Re: [sqlalchemy] Mixins and lazy (query) attributes
Il giorno mercoledì 5 giugno 2019 18:17:48 UTC+2, Mike Bayer ha scritto:
>
>
>
> On Wed, Jun 5, 2019, at 12:02 PM, Christian Barra wrote:
>
> Hi, I am trying to understand what the best approach is to have lazy
> attributes defined on a mixin and then used them on the subclasses.
>
> Ideally I'd would like to defer the load of that attribute (controller)
> and use `undefer` when I know that that attribute is needed, to execute
> only one query.
>
> Below there's the code I am trying to use, `recipe_set` is a backref, same
> for `unit`, Controller is another model.
>
>
> class BaseRecipeMixin(APIResourceMixin):
> _key = None
>
> @declared_attr
> def recipe_set_id(self):
> return db.Column(db.ForeignKey('recipe_set.id'), unique=True,
> nullable=False)
>
> @property
> def controller(self):
> return column_property(
> Controller.query.filter(
> Controller.unit == self.recipe_set.unit,
> Controller.is_master.is_(True),
> Controller.is_deleted.is_(False),
> ).one_or_none(),
> deferred=True,
> )
>
>
> class EcRecipe(DosingRecipeMixin, BaseRecipeMixin, UpdateMixin, db.Model):
> id = db.Column(db.Integer, primary_key=True)
> pump_time = db.Column(db.Float, nullable=False, default=8)
>
>
> But when I try to run this
>
>
>
> when you declare mapped attributes on a mixin you have to use
> @declared_attr:
>
>
> https://docs.sqlalchemy.org/en/13/orm/extensions/declarative/mixins.html#mixing-in-deferred-column-property-and-other-mapperproperty-classes
>
> The column_property() object needs to be made part of the mapping and
> declarative uses this decorator to know it has to do that.
>
>
>
Thanks Mike, I'll try to use @declared_attr and go through the link.
--
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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Re: [sqlalchemy] Mixins and lazy (query) attributes
On Wed, Jun 5, 2019, at 12:02 PM, Christian Barra wrote:
> Hi, I am trying to understand what the best approach is to have lazy
> attributes defined on a mixin and then used them on the subclasses.
>
> Ideally I'd would like to defer the load of that attribute (controller) and
> use `undefer` when I know that that attribute is needed, to execute only one
> query.
>
> Below there's the code I am trying to use, `recipe_set` is a backref, same
> for `unit`, Controller is another model.
>
>
> class BaseRecipeMixin(APIResourceMixin):
> _key = None
>
> @declared_attr
> def recipe_set_id(self):
> return db.Column(db.ForeignKey('recipe_set.id'), unique=True, nullable=False)
>
> @property
> def controller(self):
> return column_property(
> Controller.query.filter(
> Controller.unit == self.recipe_set.unit,
> Controller.is_master.is_(True),
> Controller.is_deleted.is_(False),
> ).one_or_none(),
> deferred=True,
> )
>
>
> class EcRecipe(DosingRecipeMixin, BaseRecipeMixin, UpdateMixin, db.Model):
> id = db.Column(db.Integer, primary_key=True)
> pump_time = db.Column(db.Float, nullable=False, default=8)
>
>
> But when I try to run this
when you declare mapped attributes on a mixin you have to use @declared_attr:
https://docs.sqlalchemy.org/en/13/orm/extensions/declarative/mixins.html#mixing-in-deferred-column-property-and-other-mapperproperty-classes
The column_property() object needs to be made part of the mapping and
declarative uses this decorator to know it has to do that.
>
>
> models.EcRecipe.query.first().controller
>
>
> I get this error
>
> Traceback (most recent call last):
> File
> "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/code.py",
> line 90, in runcode
> exec(code, self.locals)
> File "", line 1, in
> File "/Users/cbarra/Projects/kompost/recipes/models.py", line 262, in
> controller
> deferred=True,
> File "", line 2, in column_property
> File "", line 2, in __init__
> File
> "/Users/cbarra/Projects/.venv/lib/python3.7/site-packages/sqlalchemy/util/deprecations.py",
> line 130, in warned
> return fn(*args, **kwargs)
> File
> "/Users/cbarra/Projects/.venv/lib/python3.7/site-packages/sqlalchemy/orm/properties.py",
> line 134, in __init__
> self._orig_columns = [expression._labeled(c) for c in columns]
> File
> "/Users/cbarra/Projects/.venv/lib/python3.7/site-packages/sqlalchemy/orm/properties.py",
> line 134, in
> self._orig_columns = [expression._labeled(c) for c in columns]
> File "", line 1, in
> File
> "/Users/cbarra/Projects/.venv/lib/python3.7/site-packages/sqlalchemy/sql/elements.py",
> line 4373, in _labeled
> return element.label(None)
> AttributeError: 'NoneType' object has no attribute 'label'
>
>
> while when I try to use `undefer` with
>
>
> models.EcRecipe.query.options(orm.undefer('controller'))
>
>
> the error is different
>
> Traceback (most recent call last):
> File
> "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/code.py",
> line 90, in runcode
> exec(code, self.locals)
> File "", line 1, in
> File
> "/Users/cbarra/Projects/.venv/lib/python3.7/site-packages/sqlalchemy/orm/query.py",
> line 1523, in options
> return self._options(False, *args)
> File "", line 2, in _options
> File
> "/Users/cbarra/Projects/.venv/lib/python3.7/site-packages/sqlalchemy/orm/base.py",
> line 220, in generate
> fn(self, *args[1:], **kw)
> File
> "/Users/cbarra/Projects/.venv/lib/python3.7/site-packages/sqlalchemy/orm/query.py",
> line 1542, in _options
> opt.process_query(self)
> File
> "/Users/cbarra/Projects/.venv/lib/python3.7/site-packages/sqlalchemy/orm/strategy_options.py",
> line 168, in process_query
> self._process(query, True)
> File
> "/Users/cbarra/Projects/.venv/lib/python3.7/site-packages/sqlalchemy/orm/strategy_options.py",
> line 542, in _process
> raiseerr,
> File
> "/Users/cbarra/Projects/.venv/lib/python3.7/site-packages/sqlalchemy/orm/strategy_options.py",
> line 720, in _bind_loader
> raiseerr,
> File
> "/Users/cbarra/Projects/.venv/lib/python3.7/site-packages/sqlalchemy/orm/strategy_options.py",
> line 235, in _generate_path
> attr = found_property = attr.property
> AttributeError: 'property' object has no attribute 'property'
>
> I am bit puzzled between property, hybrid_property and column_property, what
> is the best way to have lazy attributes defined on a mixin?
