This Worked!
@compiles(BinaryExpression, 'ibm_db_sa')
def _comp_binary(element, compiler, **kwargs):
text = compiler.visit_binary(element, **kwargs)
if element.operator is operators.in_op:
text = re.sub(r"\) IN \(", ") IN (VALUES ", text)
return text
Had to make a couple of changes.... 1) the dialect name is 'ibm_db_sa' and
2) (strangely!) DB2 gave me an error that it explicitly disallows parameter
markers in VALUES (but only in the single-column-key case). My other tests
seem to indicate that this was a misleading error message but I'm not going
to touch it again now that it is working.
Thanks!
On Thursday, 27 June 2019 15:03:01 UTC-4, Mike Bayer wrote:
>
>
>
> On Thu, Jun 27, 2019, at 2:11 PM, Steven James wrote:
>
> Currently, `selectin` loading with composite keys works for me on MySQL
> and SQLite. The documentation states that it also works with Postgres. I'm
> currently trying to get it working on DB2 (connecting to a DB2 for i, 7.2
> system.
>
> (the following assumes a table with the primary key consisting of two
> columns: a and b)
>
> selectin loading currently emits:
> `SELECT * FROM table WHERE (table.a, table.b) IN ((?, ?), (?, ?))`
>
> For this type of loading to work in DB2 (DB2 for i), the syntax needs to
> be:
> `SELECT * FROM table WHERE (table.a, table.b) IN VALUES (?, ?), (?,?)`
>
> Is there any way to implement this without a core change? I'm wondering if
> I can override the normal operation of in_() using a custom dialect or
> custom default comparator.
>
>
> funny thing is that I'm a Red Hat employee, so assuming RH's merger with
> IBM goes through I may eventually be an IBM employee, and maybe they'd like
> to give me DB2 things to work on :) However, that is not the case right
> now and I've done only very limited work with the DB2 driver as I'm sure
> you're aware the database itself is a beast.
>
> So this is something DB2's SQLAlchemy driver will have to add support for
> at some point, the selectinload thing is going to become more popular and
> also the internal mechanism for "IN" is going to be moving entirely to a
> newer architecture called "expanding". That's probably not important here
> though.
>
> For now, in order to get that "VALUES" in there, you don't need to
> "change" Core or work with custom datatypes, there's a variety of event
> hooks that can give you access to that part of the SQL more at the string
> level. I'm able to make this work also on Postgresql by intercepting
> BinaryExpression in the compiler, see the example below.
>
> import re
>
> from sqlalchemy import Column
> from sqlalchemy import create_engine
> from sqlalchemy import ForeignKeyConstraint
> from sqlalchemy import Integer
> from sqlalchemy import String
> from sqlalchemy.ext.compiler import compiles
> from sqlalchemy.ext.declarative import declarative_base
> from sqlalchemy.orm import relationship
> from sqlalchemy.orm import selectinload
> from sqlalchemy.orm import Session
> from sqlalchemy.sql import operators
> from sqlalchemy.sql.expression import BinaryExpression
>
>
> @compiles(BinaryExpression, "postgresql") # because I'm testing it here
> @compiles(BinaryExpression, "db2")
> def _comp_binary(element, compiler, **kw):
> text = compiler.visit_binary(element, **kw)
> if element.operator is operators.in_op:
> text = re.sub(r" IN \(", " IN (VALUES ", text)
> return text
>
>
> Base = declarative_base()
>
>
> class A(Base):
> __tablename__ = "a"
>
> id = Column(Integer, primary_key=True)
> id2 = Column(Integer, primary_key=True)
> data = Column(String)
>
> bs = relationship("B")
>
>
> class B(Base):
> __tablename__ = "b"
> id = Column(Integer, primary_key=True)
>
> a_id = Column(Integer)
> a_id2 = Column(Integer)
>
> __table_args__ = (
> ForeignKeyConstraint(["a_id", "a_id2"], ["a.id", "a.id2"]),
> )
>
>
> e = create_engine("postgresql://scott:tiger@localhost/test", echo=True)
> Base.metadata.drop_all(e)
> Base.metadata.create_all(e)
>
> s = Session(e)
>
> s.add(A(id=1, id2=1, bs=[B(), B()]))
> s.commit()
>
> s.query(A).options(selectinload(A.bs)).all()
>
>
>
>
>
>
> Thanks,
> Steven James
>
>
> --
> 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 sqlal...@googlegroups.com <javascript:>.
> To post to this group, send email to sqlal...@googlegroups.com
> <javascript:>.
> Visit this group at https://groups.google.com/group/sqlalchemy.
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/sqlalchemy/e7a3b368-d40e-4aba-84d5-10020fb05fe4%40googlegroups.com
>
> <https://groups.google.com/d/msgid/sqlalchemy/e7a3b368-d40e-4aba-84d5-10020fb05fe4%40googlegroups.com?utm_medium=email&utm_source=footer>
> .
> For more options, visit https://groups.google.com/d/optout.
>
>
>
--
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 post to this group, send email to sqlalchemy@googlegroups.com.
Visit this group at https://groups.google.com/group/sqlalchemy.
To view this discussion on the web visit
https://groups.google.com/d/msgid/sqlalchemy/7f6bab32-5717-4fac-bb10-d5b2ee1610dc%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
