Re: [sqlalchemy] recursive cte use current row as anchor
changing it more the way you had
lineage_nodes = recursive_cte.union_all(
select([s.c.id, s.c._enabling_factor, s.c.selfreferencing_staff_id])
.join(
recursive_cte, recursive_cte.c.selfreferencing_staff_id == s.c.id
)
.filter(recursive_cte.c._enabling_factor == None)
)
produces:
WITH RECURSIVE lineage_nodes(anchor_id, _enabling_factor,
selfreferencing_staff_id) AS
(SELECT anchor_s.id AS anchor_id, anchor_s._enabling_factor AS
_enabling_factor, anchor_s.selfreferencing_staff_id AS selfreferencing_staff_id
FROM staff AS anchor_s UNION ALL SELECT s.id AS id, s._enabling_factor AS
_enabling_factor, s.selfreferencing_staff_id AS selfreferencing_staff_id
FROM staff AS s JOIN lineage_nodes ON lineage_nodes.selfreferencing_staff_id =
s.id
WHERE lineage_nodes._enabling_factor IS NULL)
SELECT staff.id AS staff_id, staff.selfreferencing_staff_id AS
staff_selfreferencing_staff_id, staff._enabling_factor AS
staff__enabling_factor, staff.record_id AS staff_record_id, (SELECT
final_s._enabling_factor
FROM staff AS final_s
WHERE final_s.record_id = (SELECT min(lineage_nodes.anchor_id) AS min_1
FROM lineage_nodes
WHERE lineage_nodes.anchor_id = staff.id)) AS anon_1
FROM staff
so the UNION joins out to "lineage_nodes" again. I've not really worked with
recursive CTEs much but i think that's the idea.
On Sun, Sep 26, 2021, at 4:01 PM, Mike Bayer wrote:
> i applied an alias to the CTE before unioning it, please take that out and
> try again. CTE inside the subquery can't happen, but shoudnt be necessary.
>
> On Sun, Sep 26, 2021, at 3:53 PM, niuji...@gmail.com wrote:
>> Hi Mike,
>> This code doesn't seem to yield desired result, now all the
>> `effective_enabling_factor` is `None`, except for those rows that carries a
>> `_enabling_factor` on itself. In other words, it doesn't seem to recusively
>> search the next immediately parent's marker at all.
>>
>> And the SQL it generates is a little confusing, it seems to me that we
>> introduce a `recursive_cte_a` aliased table and gain nothing from it:
>>
>> WITH RECURSIVE lineage_nodes(
>> anchor_id, _enabling_factor, selfreferencing_staff_id
>> ) AS (
>> SELECT
>> anchor_f.id AS anchor_id,
>> anchor_f._enabling_factor AS _enabling_factor,
>> anchor_f.selfreferencing_staff_id AS selfreferencing_staff_id
>> FROM
>> staff AS anchor_f
>> UNION ALL
>> SELECT
>> anchor_f.id AS id,
>> anchor_f._enabling_factor AS _enabling_factor,
>> anchor_f.selfreferencing_staff_id AS selfreferencing_staff_id
>> FROM
>> staff AS anchor_f
>> JOIN lineage_nodes AS anon_2 ON anon_2.selfreferencing_staff_id =
>> anchor_f.id
>> WHERE
>> anon_2._enabling_factor IS NULL
>> )
>> SELECT
>> staff.id AS staff_id,
>> staff._enabling_factor AS staff__enabling_factor,
>> (
>> SELECT
>> final_f._enabling_factor
>> FROM
>> staff AS final_f
>> WHERE
>> final_f.id = (
>> SELECT
>> min(lineage_nodes.anchor_id) AS min_1
>> FROM
>> lineage_nodes
>> WHERE
>> lineage_nodes.anchor_id = staff.id
>> )
>> ) AS anon_1
>> FROM
>> staff
>>
>>
>> On Sunday, September 26, 2021 at 7:35:20 AM UTC-7 Mike Bayer wrote:
>>> __
>>> OK there's various small issues here but overall SQLAlchemy's new "nesting"
>>> feature does not seem to work correctly yet for a RECURSIVE CTE with UNION,
>>> meaning it's not very useful for RECURSIVE right now.
>>>
>>> But here's the thing, I'm not as SQL expert as some people think but I
>>> don't think it should be necessary for a CTE to actually be embedded in a
>>> subquery. You can keep the CTE on top, where it can more efficiently
>>> create a set of all rows, and then refer to it within a normal correlated
>>> subquery that's in the column_property().
>>>
>>> ive written the below MCVE we can work with going forward. see how close
>>> this is, but the goal is, keep the CTE on top as it normally can be and do
>>> correlations outside of it.
