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. >>> --- >>> You received this message because you are subscribed to the Google Groups >>> "sqlalchemy" group. >>> To unsubscribe from this group and stop receiving emails from it, send an >>> email to sqlalchemy+...@googlegroups.com. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/sqlalchemy/a5e26719-3e5e-4f6e-92fc-c3319ad3ec6fn%40googlegroups.com >>> >>> <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. > --- > You received this message because you are subscribed to the Google Groups > "sqlalchemy" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to sqlalchemy+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/sqlalchemy/62f2501c-ce1a-43bb-859f-dc4ff8019c3bn%40googlegroups.com > > <https://groups.google.com/d/msgid/sqlalchemy/62f2501c-ce1a-43bb-859f-dc4ff8019c3bn%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. --- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. 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