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 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.<col>
>>>> 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". 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
>>>>>>> description.
>>>>>>> ---
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>>>>>>>
>>>>>>> <https://groups.google.com/d/msgid/sqlalchemy/a5e26719-3e5e-4f6e-92fc-c3319ad3ec6fn%40googlegroups.com?utm_medium=email&utm_source=footer>.
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> 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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>>>>>
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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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>>
>
>
> --
> 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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http://www.sqlalchemy.org/
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