>>>
>>> from sqlalchemy import Column
>>> from sqlalchemy import ForeignKey
>>> from sqlalchemy import func
>>> from sqlalchemy import Integer
>>> from sqlalchemy import select
>>> from sqlalchemy.ext.declarative import declarative_base
>>> from sqlalchemy.orm import backref
>>> from sqlalchemy.orm import column_property
>>> from sqlalchemy.orm import relationship
>>> from sqlalchemy.orm import Session
>>>
>>> Base = declarative_base()
>>>
>>>
>>> class Staff(Base):
>>> __tablename__ = "staff"
>>>
>>> id = Column(Integer, primary_key=True)
>>>
>>> selfreferencing_staff_id = Column(
>>> Integer,
>>> ForeignKey("staff.id", onupdate="CASCADE", ondelete="SET NULL"),
>>> )
>>> _enabling_factor = Column(Integer)
>>> record_id = Column(Integer)
>>>
>>> team_members = relationship(
>>> "Staff", backref=backref("supervisor", remote_side="Staff.id")
>>> )
>>>
>>>
>>>
Re: [sqlalchemy] recursive cte use current row as anchor
i applied an alias to the CTE before unioning it, please take that out and try
again. CTE inside the subquery can't happen, but shoudnt be necessary.
On Sun, Sep 26, 2021, at 3:53 PM, niuji...@gmail.com wrote:
> Hi Mike,
> This code doesn't seem to yield desired result, now all the
> `effective_enabling_factor` is `None`, except for those rows that carries a
> `_enabling_factor` on itself. In other words, it doesn't seem to recusively
> search the next immediately parent's marker at all.
>
> And the SQL it generates is a little confusing, it seems to me that we
> introduce a `recursive_cte_a` aliased table and gain nothing from it:
>
> WITH RECURSIVE lineage_nodes(
> anchor_id, _enabling_factor, selfreferencing_staff_id
> ) AS (
> SELECT
> anchor_f.id AS anchor_id,
> anchor_f._enabling_factor AS _enabling_factor,
> anchor_f.selfreferencing_staff_id AS selfreferencing_staff_id
> FROM
> staff AS anchor_f
> UNION ALL
> SELECT
> anchor_f.id AS id,
> anchor_f._enabling_factor AS _enabling_factor,
> anchor_f.selfreferencing_staff_id AS selfreferencing_staff_id
> FROM
> staff AS anchor_f
> JOIN lineage_nodes AS anon_2 ON anon_2.selfreferencing_staff_id =
> anchor_f.id
> WHERE
> anon_2._enabling_factor IS NULL
> )
> SELECT
> staff.id AS staff_id,
> staff._enabling_factor AS staff__enabling_factor,
> (
> SELECT
> final_f._enabling_factor
> FROM
> staff AS final_f
> WHERE
> final_f.id = (
> SELECT
> min(lineage_nodes.anchor_id) AS min_1
> FROM
> lineage_nodes
> WHERE
> lineage_nodes.anchor_id = staff.id
> )
> ) AS anon_1
> FROM
> staff
>
>
> On Sunday, September 26, 2021 at 7:35:20 AM UTC-7 Mike Bayer wrote:
>> __
>> OK there's various small issues here but overall SQLAlchemy's new "nesting"
>> feature does not seem to work correctly yet for a RECURSIVE CTE with UNION,
>> meaning it's not very useful for RECURSIVE right now.
>>
>> But here's the thing, I'm not as SQL expert as some people think but I don't
>> think it should be necessary for a CTE to actually be embedded in a
>> subquery. You can keep the CTE on top, where it can more efficiently create
>> a set of all rows, and then refer to it within a normal correlated subquery
>> that's in the column_property().
>>
>> ive written the below MCVE we can work with going forward. see how close
>> this is, but the goal is, keep the CTE on top as it normally can be and do
>> correlations outside of it.