>
> --
> 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
[sqlalchemy] Mixins and lazy (query) attributes
Hi, I am trying to understand what the best approach is to have lazy
attributes defined on a mixin and then used them on the subclasses.
Ideally I'd would like to defer the load of that attribute (controller) and
use `undefer` when I know that that attribute is needed, to execute only
one query.
Below there's the code I am trying to use, `recipe_set` is a backref, same
for `unit`, Controller is another model.
class BaseRecipeMixin(APIResourceMixin):
_key = None
@declared_attr
def recipe_set_id(self):
return db.Column(db.ForeignKey('recipe_set.id'), unique=True,
nullable=False)
@property
def controller(self):
return column_property(
Controller.query.filter(
Controller.unit == self.recipe_set.unit,
Controller.is_master.is_(True),
Controller.is_deleted.is_(False),
).one_or_none(),
deferred=True,
)
class EcRecipe(DosingRecipeMixin, BaseRecipeMixin, UpdateMixin, db.Model):
id = db.Column(db.Integer, primary_key=True)
pump_time = db.Column(db.Float, nullable=False, default=8)
But when I try to run this
models.EcRecipe.query.first().controller
I get this error
Traceback (most recent call last):
File
"/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/code.py",
line 90, in runcode
exec(code, self.locals)
File "", line 1, in
File "/Users/cbarra/Projects/kompost/recipes/models.py", line 262, in
controller
deferred=True,
File "", line 2, in column_property
File "", line 2, in __init__
File
"/Users/cbarra/Projects/.venv/lib/python3.7/site-packages/sqlalchemy/util/deprecations.py"
, line 130, in warned
return fn(*args, **kwargs)
File
"/Users/cbarra/Projects/.venv/lib/python3.7/site-packages/sqlalchemy/orm/properties.py"
, line 134, in __init__
self._orig_columns = [expression._labeled(c) for c in columns]
File
"/Users/cbarra/Projects/.venv/lib/python3.7/site-packages/sqlalchemy/orm/properties.py"
, line 134, in
self._orig_columns = [expression._labeled(c) for c in columns]
File "", line 1, in
File
"/Users/cbarra/Projects/.venv/lib/python3.7/site-packages/sqlalchemy/sql/elements.py"
, line 4373, in _labeled
return element.label(None)
AttributeError: 'NoneType' object has no attribute 'label'
while when I try to use `undefer` with
models.EcRecipe.query.options(orm.undefer('controller'))
the error is different
Traceback (most recent call last):
File
"/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/code.py",
line 90, in runcode
exec(code, self.locals)
File "", line 1, in
File
"/Users/cbarra/Projects/.venv/lib/python3.7/site-packages/sqlalchemy/orm/query.py"
, line 1523, in options
return self._options(False, *args)
File "", line 2, in _options
File
"/Users/cbarra/Projects/.venv/lib/python3.7/site-packages/sqlalchemy/orm/base.py"
, line 220, in generate
fn(self, *args[1:], **kw)
File
"/Users/cbarra/Projects/.venv/lib/python3.7/site-packages/sqlalchemy/orm/query.py"
, line 1542, in _options
opt.process_query(self)
File
"/Users/cbarra/Projects/.venv/lib/python3.7/site-packages/sqlalchemy/orm/strategy_options.py"
, line 168, in process_query
self._process(query, True)
File
"/Users/cbarra/Projects/.venv/lib/python3.7/site-packages/sqlalchemy/orm/strategy_options.py"
, line 542, in _process
raiseerr,
File
"/Users/cbarra/Projects/.venv/lib/python3.7/site-packages/sqlalchemy/orm/strategy_options.py"
, line 720, in _bind_loader
raiseerr,
File
"/Users/cbarra/Projects/.venv/lib/python3.7/site-packages/sqlalchemy/orm/strategy_options.py"
, line 235, in _generate_path
attr = found_property = attr.property
AttributeError: 'property' object has no attribute 'property'
I am bit puzzled between property, hybrid_property and column_property,
what is the best way to have lazy attributes defined on a mixin?
--
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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