351 lines
11 KiB
Python
351 lines
11 KiB
Python
# ext/index.py
|
|
# Copyright (C) 2005-2019 the SQLAlchemy authors and contributors
|
|
# <see AUTHORS file>
|
|
#
|
|
# This module is part of SQLAlchemy and is released under
|
|
# the MIT License: http://www.opensource.org/licenses/mit-license.php
|
|
|
|
"""Define attributes on ORM-mapped classes that have "index" attributes for
|
|
columns with :class:`~.types.Indexable` types.
|
|
|
|
"index" means the attribute is associated with an element of an
|
|
:class:`~.types.Indexable` column with the predefined index to access it.
|
|
The :class:`~.types.Indexable` types include types such as
|
|
:class:`~.types.ARRAY`, :class:`~.types.JSON` and
|
|
:class:`~.postgresql.HSTORE`.
|
|
|
|
|
|
|
|
The :mod:`~sqlalchemy.ext.indexable` extension provides
|
|
:class:`~.schema.Column`-like interface for any element of an
|
|
:class:`~.types.Indexable` typed column. In simple cases, it can be
|
|
treated as a :class:`~.schema.Column` - mapped attribute.
|
|
|
|
|
|
.. versionadded:: 1.1
|
|
|
|
Synopsis
|
|
========
|
|
|
|
Given ``Person`` as a model with a primary key and JSON data field.
|
|
While this field may have any number of elements encoded within it,
|
|
we would like to refer to the element called ``name`` individually
|
|
as a dedicated attribute which behaves like a standalone column::
|
|
|
|
from sqlalchemy import Column, JSON, Integer
|
|
from sqlalchemy.ext.declarative import declarative_base
|
|
from sqlalchemy.ext.indexable import index_property
|
|
|
|
Base = declarative_base()
|
|
|
|
class Person(Base):
|
|
__tablename__ = 'person'
|
|
|
|
id = Column(Integer, primary_key=True)
|
|
data = Column(JSON)
|
|
|
|
name = index_property('data', 'name')
|
|
|
|
|
|
Above, the ``name`` attribute now behaves like a mapped column. We
|
|
can compose a new ``Person`` and set the value of ``name``::
|
|
|
|
>>> person = Person(name='Alchemist')
|
|
|
|
The value is now accessible::
|
|
|
|
>>> person.name
|
|
'Alchemist'
|
|
|
|
Behind the scenes, the JSON field was initialized to a new blank dictionary
|
|
and the field was set::
|
|
|
|
>>> person.data
|
|
{"name": "Alchemist'}
|
|
|
|
The field is mutable in place::
|
|
|
|
>>> person.name = 'Renamed'
|
|
>>> person.name
|
|
'Renamed'
|
|
>>> person.data
|
|
{'name': 'Renamed'}
|
|
|
|
When using :class:`.index_property`, the change that we make to the indexable
|
|
structure is also automatically tracked as history; we no longer need
|
|
to use :class:`~.mutable.MutableDict` in order to track this change
|
|
for the unit of work.
|
|
|
|
Deletions work normally as well::
|
|
|
|
>>> del person.name
|
|
>>> person.data
|
|
{}
|
|
|
|
Above, deletion of ``person.name`` deletes the value from the dictionary,
|
|
but not the dictionary itself.
|
|
|
|
A missing key will produce ``AttributeError``::
|
|
|
|
>>> person = Person()
|
|
>>> person.name
|
|
...
|
|
AttributeError: 'name'
|
|
|
|
Unless you set a default value::
|
|
|
|
>>> class Person(Base):
|
|
>>> __tablename__ = 'person'
|
|
>>>
|
|
>>> id = Column(Integer, primary_key=True)
|
|
>>> data = Column(JSON)
|
|
>>>
|
|
>>> name = index_property('data', 'name', default=None) # See default
|
|
|
|
>>> person = Person()
|
|
>>> print(person.name)
|
|
None
|
|
|
|
|
|
The attributes are also accessible at the class level.