>>
>> from sqlalchemy import Column
>> from sqlalchemy import ForeignKey
>> from sqlalchemy import func
>> from sqlalchemy import Integer
>> from sqlalchemy import select
>> from sqlalchemy.ext.declarative import declarative_base
>> from sqlalchemy.orm import backref
>> from sqlalchemy.orm import column_property
>> from sqlalchemy.orm import relationship
>> from sqlalchemy.orm import Session
>>
>> Base = declarative_base()
>>
>>
>> class Staff(Base):
>> __tablename__ = "staff"
>>
>> id = Column(Integer, primary_key=True)
>>
>> selfreferencing_staff_id = Column(
>> Integer,
>> ForeignKey("staff.id", onupdate="CASCADE", ondelete="SET NULL"),
>> )
>> _enabling_factor = Column(Integer)
>> record_id = Column(Integer)
>>
>> team_members = relationship(
>> "Staff", backref=backref("supervisor", remote_side="Staff.id")
>> )
>>
>>
>> anchor_s = Staff.__table__.alias(name="anchor_s")
>> s = Staff.__table__.alias(name="s")
>> final_s = Staff.__table__.alias(name="final_s")
>>
>> recursive_cte = (
>> select(
>> [
>> anchor_s.c.id.label("anchor_id"),
>> anchor_s.c._enabling_factor,
>> anchor_s.c.selfreferencing_staff_id,
>> ]
>> ).select_from(anchor_s)
>> # this part we are going to move to the outside
>> # .where(anchor_s.c.id == Staff.id)
>> .cte(name="lineage_nodes", recursive=True)
>> )
>>
>> recursive_cte_a = recursive_cte.alias()
>>
>> lineage_nodes = recursive_cte.union_all(
>> select([s.c.id, s.c._enabling_factor, s.c.selfreferencing_staff_id])
>> .join(
>> recursive_cte_a, recursive_cte_a.c.selfreferencing_staff_id == s.c.id
>> )
>> .filter(recursive_cte_a.c._enabling_factor == None)
>> )
>>
>> top_id = (
>> select(func.min(lineage_nodes.c.anchor_id))
>> # here's where we moved it
>> .where(lineage_nodes.c.anchor_id == Staff.id)
>> .correlate(Staff)
>> .scalar_subquery()
>> )
>>
>>
>> Staff.effective_enabling_factor = column_property(
>> select(final_s.c._enabling_factor)
>> .where(final_s.c.record_id == top_id)
>> .scalar_subquery()
>> ) # This is where I define the desired column_property.
>>
>>
>> s = Session()
>>
>> q = s.query(Staff)
>> print(q)
>>
>> On Sun, Sep 26, 2021, at 2:56 AM, niuji...@gmail.com wrote:
>>>
>>> Hi Mike,
>>>
>>> Yes the SQL code runs as
Re: [sqlalchemy] recursive cte use current row as anchor
Hi Mike,
This code doesn't seem to yield desired result, now all the
`effective_enabling_factor` is `None`, except for those rows that carries a
`_enabling_factor` on itself. In other words, it doesn't seem to recusively
search the next immediately parent's marker at all.
And the SQL it generates is a little confusing, it seems to me that we
introduce a `recursive_cte_a` aliased table and gain nothing from it:
WITH RECURSIVE lineage_nodes(
anchor_id, _enabling_factor, selfreferencing_staff_id
) AS (
SELECT
anchor_f.id AS anchor_id,
anchor_f._enabling_factor AS _enabling_factor,
anchor_f.selfreferencing_staff_id AS selfreferencing_staff_id
FROM
staff AS anchor_f
UNION ALL
SELECT
anchor_f.id AS id,
anchor_f._enabling_factor AS _enabling_factor,
anchor_f.selfreferencing_staff_id AS selfreferencing_staff_id
FROM
staff AS anchor_f
JOIN lineage_nodes AS anon_2 ON anon_2.selfreferencing_staff_id =
anchor_f.id
WHERE
anon_2._enabling_factor IS NULL
)
SELECT
staff.id AS staff_id,
staff._enabling_factor AS staff__enabling_factor,
(
SELECT
final_f._enabling_factor
FROM
staff AS final_f
WHERE
final_f.id = (
SELECT
min(lineage_nodes.anchor_id) AS min_1
FROM
lineage_nodes
WHERE
lineage_nodes.anchor_id = staff.id
)
) AS anon_1
FROM
staff
On Sunday, September 26, 2021 at 7:35:20 AM UTC-7 Mike Bayer wrote:
> OK there's various small issues here but overall SQLAlchemy's new
> "nesting" feature does not seem to work correctly yet for a RECURSIVE CTE
> with UNION, meaning it's not very useful for RECURSIVE right now.
>
> But here's the thing, I'm not as SQL expert as some people think but I
> don't think it should be necessary for a CTE to actually be embedded in a
> subquery. You can keep the CTE on top, where it can more efficiently
> create a set of all rows, and then refer to it within a normal correlated
> subquery that's in the column_property().
>
> ive written the below MCVE we can work with going forward. see how close
> this is, but the goal is, keep the CTE on top as it normally can be and do
> correlations outside of it.
