没有外键的SQLAlchemy经典关系

Question

I'm trying to relate two tables that have multiple 'secondary' tables. Instead of the declarative syntax, it's necessary that I use the classical. Here is a simplified schema:

class Apple:
  def __init__(self, id=None, name=None):
    # ...

class Recipe:
  def __init__(self, id=None, appleId=None, name=None):
    # ...

class Blog:
  def __init__(self, id=None, name=None, recipeId=None, bloggerId=None):
    # ...

class Blogger:
  def __init__(self, name)
    # ...

appleTable = Table('Apple', metadata, Column('id', Integer, primary_key=True), Column('name', String(256)))
recipeTable = Table('Recipe', metadata, Column('id', Integer, primary_key=True), Column('name', String(256)), Column('appleId', Integer, ForeignKey('Apple.id')))
blogTable = Table('Blog', metadata, Column('id', Integer, primary_key=True), Column('name', String(256)), Column('recipeId', Integer, ForeignKey('Recipe.id')), Column('bloggerId', Integer, ForeignKey('Blogger.id')) ) 
bloggerTable = Table('Blogger', metadata, Column('id', Integer, primary_key=True), Column('name', String(256)))


# call mapper on all tables/classes
# ... #

# Relate 'Apple' to 'Blogger' using 'Recipe' and 'Blog' as intermediates 
Apple.appleBloggers = relationship(Blogger, secondary=..., primaryjoin=..., secondaryjoin=...)

What relationship would I need to place into the appleBloggers attribute of Apple in order to retrieve all bloggers who've blogged about apple recipes?

---

Edit: Solution

An alternative @univerio 's solution is posted below. The difference being with the usage of the mapped objects vs the table variables. I've also added a viewonly parameter, which prevents writes to the attribute.

mapper(Apple, appleTable, properties = {
  "appleBloggers": relationship(Blogger,
            secondary=join(Recipe, Blog, Recipe.id == Blog.recipeId),
            secondaryjoin=lambda: and_(Apple.id == Recipe.appleId, Blogger.id == Blog.bloggerId),
            viewonly=True)
})

---

Original Attempt

Here is what I've tried:

Apple.appleBloggers = relationship(Blogger, 
    secondary=join(Recipe, Blog, Recipe.id==Blog.recipeId),
    primaryjoin= Apple.id == Recipe.appleId,
    secondaryjoin= Blog.bloggerId == Blogger.id)

But whenever I do the following:

apple = Apple(name="RedDelicious")
session.add(apple)
session.commit()
print(apple.appleBloggers)

I get the error:

File ".../.pyenv/versions/2.7.10/lib/python2.7/site-packages/sqlalchemy/orm/relationships.py", line 1425, in __str__
  return str(self.parent.class_.__name__) + "." + self.key
File ".../.pyenv/versions/2.7.10/lib/python2.7/site-packages/sqlalchemy/util/langhelpers.py", line 840, in __getattr__
  return self._fallback_getattr(key)
File ".../.pyenv/versions/2.7.10/lib/python2.7/site-packages/sqlalchemy/util/langhelpers.py", line 818, in _fallback_getattr
  raise AttributeError(key)
AttributeError: parent

Answer 1

You're mixing declarative and classical mappings. Assigning a relationship like that only works for declarative. The proper way to do this in classical mapping is:

mapper(Apple, appleTable, properties={
    "appleBloggers": relationship(Blogger,
                                  secondary=recipeTable.join(blogTable, recipeTable.c.id == blogTable.c.recipeId),
                                  primaryjoin=appleTable.c.id == recipeTable.c.appleId,
                                  secondaryjoin=blogTable.c.bloggerId == bloggerTable.c.id)
})

Alternative Solution (with mapped objects):

mapper(Apple, appleTable, properties = {
  "appleBloggers": relationship(Blogger,
            secondary=join(Recipe, Blog, Recipe.id == Blog.recipeId),
            secondaryjoin=lambda: and_(Apple.id == Recipe.appleId, Blogger.id == Blog.bloggerId),
            viewonly=True)
})