|
|
Below, we illustrate ``Person.name`` used to generate
|
|
an indexed SQL criteria::
|
|
|
|
>>> from sqlalchemy.orm import Session
|
|
>>> session = Session()
|
|
>>> query = session.query(Person).filter(Person.name == 'Alchemist')
|
|
|
|
The above query is equivalent to::
|
|
|
|
>>> query = session.query(Person).filter(Person.data['name'] == 'Alchemist')
|
|
|
|
Multiple :class:`.index_property` objects can be chained to produce
|
|
multiple levels of indexing::
|
|
|
|
from sqlalchemy import Column, JSON, Integer
|
|
from sqlalchemy.ext.declarative import declarative_base
|
|
from sqlalchemy.ext.indexable import index_property
|
|
|
|
Base = declarative_base()
|
|
|
|
class Person(Base):
|
|
__tablename__ = 'person'
|
|
|
|
id = Column(Integer, primary_key=True)
|
|
data = Column(JSON)
|
|
|
|
birthday = index_property('data', 'birthday')
|
|
year = index_property('birthday', 'year')
|
|
month = index_property('birthday', 'month')
|
|
day = index_property('birthday', 'day')
|
|
|
|
Above, a query such as::
|
|
|
|
q = session.query(Person).filter(Person.year == '1980')
|
|
|
|
On a PostgreSQL backend, the above query will render as::
|
|
|
|
SELECT person.id, person.data
|
|
FROM person
|
|
WHERE person.data -> %(data_1)s -> %(param_1)s = %(param_2)s
|
|
|
|
Default Values
|
|
==============
|
|
|
|
:class:`.index_property` includes special behaviors for when the indexed
|
|
data structure does not exist, and a set operation is called:
|
|
|
|
* For an :class:`.index_property` that is given an integer index value,
|
|
the default data structure will be a Python list of ``None`` values,
|
|
at least as long as the index value; the value is then set at its
|
|
place in the list. This means for an index value of zero, the list
|
|
will be initialized to ``[None]`` before setting the given value,
|
|
and for an index value of five, the list will be initialized to
|
|
``[None, None, None, None, None]`` before setting the fifth element
|
|
to the given value. Note that an existing list is **not** extended
|
|
in place to receive a value.
|
|
|
|
* for an :class:`.index_property` that is given any other kind of index
|
|
value (e.g. strings usually), a Python dictionary is used as the
|
|
default data structure.
|
|
|
|
* The default data structure can be set to any Python callable using the
|
|
:paramref:`.index_property.datatype` parameter, overriding the previous
|
|
rules.
|
|
|
|
|
|
Subclassing
|
|
===========
|
|
|
|
:class:`.index_property` can be subclassed, in particular for the common
|
|
use case of providing coercion of values or SQL expressions as they are
|
|
accessed. Below is a common recipe for use with a PostgreSQL JSON type,
|
|
where we want to also include automatic casting plus ``astext()``::
|
|
|
|
class pg_json_property(index_property):
|
|
def __init__(self, attr_name, index, cast_type):
|
|
super(pg_json_property, self).__init__(attr_name, index)
|
|
self.cast_type = cast_type
|
|
|
|
def expr(self, model):
|
|
expr = super(pg_json_property, self).expr(model)
|
|
return expr.astext.cast(self.cast_type)
|
|
|
|
The above subclass can be used with the PostgreSQL-specific
|
|
version of :class:`.postgresql.JSON`::
|
|
|
|
from sqlalchemy import Column, Integer
|
|
from sqlalchemy.ext.declarative import declarative_base
|
|
from sqlalchemy.dialects.postgresql import JSON
|
|
|
|
Base = declarative_base()
|
|
|
|
class Person(Base):
|
|
__tablename__ = 'person'
|
|
|
|
id = Column(Integer, primary_key=True)
|
|
data = Column(JSON)
|
|
|
|
age = pg_json_property('data', 'age', Integer)
|
|
|
|
The ``age`` attribute at the instance level works as before; however
|
|
when rendering SQL, PostgreSQL's ``->>`` operator will be used
|
|
for indexed access, instead of the usual index operator of ``->``::
|
|
|
|
>>> query = session.query(Person).filter(Person.age < 20)
|
|
|
|
The above query will render::
|
|
|
|
SELECT person.id, person.data
|
|
FROM person
|
|
WHERE CAST(person.data ->> %(data_1)s AS INTEGER) < %(param_1)s
|
|
|
|
""" # noqa
|
|
from __future__ import absolute_import
|
|
|
|
from sqlalchemy import inspect
|
|
from ..ext.hybrid import hybrid_property
|
|
from ..orm.attributes import flag_modified
|
|
|
|
|
|
__all__ = ["index_property"]
|
|
|
|
|
|
class index_property(hybrid_property): # noqa
|
|
"""A property generator. The generated property describes an object
|
|
attribute that corresponds to an :class:`~.types.Indexable`
|
|
column.