>
> from sqlalchemy import Column
> from sqlalchemy import ForeignKey
> from sqlalchemy import func
> from sqlalchemy import Integer
> from sqlalchemy import select
> from sqlalchemy.ext.declarative import declarative_base
> from sqlalchemy.orm import backref
> from sqlalchemy.orm import column_property
> from sqlalchemy.orm import relationship
> from sqlalchemy.orm import Session
>
> Base = declarative_base()
>
>
> class Staff(Base):
> __tablename__ = "staff"
>
> id = Column(Integer, primary_key=True)
>
> selfreferencing_staff_id = Column(
> Integer,
> ForeignKey("staff.id", onupdate="CASCADE", ondelete="SET NULL"),
> )
> _enabling_factor = Column(Integer)
> record_id = Column(Integer)
>
> team_members = relationship(
> "Staff", backref=backref("supervisor", remote_side="Staff.id")
> )
>
>
> anchor_s = Staff.__table__.alias(name="anchor_s")
> s = Staff.__table__.alias(name="s")
> final_s = Staff.__table__.alias(name="final_s")
>
> recursive_cte = (
> select(
> [
> anchor_s.c.id.label("anchor_id"),
> anchor_s.c._enabling_factor,
> anchor_s.c.selfreferencing_staff_id,
> ]
> ).select_from(anchor_s)
> # this part we are going to move to the outside
> # .where(anchor_s.c.id == Staff.id)
> .cte(name="lineage_nodes", recursive=True)
> )
>
> recursive_cte_a = recursive_cte.alias()
>
> lineage_nodes = recursive_cte.union_all(
> select([s.c.id, s.c._enabling_factor, s.c.selfreferencing_staff_id])
> .join(
> recursive_cte_a, recursive_cte_a.c.selfreferencing_staff_id ==
> s.c.id
> )
> .filter(recursive_cte_a.c._enabling_factor == None)
> )
>
> top_id = (
> select(func.min(lineage_nodes.c.anchor_id))
> # here's where we moved it
> .where(lineage_nodes.c.anchor_id == Staff.id)
> .correlate(Staff)
> .scalar_subquery()
> )
>
>
> Staff.effective_enabling_factor = column_property(
> select(final_s.c._enabling_factor)
> .where(final_s.c.record_id == top_id)
> .scalar_subquery()
> ) # This is where I define the desired column_property.
>
>
> s = Session()
>
> q = s.query(Staff)
> print(q)
>
> On Sun, Sep 26, 2021, at 2:56 AM, niuji...@gmail.com wrote:
>
>
> Hi Mike,
>
> Yes the SQL code runs as desired, but the Python code doesn't,
> unfortunately.
> After reading the references you pointed out, my Python code looks like
> this:
>
> class Staff(Base):
> id = Column(Integer, primary_key=True)
> selfreferencing_staff_id = Column(
> Integer,
> ForeignKey('staff_table.id',
>onupdate="CASCADE",
>ondelete='SET NULL'))
> _enabling_factor = Column(Integer)
>
Re: [sqlalchemy] recursive cte use current row as anchor
OK there's various small issues here but overall SQLAlchemy's new "nesting"
feature does not seem to work correctly yet for a RECURSIVE CTE with UNION,
meaning it's not very useful for RECURSIVE right now.
But here's the thing, I'm not as SQL expert as some people think but I don't
think it should be necessary for a CTE to actually be embedded in a subquery.
You can keep the CTE on top, where it can more efficiently create a set of all
rows, and then refer to it within a normal correlated subquery that's in the
column_property().
ive written the below MCVE we can work with going forward. see how close this
is, but the goal is, keep the CTE on top as it normally can be and do
correlations outside of it.
from sqlalchemy import Column
from sqlalchemy import ForeignKey
from sqlalchemy import func
from sqlalchemy import Integer
from sqlalchemy import select
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import backref
from sqlalchemy.orm import column_property
from sqlalchemy.orm import relationship
from sqlalchemy.orm import Session
Base = declarative_base()
class Staff(Base):
__tablename__ = "staff"
id = Column(Integer, primary_key=True)
selfreferencing_staff_id = Column(
Integer,
ForeignKey("staff.id", onupdate="CASCADE", ondelete="SET NULL"),
)
_enabling_factor = Column(Integer)
record_id = Column(Integer)
team_members = relationship(
"Staff", backref=backref("supervisor", remote_side="Staff.id")
)
anchor_s = Staff.__table__.alias(name="anchor_s")
s = Staff.__table__.alias(name="s")
final_s = Staff.__table__.alias(name="final_s")
recursive_cte = (
select(
[
anchor_s.c.id.label("anchor_id"),
anchor_s.c._enabling_factor,
anchor_s.c.selfreferencing_staff_id,
]
).select_from(anchor_s)
# this part we are going to move to the outside
# .where(anchor_s.c.id == Staff.id)
.cte(name="lineage_nodes", recursive=True)
)
recursive_cte_a = recursive_cte.alias()
lineage_nodes = recursive_cte.union_all(
select([s.c.id, s.c._enabling_factor, s.c.selfreferencing_staff_id])
.join(
recursive_cte_a, recursive_cte_a.c.selfreferencing_staff_id == s.c.id
)
.filter(recursive_cte_a.c._enabling_factor == None)
)
top_id = (
select(func.min(lineage_nodes.c.anchor_id))
# here's where we moved it
.where(lineage_nodes.c.anchor_id == Staff.id)
.correlate(Staff)
.scalar_subquery()
)
Staff.effective_enabling_factor = column_property(
select(final_s.c._enabling_factor)
.where(final_s.c.record_id == top_id)
.scalar_subquery()
) # This is where I define the desired column_property.
s = Session()
q = s.query(Staff)
print(q)
On Sun, Sep 26, 2021, at 2:56 AM, niuji...@gmail.com wrote:
>
> Hi Mike,
>
> Yes the SQL code runs as desired, but the Python code doesn't, unfortunately.
