What's the proper way to return in an ORM query the value of a Postgres
array attribute at a given specific index within the array?
I have a db table with a column called value, which is a 2d array, defined
as REAL[][].
My ModelClass is defined as
class EmLine(Base):
__tablename__ = 'emline'
__table_args__ = {'autoload': True, 'schema': 'dapdb'}
def __repr__(self):
return '<EmLine (pk={0})'.format(self.pk)
value = Column(ARRAY(Float, dimensions=2, zero_indexes=True))
ivar = Column(ARRAY(Float, dimensions=2, zero_indexes=True))
mask = Column(ARRAY(Integer, dimensions=2, zero_indexes=True))
Pure SQL indexing an array works just fine
select e.value[16][17] from dapdb.emline as e;
But SQLalchemy does not
session.query(dapdb.EmLine.value[16][17]).first()
returns the error
NotImplementedError: Operator 'getitem' is not supported on this expression
I've tried defining a hybrid method/expression in my ModelClass, and running
session.query(dapdb.EmLine.singleat('value',16,17)).first()
but I'm getting the same "getitem" error
class EmLine(Base):
__tablename__ = 'emline'
__table_args__ = {'autoload': True, 'schema': 'mangadapdb'}
def __repr__(self):
return '<EmLine (pk={0})'.format(self.pk)
value = Column(ARRAY(Float, dimensions=2, zero_indexes=True))
ivar = Column(ARRAY(Float, dimensions=2, zero_indexes=True))
mask = Column(ARRAY(Integer, dimensions=2, zero_indexes=True))
@hybrid_method
def singleat(self, name, x, y):
param = self.__getattribute__(name)
return param[x][y]
@singleat.expression
def singleat(cls, name, x, y):
param = cls.__getattribute__(cls, name)
print(param, x, y)
return func.ARRAY(param)[x][y]
In my singleat expression, I've tried a variety of returns. return
func.ARRAY(param)[x][y] ; return param[x][y]. What's the proper syntax to
match the actual SQL array indexing?
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