|
|
|
|
.. versionadded:: 1.1
|
|
|
|
.. seealso::
|
|
|
|
:mod:`sqlalchemy.ext.indexable`
|
|
|
|
"""
|
|
|
|
_NO_DEFAULT_ARGUMENT = object()
|
|
|
|
def __init__(
|
|
self,
|
|
attr_name,
|
|
index,
|
|
default=_NO_DEFAULT_ARGUMENT,
|
|
datatype=None,
|
|
mutable=True,
|
|
onebased=True,
|
|
):
|
|
"""Create a new :class:`.index_property`.
|
|
|
|
:param attr_name:
|
|
An attribute name of an `Indexable` typed column, or other
|
|
attribute that returns an indexable structure.
|
|
:param index:
|
|
The index to be used for getting and setting this value. This
|
|
should be the Python-side index value for integers.
|
|
:param default:
|
|
A value which will be returned instead of `AttributeError`
|
|
when there is not a value at given index.
|
|
:param datatype: default datatype to use when the field is empty.
|
|
By default, this is derived from the type of index used; a
|
|
Python list for an integer index, or a Python dictionary for
|
|
any other style of index. For a list, the list will be
|
|
initialized to a list of None values that is at least
|
|
``index`` elements long.
|
|
:param mutable: if False, writes and deletes to the attribute will
|
|
be disallowed.
|
|
:param onebased: assume the SQL representation of this value is
|
|
one-based; that is, the first index in SQL is 1, not zero.
|
|
"""
|
|
|
|
if mutable:
|
|
super(index_property, self).__init__(
|
|
self.fget, self.fset, self.fdel, self.expr
|
|
)
|
|
else:
|
|
super(index_property, self).__init__(
|
|
self.fget, None, None, self.expr
|
|
)
|
|
self.attr_name = attr_name
|
|
self.index = index
|
|
self.default = default
|
|
is_numeric = isinstance(index, int)
|
|
onebased = is_numeric and onebased
|
|
|
|
if datatype is not None:
|
|
self.datatype = datatype
|
|
else:
|
|
if is_numeric:
|
|
self.datatype = lambda: [None for x in range(index + 1)]
|
|
else:
|
|
self.datatype = dict
|
|
self.onebased = onebased
|
|
|
|
def _fget_default(self):
|
|
if self.default == self._NO_DEFAULT_ARGUMENT:
|
|
raise AttributeError(self.attr_name)
|
|
else:
|
|
return self.default
|
|
|
|
def fget(self, instance):
|
|
attr_name = self.attr_name
|
|
column_value = getattr(instance, attr_name)
|
|
if column_value is None:
|
|
return self._fget_default()
|
|
try:
|
|
value = column_value[self.index]
|
|
except (KeyError, IndexError):
|
|
return self._fget_default()
|
|
else:
|
|
return value
|
|
|
|
def fset(self, instance, value):
|
|
attr_name = self.attr_name
|
|
column_value = getattr(instance, attr_name, None)
|
|
if column_value is None:
|
|
column_value = self.datatype()
|
|
setattr(instance, attr_name, column_value)
|
|
column_value[self.index] = value
|
|
setattr(instance, attr_name, column_value)
|
|
if attr_name in inspect(instance).mapper.attrs:
|
|
flag_modified(instance, attr_name)
|
|
|
|
def fdel(self, instance):
|
|
attr_name = self.attr_name
|
|
column_value = getattr(instance, attr_name)
|
|
if column_value is None:
|
|
raise AttributeError(self.attr_name)
|
|
try:
|
|
del column_value[self.index]
|
|
except KeyError:
|
|
raise AttributeError(self.attr_name)
|
|
else:
|
|
setattr(instance, attr_name, column_value)
|
|
flag_modified(instance, attr_name)
|
|
|
|
def expr(self, model):
|
|
column = getattr(model, self.attr_name)
|
|
index = self.index
|
|
if self.onebased:
|
|
index += 1
|
|
return column[index]
|