> After reading the references you pointed out, my Python code looks like this:
>
> class Staff(Base):
> id = Column(Integer, primary_key=True)
> selfreferencing_staff_id = Column(
> Integer,
> ForeignKey('staff_table.id',
>onupdate="CASCADE",
>ondelete='SET NULL'))
> _enabling_factor = Column(Integer)
>
>team_members = relationship('Staff',
>backref=backref(
>'supervisor',
>remote_side='Staff.id'))
>
> anchor_s = Staff.__table__.alias(name="anchor_s")
> s = Staff.__table__.alias(name="s")
> final_s = Staff.__table__.alias(name="final_s")
>
> recursive_cte = select([
> anchor_s.c.id, anchor_s.c._enabling_factor,
> anchor_s.c.selfreferencing_staff_id
>]).select_from(anchor_s).where(anchor_s.c.id == Staff.id).cte(
> name="lineage_nodes", recursive=True)
>
> lineage_nodes = recursive_cte.union_all(
>select([
> s.c.id, s.c._enabling_factor, s.c.selfreferencing_staff_id
> ]).join(recursive_cte, recursive_cte.c.selfreferencing_staff_id ==
> s.c.id).filter(recursive_cte.c._enabling_factor == None))
>
> top_id = select(sasql.func.min(lineage_nodes.c.id))
> Staff.effective_enabling_factor =
> column_property(select(final_s.c._enabling_factor).where(
> final_s.c.record_id == top_id).scalar_subquery()) # This is where I
> define the desired column_property.
>
>
>
>
> The problems seems to be that this code doesn't generate `correlated
> subquery` for each `Staff` row ( as in the SQL code `WHERE anchor_s.id =
> outer_s.id`). Could you take a look?
> On Saturday, September 25, 2021 at 8:26:46 PM UTC-7 Mike Bayer wrote:
>> __
>> well __class__.__table__ isn't going to be there inside the class body, just
>> to make things simple you will want to add this column_property() after the
>> Staff class is fully
Re: [sqlalchemy] recursive cte use current row as anchor
Hi Mike,
Yes the SQL code runs as desired, but the Python code doesn't,
unfortunately.
After reading the references you pointed out, my Python code looks like
this:
class Staff(Base):
id = Column(Integer, primary_key=True)
selfreferencing_staff_id = Column(
Integer,
ForeignKey('staff_table.id',
onupdate="CASCADE",
ondelete='SET NULL'))
_enabling_factor = Column(Integer)
team_members = relationship('Staff',
backref=backref(
'supervisor',
remote_side='Staff.id'))
anchor_s = Staff.__table__.alias(name="anchor_s")
s = Staff.__table__.alias(name="s")
final_s = Staff.__table__.alias(name="final_s")
recursive_cte = select([
anchor_s.c.id, anchor_s.c._enabling_factor,
anchor_s.c.selfreferencing_staff_id
]).select_from(anchor_s).where(anchor_s.c.id == Staff.id).cte(
name="lineage_nodes", recursive=True)
lineage_nodes = recursive_cte.union_all(
select([
s.c.id, s.c._enabling_factor, s.c.selfreferencing_staff_id
]).join(recursive_cte, recursive_cte.c.selfreferencing_staff_id
==
s.c.id).filter(recursive_cte.c._enabling_factor == None))
top_id = select(sasql.func.min(lineage_nodes.c.id))
Staff.effective_enabling_factor =
column_property(select(final_s.c._enabling_factor).where(
final_s.c.record_id == top_id).scalar_subquery()) # This is where
I define the desired column_property.
The problems seems to be that this code doesn't generate `correlated
subquery` for each `Staff` row ( as in the SQL code `WHERE anchor_s.id =
outer_s.id`). Could you take a look?
On Saturday, September 25, 2021 at 8:26:46 PM UTC-7 Mike Bayer wrote:
> well __class__.__table__ isn't going to be there inside the class body,
> just to make things simple you will want to add this column_property()
> after the Staff class is fully defined; then you make use of Staff. to
> get at columns.
> https://docs.sqlalchemy.org/en/14/orm/mapped_sql_expr.html#using-column-property
>
> will show how to assign a new column_property to the class after the fact.
>
> next, the query you have is correlating, but i really dont have any idea
> if SQLAlchemy is going to handle a correlated column deep inside of a CTE
> like that. The form you have, with the CTE embedded in the parenthesis,
> is only possible with the most recent SQLAlchemy 1.4.24 release where
> someone contributed a new parameter called "nesting", which means the CTE
> should not be moved to the top level of the SELECT. still, not really
> sure what a CTE will do inside a correlated subquery like that. For an
> example of how to use "nesting" see example four at
> https://docs.sqlalchemy.org/en/14/core/selectable.html?highlight=hascte#sqlalchemy.sql.expression.HasCTE.cte
>
> . for the correlate, when you write out the select() that refers to
> "outer_s", add .correlate(Staff) to it, which means Staff isn't added to
> the FROM list, it's assumed to be on the outside.
