlalchemy.exc.InvalidRequestError: Could not find a FROM clause to join from. Tried joining to <class '__main__.Asset'>, but got: Can't find any foreign key relationships between 'zabumba' and 'asset'. 

我試着像一些其他的東西：宣佈兩個表上ForeignKeyConstraint或反向查詢，以db.session.query(Asset).join(Zabumba).all()。

我在做什麼錯？

謝謝。

---

PS：在我真正的應用程序代碼的問題實際上是一個有點複雜，因爲這些表在不同的模式，我將使用綁定的東西：

app.config['SQLALCHEMY_BINDS'] = { 
    'assets':  'mysql+mysqldb://fooserver/assets', 
    'zabumbas':  'mysql+mysqldb://fooserver/zabumbas', 
} 

然後我將在表上聲明不同的綁定。那麼我應該如何聲明ForeignKeyConstraint？

Answer 1

您的代碼有幾個錯別字，糾正這將使整個代碼工作。

正確的ForeignKeyConstraint定義：

• 它不只是定義它，你必須將它添加到__table_args__定義
• 列和refcolumns參數逆轉（見documentation ）
• 列的名稱必須是數據庫中的名稱，而不是ORM屬性的名稱

如圖以下代碼：由查詢子句中具有兩個類

class Zabumba(db.Model): 
    __tablename__ = 'zabumba' 

    __table_args__ = (
     db.ForeignKeyConstraint(
      ['usuario', 'perfil'], 
      ['asset.usuario', 'asset.perfil'], 
     ), 
    ) 

構建適當的查詢：

for asset, zabumba in db.session.query(Asset, Zabumba).join(Zabumba).all(): 
     print "{:25}\t<---->\t{:25}".format(asset, zabumba)