hi,

I would like to represent an existing database and its associations in
sqlalchemy. Unfortunately, it has many flows, like two tables are related
via a substring from one table.

something like this

class ParentClass:
  id = ...
  type = ...

class ChildClass:
  nr_proforma = Column('', String)
  type = ...

  parent_id = column_property(
        select([ParentClass.id])\
            .where(ParentClass.id==cast(func.substring(nr_proforma + ' from
3'), Integer))\
            .where(ParentClass.type==type),
        deferred=False
        )

I hope the above example describes well what I would like to achieve,
unfortunately, the resulting sql is not what I would like, as nr_proforma is
'misinterpreted'

The resulting query is:
SELECT documenteiesire."IDDoc" \nFROM documenteiesire \nWHERE
documenteiesire."IDDoc" = CAST(substring(documentedelucru."NrProforma" ||
%(NrProforma_1)s) AS INTEGER) AND documenteiesire."Tip" =
documentedelucru."Tip"

another alternative

  parent_id = column_property(
        select([ParentClass.id])\
            .where(ParentClass.id==cast(func.substring('%s from 3' %
nr_proforma), Integer))\
            .where(ParentClass.type==type),
        deferred=False
        )
results in
SELECT documenteiesire."IDDoc" \nFROM documenteiesire \nWHERE
documenteiesire."IDDoc" = CAST(substring(%(substring_1)s) AS INTEGER
with
'substring_1': 'NrProforma from 3'

any ideas?
Viktor

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