>
> give those a try but im not totally sure CTEs work as correlated
> subqueries right now, it's not been tried. I assume you've confirmed this
> query actually runs, im surprised you can even correlate inside of a CTE
> like that.
>
>
>
>
>
> On Sat, Sep 25, 2021, at 12:04 AM, niuji...@gmail.com wrote:
>
> Hi Mike, thanks for pointing out the direction.
> I've worked out the SQL, but failed when converting to SQLAlchemy
> construct.
>
> My SQL query looks like this:
>
> SELECT id, (
> WITH lineage_nodes (id, _enabling_factor,
> selfreferencing_staff_id) AS
> (
> SELECT anchor_s.id, anchor_s._enabling_factor,
> anchor_s.selfreferencing_staff_id
> FROM staff_table AS anchor_s
> WHERE anchor_s.id = outer_s.id
>
> UNION ALL
>
> SELECT s.id, s._enabling_factor, s.selfreferencing_staff_id
> FROM lineage_nodes AS l
> INNER JOIN staff_table AS s
> ON l.selfreferencing_staff_id = s.id
> WHERE l._enabling_factor IS NULL
> ),
>
> top_node_id (top_id) AS
> (
> SELECT MIN(id) AS top_id FROM lineage_nodes
> )
>
> SELECT staff_table._enabling_factor
> FROM staff_table
> INNER JOIN top_node_id
> ON staff_table.id = top_node_id.top_id
> ) AS effective_enabling_factor
> FROM staff_table AS outer_s;
>
>
>
>
> My Python codes looks like this:
>
>
> class Staff(Base):
> id = Column(Integer, primary_key=True)
> selfreferencing_staff_id = Column(
> Integer,
> ForeignKey('staff_table.id',
>onupdate="CASCADE",
>ondelete='SET NULL'))
>
Re: [sqlalchemy] recursive cte use current row as anchor
well __class__.__table__ isn't going to be there inside the class body, just to
make things simple you will want to add this column_property() after the Staff
class is fully defined; then you make use of Staff. to get at columns.
https://docs.sqlalchemy.org/en/14/orm/mapped_sql_expr.html#using-column-property
will show how to assign a new column_property to the class after the fact.
next, the query you have is correlating, but i really dont have any idea if
SQLAlchemy is going to handle a correlated column deep inside of a CTE like
that. The form you have, with the CTE embedded in the parenthesis, is only
possible with the most recent SQLAlchemy 1.4.24 release where someone
contributed a new parameter called "nesting", which means the CTE should not be
moved to the top level of the SELECT. still, not really sure what a CTE will
do inside a correlated subquery like that. For an example of how to use
"nesting" see example four at
https://docs.sqlalchemy.org/en/14/core/selectable.html?highlight=hascte#sqlalchemy.sql.expression.HasCTE.cte
. for the correlate, when you write out the select() that refers to
"outer_s", add .correlate(Staff) to it, which means Staff isn't added to the
FROM list, it's assumed to be on the outside.
give those a try but im not totally sure CTEs work as correlated subqueries
right now, it's not been tried. I assume you've confirmed this query actually
runs, im surprised you can even correlate inside of a CTE like that.
On Sat, Sep 25, 2021, at 12:04 AM, niuji...@gmail.com wrote:
> Hi Mike, thanks for pointing out the direction.
> I've worked out the SQL, but failed when converting to SQLAlchemy construct.
