this is how that would have to be mapped, hypothetically:
class EngineerBase(Person):
__tablename__ = 'engineer'
id = Column(ForeignKey('person.id'), primary_key=True)
engineer_name = Column(String(30))
__mapper_args__ = {
'polymorphic_load': 'selectin'
}
class EngineerType1(EngineerBase):
__mapper_args__ = {
'polymorphic_identity': 'engineer_t1',
'polymorphic_load': 'inline'
}
class EngineerType2(EngineerBase):
__mapper_args__ = {
'polymorphic_identity': 'engineer_t2',
'polymorphic_load': 'inline'
}
doesn't work of course since the polymorphic selectin load is a new
feature trying to work its way into a very intricate workflow. I
threw up
https://bitbucket.org/zzzeek/sqlalchemy/issues/4026/mixing-selectin-load-on-top-of-inline
to look into it. not sure how easy / hard it would be.
On Wed, Jul 12, 2017 at 7:09 PM, <yoch.me...@gmail.com> wrote:
> Here a MCWE :
>
> from sqlalchemy import Table, Column, Integer, String, ForeignKey,
> create_engine
> from sqlalchemy.orm import Session
> from sqlalchemy.ext.declarative import declarative_base
>
>
> Base = declarative_base()
>
>
> class Person(Base):
> __tablename__ = 'person'
>
> id = Column(Integer, primary_key=True)
> type = Column(String(50), nullable=False)
> name = Column(String(50))
>
> __mapper_args__ = {
> 'polymorphic_identity': 'person',
> 'polymorphic_on': type
> }
>
>
> class Manager(Person):
> __tablename__ = 'manager'
>
> id = Column(ForeignKey('person.id'), primary_key=True)
> manager_name = Column(String(30))
>
> __mapper_args__ = {
> 'polymorphic_identity': 'manager',
> 'polymorphic_load': 'selectin'
> }
>
>
> class EngineerBase(Person):
> __tablename__ = 'engineer'
>
> id = Column(ForeignKey('person.id'), primary_key=True)
> engineer_name = Column(String(30))
>
>
> class EngineerType1(EngineerBase):
> __mapper_args__ = {
> 'polymorphic_identity': 'engineer_t1',
> 'polymorphic_load': 'selectin'
> }
>
>
> class EngineerType2(EngineerBase):
> __mapper_args__ = {
> 'polymorphic_identity': 'engineer_t2',
> 'polymorphic_load': 'selectin'
> }
>
>
> engine = create_engine('sqlite://')
> Base.metadata.create_all(engine)
>
> engine.echo = True
>
> session = Session(engine)
>
> eng1 = EngineerType1()
> eng2 = EngineerType2()
>
> session.add_all([eng1, eng2])
> session.commit()
>
> session.query(Person).all()
>
> produces the following three queries :
>
> 2017-07-13 00:59:07,243 INFO sqlalchemy.engine.base.Engine SELECT person.id
> AS person_id, person.type AS person_type, person.name AS person_name
> FROM person
> 2017-07-13 00:59:07,243 INFO sqlalchemy.engine.base.Engine ()
> 2017-07-13 00:59:07,248 INFO sqlalchemy.engine.base.Engine SELECT
> engineer.id AS engineer_id, person.id AS person_id, person.type AS
> person_type
> FROM person JOIN engineer ON person.id = engineer.id
> WHERE person.id IN (?) AND person.type IN (?) ORDER BY person.id
> 2017-07-13 00:59:07,249 INFO sqlalchemy.engine.base.Engine (2,
> 'engineer_t2')
> 2017-07-13 00:59:07,253 INFO sqlalchemy.engine.base.Engine SELECT
> engineer.id AS engineer_id, person.id AS person_id, person.type AS
> person_type
> FROM person JOIN engineer ON person.id = engineer.id
> WHERE person.id IN (?) AND person.type IN (?) ORDER BY person.id
> 2017-07-13 00:59:07,254 INFO sqlalchemy.engine.base.Engine (1,
> 'engineer_t1')
>
> The last two queries can be grouped together.
>
> Le jeudi 13 juillet 2017 01:45:46 UTC+3, yoch....@gmail.com a écrit :
>>
>> I have a mixed configuration with both joined and single table subclasses
>> in a two-levels inheritance (like that), so selectin seems to be the right
>> choice for me.
>>
>> Le jeudi 13 juillet 2017 01:09:50 UTC+3, Mike Bayer a écrit :
>>>
>>> On Wed, Jul 12, 2017 at 4:54 PM, <yoch....@gmail.com> wrote:
>>> > I noticed that {'polymorphic_load': 'selectin'} on single table
>>> > inheritance
>>> > can make several SQL queries unnecessarily.
