I have the following two models
class Dataset(db.Model):
__tablename__ = 'datasets'
id = db.Column(db.Integer, primary_key=True)
creation_datetime = db.Column(db.DateTime(timezone=False), nullable=
False)
sample_id = db.Column(db.Integer, db.ForeignKey('samples.id'), nullable=
False, index=True)
sample = db.relationship('Sample', uselist=False, innerjoin=True)
class Sample(db.Model):
__tablename__ = 'samples'
id = db.Column(db.Integer, primary_key=True)
datasets = db.relationship('Dataset')
num_datasets = column_property(
select([func.count(Dataset.id)]).where(Dataset.sample_id == id).
correlate_except(Dataset)
)
A sample has many datasets. I would like to add a property "is_latest" to
Dataset, probably as a column_property, which is true if the dataset has
the latest creation_datetime of the datasets associated with its sample. In
other words, if a sample has three datasets, the dataset whose
creation_datetime is largest should have is_latest=True and the other two
should have is_latest=False
If ordering by creation_datetime isn't possible/easy, ordering by primary
key is also acceptable. How can I construct this column_property?
One of the issues I've encountered while trying to make this work is that
there's a circular dependency between the two models. Since the Sample
model uses Dataset in its num_datasets property, the Dataset class is
currently defined first. But this means that it can't refer to Sample in
its own properties
Thanks for the help
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