>
> My SQL query looks like this:
>
> SELECT id, (
> WITH lineage_nodes (id, _enabling_factor, selfreferencing_staff_id) AS
> (
> SELECT anchor_s.id, anchor_s._enabling_factor,
> anchor_s.selfreferencing_staff_id
> FROM staff_table AS anchor_s
> WHERE anchor_s.id = outer_s.id
>
> UNION ALL
>
> SELECT s.id, s._enabling_factor, s.selfreferencing_staff_id
> FROM lineage_nodes AS l
> INNER JOIN staff_table AS s
> ON l.selfreferencing_staff_id = s.id
> WHERE l._enabling_factor IS NULL
> ),
>
> top_node_id (top_id) AS
> (
> SELECT MIN(id) AS top_id FROM lineage_nodes
> )
>
> SELECT staff_table._enabling_factor
> FROM staff_table
> INNER JOIN top_node_id
> ON staff_table.id = top_node_id.top_id
> ) AS effective_enabling_factor
> FROM staff_table AS outer_s;
>
>
>
>
> My Python codes looks like this:
>
>
> class Staff(Base):
> id = Column(Integer, primary_key=True)
> selfreferencing_staff_id = Column(
> Integer,
> ForeignKey('staff_table.id',
>onupdate="CASCADE",
>ondelete='SET NULL'))
> _enabling_factor = Column(Integer)
>
> ## codes below doesn't work:
> anchor_s = __class__.__table__.alias(name="anchor_s")
> s = __class__.__table__.alias(name="s")
>
>recursive_cte = select([
> id, _enabling_factor, selfreferencing_staff_id
>]).select_from(anchor_s).where(anchor_s.c.id == id).cte(
> name="lineage_nodes", recursive=True)
>
>lineage_nodes = recursive_cte.union_all(
>select([
> s.c.id, s.c._enabling_factor, s.c.selfreferencing_staff_id
> ]).join(recursive_cte, recursive_cte.c.selfreferencing_staff_id ==
> s.c.id).filter(recursive_cte.c._enabling_factor == None))
>
>top_id = select(sasql.func.min(lineage_nodes.c.id))
>effective_enabling_factor = column_property(...) # I have trouble in
> this line here.
>## codes above has a NameError: name '__class__' is not defined
>
>team_members = relationship('Staff',
>backref=backref(
>'supervisor',
>remote_side='Staff.id'))
> On Friday, September 24, 2021 at 1:00:01 PM UTC-7 Mike Bayer wrote:
>> __
>> this is a hefty query to dig in to but column_property() subqueries have to
>> be formed in terms of a correlated subquery. So instead of injecting a
>> particular primary key into it, you set it to point to the Staff.id column.
>>
>> correlated subqueries are not terrific performers and the construct can be a
>> little bit clumsy in the ORM as well, however, the second example at
>> https://docs.sqlalchemy.org/en/14/orm/mapped_sql_expr.html#using-column-property
>> shows the general idea.
>>
>> a first step to understanding might be to write out the SQL you think you
>> want when you SELECT some Staff rows, where one of the columns in the row is
>> the "effective_enabling_factor".
Re: [sqlalchemy] recursive cte use current row as anchor
Hi Mike, thanks for pointing out the direction.
I've worked out the SQL, but failed when converting to SQLAlchemy construct.
My SQL query looks like this:
SELECT id, (
WITH lineage_nodes (id, _enabling_factor, selfreferencing_staff_id)
AS
(
SELECT anchor_s.id, anchor_s._enabling_factor,
anchor_s.selfreferencing_staff_id
FROM staff_table AS anchor_s
WHERE anchor_s.id = outer_s.id
UNION ALL
SELECT s.id, s._enabling_factor, s.selfreferencing_staff_id
FROM lineage_nodes AS l
INNER JOIN staff_table AS s
ON l.selfreferencing_staff_id = s.id
WHERE l._enabling_factor IS NULL
),
top_node_id (top_id) AS
(
SELECT MIN(id) AS top_id FROM lineage_nodes
)
SELECT staff_table._enabling_factor
FROM staff_table
INNER JOIN top_node_id
ON staff_table.id = top_node_id.top_id
) AS effective_enabling_factor
FROM staff_table AS outer_s;
My Python codes looks like this:
class Staff(Base):
id = Column(Integer, primary_key=True)
selfreferencing_staff_id = Column(
Integer,
ForeignKey('staff_table.id',
onupdate="CASCADE",
ondelete='SET NULL'))
_enabling_factor = Column(Integer)
## codes below doesn't work:
anchor_s = __class__.__table__.alias(name="anchor_s")
s = __class__.__table__.alias(name="s")
recursive_cte = select([
id, _enabling_factor, selfreferencing_staff_id
]).select_from(anchor_s).where(anchor_s.c.id == id).cte(
name="lineage_nodes", recursive=True)
lineage_nodes = recursive_cte.union_all(
select([
s.c.id, s.c._enabling_factor, s.c.selfreferencing_staff_id
]).join(recursive_cte, recursive_cte.c.selfreferencing_staff_id
==
s.c.id).filter(recursive_cte.c._enabling_factor == None))
top_id = select(sasql.func.min(lineage_nodes.c.id))
effective_enabling_factor = column_property(...) # I have trouble in
this line here.
## codes above has a NameError: name '__class__' is not defined
team_members = relationship('Staff',
backref=backref(
'supervisor',
remote_side='Staff.id'))
On Friday, September 24, 2021 at 1:00:01 PM UTC-7 Mike Bayer wrote:
> this is a hefty query to dig in to but column_property() subqueries have
> to be formed in terms of a correlated subquery. So instead of injecting a
> particular primary key into it, you set it to point to the Staff.id column.
>
> correlated subqueries are not terrific performers and the construct can be
> a little bit clumsy in the ORM as well, however, the second example at
> https://docs.sqlalchemy.org/en/14/orm/mapped_sql_expr.html#using-column-property
>
> shows the general idea.