>>>
>>> well "selectin" loading would be inappropriate for single table
>>> inheritance because you are telling it to emit additional queries for
>>> additional subclasses, when in reality you'd like the original query
>>> just to include all columns. For this reason the traditional
>>> "with_polymorphic" approach is more appropriate for eager loading of
>>> single table subclasses.
>>>
>>>
>>> >
>>> >
>>> > Le mercredi 12 juillet 2017 22:02:04 UTC+3, yoch....@gmail.com a écrit
>>> > :
>>> >>
>>> >> Very awaited version for me (because the selectin) !
>>> >>
>>> >> I tested in my code both the eagerload and the polymorphic usages, and
>>> >> everything works perfectly.
>>> >>
>>> >> Thank you Mike
>>> >>
>>> >> Le lundi 10 juillet 2017 16:44:03 UTC+3, Mike Bayer a écrit :
>>> >>>
>>> >>> SQLAlchemy release 1.2.0b1 is now available.
>>> >>>
>>> >>> This is the first beta for the 1.2 series of SQLAlchemy. As is always
>>> >>> the case for beta releases, the release is available on Pypi, but
>>> >>> only
>>> >>> installable when specifying the --pre flag with pip.
>>> >>>
>>> >>> Key highlights of version 1.2 include:
>>> >>>
>>> >>> * Connection pool pre-ping - The connection pool now includes an
>>> >>> optional "pre ping" feature that will test the "liveness" of a pooled
>>> >>> connection for every connection checkout, transparently recycling the
>>> >>> DBAPI connection if the database is disconnected. This feature
>>> >>> eliminates the need for the "pool recycle" flag as well as the issue
>>> >>> of errors raised when a pooled connection is used after a database
>>> >>> restart.
>>> >>>
>>> >>> * New eagerloading features - an all-new eager loader called
>>> >>> "selectin" is added. This loader is similar to "subquery" eager
>>> >>> loading, but foregoes embedding a complex subquery in favor of using
>>> >>> a
>>> >>> simple IN expression which uses the primary key values of the
>>> >>> just-loaded objects to locate related rows. This style of loading
>>> >>> will
>>> >>> perform dramatically better than "subquery" eager loading in many
>>> >>> cases.
>>> >>>
>>> >>> * New polymorphic loading options - A new "selectin" loader is also
>>> >>> implemented for polymorphic inheritance hierarchies, which will load
>>> >>> the extra table rows for subclasses in a result set all at once,
>>> >>> without the need to use JOIN or "with_polymorphic". New declarative
>>> >>> options are added to allow per-subclass polymorphic loading
>>> >>> configuration as well.
>>> >>>
>>> >>> * The IN operator now emits a simple expression for empty IN - The
>>> >>> long standing behavior of "empty in" resolving to a non-performant
>>> >>> expression with a warning has been removed as default behavior; for
>>> >>> an
>>> >>> IN with no elements, a simple 1 != 1 expression is now used to
>>> >>> evaluate to "false".
>>> >>>
>>> >>> * INSERT..ON DUPLICATE KEY UPDATE support in MySQL - complementing
>>> >>> the
>>> >>> support for PostgreSQL "INSERT..ON CONFLICT" in 1.1, the MySQL
>>> >>> dialect
>>> >>> now supports the ON DUPLICATE KEY phrase. Simple database-agnostic
>>> >>> "merge" routines can now be composed against these two backends.
>>> >>>
>>> >>> * COMMENT Support - thanks to a generous contribution, version 1.2
>>> >>> can
>>> >>> emit all necessary DDL as well as fully reflect SQL comments for
>>> >>> tables and columns against the MySQL, PostgreSQL, and Oracle
>>> >>> backends.
>>> >>>
>>> >>> * SQL expression caching within ORM loaders - the "lazyload" feature
>>> >>> as well as the new "selectin" loading now use SQL expression caching
>>> >>> using the "baked query" extension when emitting queries, removing a
>>> >>> significant bulk of Python overhead from these very common
>>> >>> operations.
>>> >>>
>>> >>> Users should carefully review the "What's New in SQLAlchemy 1.2?
>>> >>> document" [1] as well as the Changelog [2] to note which behaviors
>>> >>> and
>>> >>> issues are affected. We'd like to thank the many contributors who
>>> >>> helped with this release.
>>> >>>
>>> >>> SQLAlchemy 1.2.0b1 is available on the Download Page [3].
>>> >>>
>>> >>> [1] http://docs.sqlalchemy.org/en/latest/changelog/migration_12.html
>>> >>> [2] http://www.sqlalchemy.org/changelog/CHANGES_1_2_0b1
>>> >>> [3] http://www.sqlalchemy.org/download.html
>>> >
>>> > --
>>> > 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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--
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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