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SQLConstruct-0.2.4
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مشاهده بیشترتوضیحات
Functional approach to query database using SQLAlchemy
| ویژگی | مقدار |
|---|---|
| سیستم عامل | OS Independent |
| نام فایل | SQLConstruct-0.2.4 |
| نام | SQLConstruct |
| نسخه کتابخانه | 0.2.4 |
| نگهدارنده | [] |
| ایمیل نگهدارنده | [] |
| نویسنده | Vladimir Magamedov |
| ایمیل نویسنده | vladimir@magamedov.com |
| آدرس صفحه اصلی | https://github.com/vmagamedov/sqlconstruct |
| آدرس اینترنتی | https://pypi.org/project/SQLConstruct/ |
| مجوز | BSD |
============
SQLConstruct
============
`SQLConstruct` is a functional approach to query database using `SQLAlchemy`
library. It was written to reach more speed without introducing unmaintainable
and verbose code. On the contrary, code becomes simpler, so there are less
chances of shooting yourself in the foot.
Main problems it aims to solve:
- ORM overhead in read-only ``SELECT`` queries;
- Network traffic when loading unnecessary columns;
- Code complexity;
- N+1 problem.
Final
=====
You describe what you want to get from the database:
.. code-block:: python
from sqlconstruct import Construct, if_
product_struct = Construct({
'name': Product.name,
'url': url_for_product.defn(Product),
'image_url': if_(
Image.id,
then_=url_for_image.defn(Image, 100, 100),
else_=None,
),
})
And you get it. `SQLConstruct` knows which columns you need and how transform
them into suitable to use format:
.. code-block:: python
>>> product = (
... session.query(product_struct)
... .outerjoin(Product.image)
... .first()
... )
...
>>> product.name
'Foo product'
>>> product.url
'/p1-foo-product.html'
>>> product.image_url
'//images.example.st/123-100x100-foo.jpg'
Full story
==========
Basic preparations:
.. code-block:: python
from sqlalchemy import create_engine
from sqlalchemy import Column, Integer, String, Text, ForeignKey
from sqlalchemy.orm import Session, relationship, eagerload
from sqlalchemy.ext.declarative import declarative_base
engine = create_engine('sqlite://')
Base = declarative_base()
class Image(Base):
__tablename__ = 'image'
id = Column(Integer, primary_key=True)
name = Column(String)
class Product(Base):
__tablename__ = 'product'
id = Column(Integer, primary_key=True)
name = Column(String)
image_id = Column(Integer, ForeignKey(Image.id))
description = Column(Text)
image = relationship(Image)
Base.metadata.create_all(engine)
session = Session(engine)
session.add(Product(name='Foo product', image=Image(name='Foo.jpg')))
session.commit()
def slugify(name):
# very dumb implementation, just for an example
return name.lower().replace(' ', '-')
def url_for_product(product):
return '/p{id}-{name}.html'.format(
id=product.id,
name=slugify(product.name),
)
def url_for_image(image, width, height):
return '//images.example.st/{id}-{width}x{height}-{name}'.format(
id=image.id,
width=width,
height=height,
name=slugify(image.name),
)
Usual way:
.. code-block:: python
>>> product = (
... session.query(Product)
... .options(eagerload(Product.image))
... .first()
... )
...
>>> product.name
u'Foo product'
>>> url_for_product(product)
'/p1-foo-product.html'
>>> url_for_image(product.image, 100, 100) if product.image else None
'//images.example.st/1-100x100-foo.jpg'
Disadvantages:
- ``description`` column isn't deferred, it will be loaded every time;
- if you will mark ``description`` column as deferred, this can introduce N+1
problem somewhere else in your project;
- if you forgot to ``eagerload`` ``Product.image`` you will also get N+1
problem;
- you have to pass model instances as arguments everywhere in the project and
this tends to code complexity, because you don't know how they will be used in
the future;
- model instances creation isn't cheap, CPU time grows with number of columns,
even if they are all deferred.