>
> a first step to understanding might be to write out the SQL you think you
> want when you SELECT some Staff rows, where one of the columns in the row
> is the "effective_enabling_factor". that column needs to be written as a
> correlated subquery for it to be compatible with column_property().
>
>
>
> On Fri, Sep 24, 2021, at 1:47 AM, niuji...@gmail.com wrote:
>
> class Staff(Base):
> id = Column(Integer, primary_key=True)
> selfreferencing_staff_id = Column(
> Integer,
> ForeignKey('staff_table.id',
>onupdate="CASCADE",
>ondelete='SET NULL'))
> _enabling_factor = Column(Integer)
> effective_enabling_factor = column_property(...) # I have trouble in
> this line here.
> team_members = relationship('Staff',
>backref=backref(
>'supervisor',
>remote_side='Staff.id'))
>
>
> This is a self-referencing lineage. Each staff has one supervisor above
> them. Each staff has a `_enabling_factor`, which can be either a Integer,
> or Null. A staff's `effective_enabling_factor` is either their own
> `_enabling_factor` value, or their supervisor's `effective_enabling_factor`
> if their own is Null.
>
> This seems to be a case to use recursive CTE.
> I can construct the query for a certain staff member, e.g. staff #5:
>
> recursive_cte = select([Staff.id, Staff._enabling_factor,
> Staff.selfreferencing_staff_id]).where(Staff.id==5).cte(recursive=True)
>
> lineage_nodes = recursive_cte.union_all(select([Staff.id,
> Staff._enabling_factor,
> Staff.selfreferencing_staff_id]).join(recursive_cte,
> recursive_cte.c.selfreferencing_staff_id==Staff.record_id).filter(recursive_cte.c._enabling_factor
>
> == None))
>
> marker_carrying_supervisor_id = select(sasql.func.min(lineage_nodes.c.id
>
Re: [sqlalchemy] recursive cte use current row as anchor
this is a hefty query to dig in to but column_property() subqueries have to be
formed in terms of a correlated subquery. So instead of injecting a particular
primary key into it, you set it to point to the Staff.id column.
correlated subqueries are not terrific performers and the construct can be a
little bit clumsy in the ORM as well, however, the second example at
https://docs.sqlalchemy.org/en/14/orm/mapped_sql_expr.html#using-column-property
shows the general idea.
a first step to understanding might be to write out the SQL you think you want
when you SELECT some Staff rows, where one of the columns in the row is the
"effective_enabling_factor". that column needs to be written as a correlated
subquery for it to be compatible with column_property().
On Fri, Sep 24, 2021, at 1:47 AM, niuji...@gmail.com wrote:
> class Staff(Base):
> id = Column(Integer, primary_key=True)
> selfreferencing_staff_id = Column(
> Integer,
> ForeignKey('staff_table.id',
>onupdate="CASCADE",
>ondelete='SET NULL'))
> _enabling_factor = Column(Integer)
> effective_enabling_factor = column_property(...) # I have trouble in
> this line here.
> team_members = relationship('Staff',
>backref=backref(
>'supervisor',
>remote_side='Staff.id'))
>
>
> This is a self-referencing lineage. Each staff has one supervisor above them.
> Each staff has a `_enabling_factor`, which can be either a Integer, or Null.
> A staff's `effective_enabling_factor` is either their own `_enabling_factor`
> value, or their supervisor's `effective_enabling_factor` if their own is Null.
>
> This seems to be a case to use recursive CTE.
> I can construct the query for a certain staff member, e.g. staff #5:
>
> recursive_cte = select([Staff.id, Staff._enabling_factor,
> Staff.selfreferencing_staff_id]).where(Staff.id==5).cte(recursive=True)
>
> lineage_nodes = recursive_cte.union_all(select([Staff.id,
> Staff._enabling_factor, Staff.selfreferencing_staff_id]).join(recursive_cte,
> recursive_cte.c.selfreferencing_staff_id==Staff.record_id).filter(recursive_cte.c._enabling_factor
> == None))
>
> marker_carrying_supervisor_id =
> select(sasql.func.min(lineage_nodes.c.id)).scalar_subquery()
>
> select(Staff._enabling_factor).where(Staff.id==marker_carrying_supervisor_id)
>
>
> However, I don't see how I can write this recursive CTE as a column_property
> on the `Staff` class. Instead of giving specific primary key (e.g. #5), I
> need to somehow reference current row as the anchor.
>
> How to solve this?
>
>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
>
> To post example code, please provide an MCVE: Minimal, Complete, and
> Verifiable Example. See http://stackoverflow.com/help/mcve for a full
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>
> .
--
SQLAlchemy -
The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
To post example code, please provide an MCVE: Minimal, Complete, and Verifiable
Example. See http://stackoverflow.com/help/mcve for a full description.
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