I would like to create an association between a Dataset object and all
Category objects through an intermediate Annotation table.
A Dataset contains a collection of Annotations. Each Annotation has a
single Category. I want Dataset.categories to contain the unique set of
Categories made up of all the Categories of all the Annotations in that
Dataset. I have tried doing this with a double association table (
dataset_categories), but it is not working. What is the right way to do
this? Here is my code so far:
Base = declarative_base()
dataset_categories = Table('dataset_categories', Base.metadata,
Column('dataset_id', Integer, ForeignKey('datasets.id')),
Column('annotation_id', Integer, ForeignKey('annotations.id')),
Column('category_id', Integer, ForeignKey('categories.id')))
class Dataset(Base):
__tablename__ = 'datasets'
id = Column(Integer, primary_key=True)
annotations = relationship("Annotation")
categories = relationship("Category", secondary=dataset_categories)
class Annotation(Base):
__tablename__ = 'annotations'
id = Column(Integer, primary_key=True)
category_id = Column(Integer, ForeignKey('categories.id'), nullable=False)
category = relationship("Category")
dataset_id = Column(Integer, ForeignKey('datasets.id'))
class Category(Base):
__tablename__ = 'categories'
id = Column(Integer, primary_key=True)
name = Column(String, nullable=False, unique=True)
dataset = relationship("Dataset", secondary=dataset_categories)
dataset_id = Column(Integer, ForeignKey('datasets.id'),
back_populates='categories')
--
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http://www.sqlalchemy.org/
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