KeyError when adding objects using an association proxy

[Stephan Hügel]

I have two objects, which I'm joining using an association proxy:

(doing this using Flask-sqlalchemy, so Base, engine etc are implicit)

class Correspondent(db.Model, GlyphMixin):
    # PK column and tablename etc. come from the mixin
    name = db.Column(db.String(100), nullable=False, unique=True)
    # association proxy
    tablets = association_proxy('correspondent_tablets', 'tablet')

def __init__(self, name, tablets=None):
    self.name = name
    if tablets:
        self.tablets = tablets


class Tablet(db.Model, GlyphMixin):
    # PK column and tablename etc. come from the mixin
    area = db.Column(db.String(100), nullable=False, unique=True)
    # association proxy
    correspondents = association_proxy('tablet_correspondents', 'correspondent')

def __init__(self, area, correspondents=None):
    self.area = area
    if correspondents:
        self.correspondents = correspondents


class Tablet_Correspondent(db.Model):

    __tablename__ = "tablet_correspondent"
    tablet_id = db.Column("tablet_id",
        db.Integer(), db.ForeignKey("tablet.id"), primary_key=True)
    correspondent_id = db.Column("correspondent_id",
        db.Integer(), db.ForeignKey("correspondent.id"), primary_key=True)
    # relations
    tablet = db.relationship(
        "Tablet",
        backref="tablet_correspondents",
        cascade="all, delete-orphan",
        single_parent=True)
    correspondent = db.relationship(
        "Correspondent",
        backref="correspondent_tablets",
        cascade="all, delete-orphan",
        single_parent=True)

    def __init__(self, tablet=None, correspondent=None):
        self.tablet = tablet

        self.correspondent = correspondent

However, I get a KeyError when I try to append an object (new or existing) to the Tablet.correspondents or Correspondent.tablets collection. I assume I've done something wrong when implementing the relationships and backrefs on the Tablet_Correspondent model – I was following the association proxy examples, but wanted it to be more symmetrical than the User.keywords example, which is where I'm going wrong, I suspect.

 

[Michael Bayer]

At the very least I would need a full stack trace, exactly how you are appending objects, and preferably the means to actually run it.   Nothing is obviously wrong.    Can you distill your failure into a no-dependencies .py file?  For example I don't have GlyphMixin here, the formatting for __init__ seems to be off in this paste, etc, I don't see how you're manipulating the collection, etc.   No engine is needed since this is just an association proxy creation issue.

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[Stephan Hügel]

On Tuesday, 19 June 2012 00:14:57 UTC+1, Michael Bayer wrote:

At the very least I would need a full stack trace, exactly how you are appending objects, and preferably the means to actually run it.   Nothing is obviously wrong.    Can you distill your failure into a no-dependencies .py file?  For example I don't have GlyphMixin here, the formatting for __init__ seems to be off in this paste, etc, I don't see how you're manipulating the collection, etc.   No engine is needed since this is just an association proxy creation issue.

Mike,

no-dep python file and stack trace are at https://gist.github.com/174a76acf27ffef1b66d 

In order to reproduce the issue, I query for two objects:

tab = Tablet.query.first()

cor = Correspondent.query.first()

If I do tab.correspondents or cor.tablets I just get back an empty list in both cases (as expected)

If I do tab.correspondents.append(cor), I get the KeyError you see in line 3 of the stack trace.

-- 

steph

[Stephan Hügel]

Mike,

no-dep python file and stack trace are at https://gist.github.com/174a76acf27ffef1b66d 

In order to reproduce the issue, I query for two objects:

tab = Tablet.query.first()

cor = Correspondent.query.first()

If I do tab.correspondents or cor.tablets I just get back an empty list in both cases (as expected)

If I do tab.correspondents.append(cor), I get the KeyError you see in line 3 of the stack trace.

-- 

steph

As has been pointed out here, I wasn't using the creator lambda while attempting to create the objects in the association object. Problem would have been solved by RTFM, as per usual, and everything's working as expected now.

[Michael Bayer]

great, glad my lack of time to get to this ultimately got it solved ;)

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