On Wed, Jul 12, 2017 at 4:54 PM, <yoch.me...@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/
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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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