Initial solution:
.. code-block:: python
from sqlconstruct import Construct, apply_, if_
def url_for_product(product_id, product_name):
return '/p{id}-{name}.html'.format(
id=product_id,
name=slugify(product_name),
)
def url_for_image(image_id, image_name, width, height):
return '//images.example.st/{id}-{width}x{height}-{name}'.format(
id=image_id,
width=width,
height=height,
name=slugify(image_name),
)
product_struct = Construct({
'name': Product.name,
'url': apply_(url_for_product, args=[Product.id, Product.name]),
'image_url': if_(
Image.id,
then_=apply_(url_for_image, args=[Image.id, Image.name, 100, 100]),
else_=None,
),
})
Usage:
.. code-block:: python
>>> product = (
... session.query(product_struct)
... .outerjoin(Product.image)
... .first()
... )
...
>>> product.name
u'Foo product'
>>> product.url
'/p1-foo-product.html'
>>> product.image_url
'//images.example.st/1-100x100-foo.jpg'
Advantages:
- you're loading only what you need, no extra network traffic, no need to
defer/undefer columns;
- ``url_for_product`` and ``url_for_image`` functions can't add complexity,
because they are forced to define all needed columns as arguments;
- you're working with precomputed values (urls in this example).
Disadvantages:
- code of functions is hard to refactor and reuse, because you should specify or
pass all the arguments every time;
- you should be careful with joins, because if you wouldn't specify them
explicitly, `SQLAlchemy` will produce cartesian product of the tables
(``SELECT ... FROM product, image WHERE ...``), which will return wrong
results and hurt your performance.
To address first disadvantage, `SQLConstruct` provides ``define`` decorator,
which gives you ability to define hybrid functions to use them in different
ways:
.. code-block:: python
from sqlconstruct import define
@define
def url_for_product(product):
def body(product_id, product_name):
return '/p{id}-{name}.html'.format(
id=product_id,
name=slugify(product_name),
)
return body, [product.id, product.name]
@define
def url_for_image(image, width, height):
def body(image_id, image_name, width, height):
return '//images.example.st/{id}-{width}x{height}-{name}'.format(
id=image_id,
width=width,
height=height,
name=slugify(image_name),
)
return body, [image.id, image.name, width, height]
Now these functions can be used in these ways:
.. code-block:: python
>>> product = session.query(Product).first()
>>> url_for_product(product) # objective style
'/p1-foo-product.html'
>>> url_for_product.defn(Product) # apply_ declaration
<sqlconstruct.apply_ at 0x000000000>
>>> url_for_product.func(product.id, product.name) # functional style
'/p1-foo-product.html'
Modified final ``Construct`` definition:
.. code-block:: python
product_struct = Construct({
'name': Product.name,
'url': url_for_product.defn(Product),
'image_url': if_(
Image.id,
then_=url_for_image.defn(Image, 100, 100),
else_=None,
),
})
Installation
============
To install `SQLConstruct`, simply:
.. code-block:: shell
$ pip install sqlconstruct
Tested `Python` versions: 2.7, 3.4, 3.8.
Tested `SQLAlchemy` versions: 1.0, 1.1, 1.2, 1.3.
Examples above are using `SQLAlchemy` >= 0.9, if you are using older versions,
you will have to do next changes in your project configuration:
.. code-block:: python
from sqlconstruct import QueryMixin
from sqlalchemy.orm.query import Query as BaseQuery
class Query(QueryMixin, BaseQuery):
pass
session = Session(engine, query_cls=Query)
Flask-SQLAlchemy:
.. code-block:: python
from flask.ext.sqlalchemy import SQLAlchemy
db = SQLAlchemy(app, session_options={'query_cls': Query})
or
.. code-block:: python
db = SQLAlchemy(session_options={'query_cls': Query})
db.init_app(app)
License
=======
`SQLConstruct` is distributed under the BSD license. See LICENSE.txt for more
details.
نحوه نصب
نصب پکیج whl SQLConstruct-0.2.4:
pip install SQLConstruct-0.2.4.whl
نصب پکیج tar.gz SQLConstruct-0.2.4:
pip install SQLConstruct-0.2.4.tar.gz