That's the normal mechanics of how the ORM does inserts. For columns that
have no default value, it supplies None explicitly. There's some obscure
history behind that and I'm not sure there's much of a rationale beyond
that it makes it easier to cache the INSERT statement and make use of
executemany(). Its been that way for over 10 years so I'm not quick to
just change those things unless it is really causing a problem.
If these columns have a server side behavior for INSERT then you'd also add
server_default=FetchedValue() and then you wouldn't see the None on INSERT.
On Feb 4, 2018 5:43 AM, "Lele Gaifax" <l...@metapensiero.it> wrote:
Hi all,
I have a PG database with tables like the following
Column | Type | Modifiers
---------+-----------------------------+--------------------
----------------------
id | uuid | not null default uuid_generate_v1()
created | timestamp without time zone | not null default
transaction_timestamp()
changed | timestamp without time zone |
name | character varying(192) | not null
code | character varying(64) | not null
value | integer |
with a trigger that updates the "changed" field whenever a record is
modified.
Accordingly to the documentation[1] I thus modelled it like in the following
way:
import sqlalchemy as sa
import sqlalchemy.orm as orm
import sqlalchemy.types as types
import sqlalchemy.dialects.postgresql as sapg
md = sa.MetaData()
testtable = sa.Table(
'testtable', md,
sa.Column('id', sapg.UUID(True),
primary_key=True,
nullable=False,
server_default=sa.func.uuid_generate_v1()),
sa.Column('created', types.DateTime(),
nullable=False,
server_default=sa.func.transaction_timestamp()),
sa.Column('changed', types.DateTime(),
server_onupdate=sa.FetchedValue()),
sa.Column('name', types.Unicode(192),
nullable=False),
sa.Column('code', types.Unicode(64),
nullable=False),
sa.Column('value', types.Integer,
nullable=True))
class Base:
def __init__(self, **kwargs):
cls_ = type(self)
for k in kwargs:
setattr(self, k, kwargs[k])
class TestTable(Base):
pass
orm.mapper(TestTable, testtable)
This works, but I notice that SA explicitly inserts the "changed" field
with a
None value on INSERTs, that is the following snippet:
e = sa.create_engine('postgresql://localhost/test', echo=True)
md.create_all(e)
s = orm.Session(e)
o1 = TestTable(name='foo', code='bar')
s.add(o1)
s.commit()
produces a log like the following:
2018-02-04 11:34:12,464 INFO sqlalchemy.engine.base.Engine INSERT INTO
testtable (changed, name, code, value) VALUES (%(changed)s, %(name)s,
%(code)s, %(value)s) RETURNING testtable.id
2018-02-04 11:34:12,464 INFO sqlalchemy.engine.base.Engine {'changed':
None, 'name': 'foo', 'code': 'bar', 'value': None}
The doubt is: why is SA providing explicit None values for both "changed"
and
"value" fields? Am I missing something in the table description or what?
Thanks in advance for any enlightenment!
ciao, lele.
[1] http://docs.sqlalchemy.org/en/latest/core/defaults.html#
triggered-columns
--
nickname: Lele Gaifax | Quando vivrò di quello che ho pensato ieri
real: Emanuele Gaifas | comincerò ad aver paura di chi mi copia.
l...@metapensiero.it | -- Fortunato Depero, 1929.
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http://www.sqlalchemy.org/
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