managers.py

#!/usr/bin/env python
# vim: ai ts=4 sts=4 et sw=4 coding=utf-8
#
#    This software is derived from EAV-Django originally written and
#    copyrighted by Andrey Mikhaylenko <http://pypi.python.org/pypi/eav-django>
#
#    This is free software: you can redistribute it and/or modify
#    it under the terms of the GNU Lesser General Public License as published
#    by the Free Software Foundation, either version 3 of the License, or
#    (at your option) any later version.
#
#    This software is distributed in the hope that it will be useful,
#    but WITHOUT ANY WARRANTY; without even the implied warranty of
#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#    GNU Lesser General Public License for more details.
#
#    You should have received a copy of the GNU Lesser General Public License
#    along with EAV-Django.  If not, see <http://gnu.org/licenses/>.
'''
********
managers
********
Contains the custom manager used by entities registered with eav.

Functions and Classes
---------------------
'''
from functools import wraps

from django.db import models

from .models import Attribute, Value


def eav_filter(func):
    '''
    Decorator used to wrap filter and exlclude methods.  Passes args through
    expand_q_filters and kwargs through expand_eav_filter. Returns the
    called function (filter or exclude)
    '''

    @wraps(func)
    def wrapper(self, *args, **kwargs):
        new_args = []
        for arg in args:
            if isinstance(arg, models.Q):
                # modify Q objects (warning: recursion ahead)
                arg = expand_q_filters(arg, self.model)
            new_args.append(arg)

        new_kwargs = {}
        for key, value in kwargs.items():
            # modify kwargs (warning: recursion ahead)
            new_key, new_value = expand_eav_filter(self.model, key, value)
            new_kwargs.update({new_key: new_value})

        return func(self, *new_args, **new_kwargs)
    return wrapper


def expand_q_filters(q, root_cls):
    '''
    Takes a Q object and a model class.
    Recursivley passes each filter / value in the Q object tree leaf nodes
    through expand_eav_filter
    '''
    new_children = []
    for qi in q.children:
        if type(qi) is tuple:
            # this child is a leaf node: in Q this is a 2-tuple of:
            # (filter parameter, value)
            key, value = expand_eav_filter(root_cls, *qi)
            new_children.append(models.Q(**{key: value}))
        else:
            # this child is another Q node: recursify!
            new_children.append(expand_q_filters(qi, root_cls))
    q.children = new_children
    return q


def expand_eav_filter(model_cls, key, value):
    '''
    Accepts a model class and a key, value.
    Recurisively replaces any eav filter with a subquery.

    For example::

        key = 'eav__height'
        value = 5

    Would return::

        key = 'eav_values__in'
        value = Values.objects.filter(value_int=5, attribute__slug='height')
    '''
    fields = key.split('__')

    config_cls = getattr(model_cls, '_eav_config_cls', None)
    if len(fields) > 1 and config_cls and \
       fields[0] == config_cls.eav_attr:
        slug = fields[1]
        gr_name = config_cls.generic_relation_attr
        datatype = Attribute.objects.get(slug=slug).datatype

        lookup = '__%s' % fields[2] if len(fields) > 2 else ''
        kwargs = {'value_%s%s' % (datatype, lookup): value,
                  'attribute__slug': slug}
        value = Value.objects.filter(**kwargs)

        return '%s__in' % gr_name, value

    try:
        field, m, direct, m2m = model_cls._meta.get_field_by_name(fields[0])
    except models.FieldDoesNotExist:
        return key, value

    if direct:
        return key, value
    else:
        sub_key = '__'.join(fields[1:])
        key, value = expand_eav_filter(field.model, sub_key, value)
        return '%s__%s' % (fields[0], key), value


class EntityManager(models.Manager):
    '''
    Our custom manager, overriding ``models.Manager``
    '''

    @eav_filter
    def filter(self, *args, **kwargs):
        '''
        Pass *args* and *kwargs* through :func:`eav_filter`, then pass to
        the ``models.Manager`` filter method.
        '''
        return super(EntityManager, self).filter(*args, **kwargs).distinct()

    @eav_filter
    def exclude(self, *args, **kwargs):
        '''
        Pass *args* and *kwargs* through :func:`eav_filter`, then pass to
        the ``models.Manager`` exclude method.
        '''
        return super(EntityManager, self).exclude(*args, **kwargs).distinct()

    @eav_filter
    def get(self, *args, **kwargs):
        '''
        Pass *args* and *kwargs* through :func:`eav_filter`, then pass to
        the ``models.Manager`` get method.
        '''
        return super(EntityManager, self).get(*args, **kwargs)

    def create(self, **kwargs):
        '''
        Parse eav attributes out of *kwargs*, then try to create and save
        the object, then assign and save it's eav attributes.
        '''
        config_cls = getattr(self.model, '_eav_config_cls', None)

        if not config_cls or config_cls.manager_only:
            return super(EntityManager, self).create(**kwargs)

        #attributes = config_cls.get_attributes()
        prefix = '%s__' % config_cls.eav_attr
        attributes_name = [x.name for x in config_cls.get_attributes()]

        new_kwargs = {}
        eav_kwargs = {}
        for key, value in kwargs.iteritems():
            if key.startswith(prefix):
                if key[len(prefix):] in attributes_name:
                    eav_kwargs.update({key[len(prefix):]: value})
                else:
                    raise AttributeError("Attribute %s not in model attributes"%(key[len(prefix):],))
            else:
                new_kwargs.update({key: value})

        obj = self.model(**new_kwargs)
        obj_eav = getattr(obj, config_cls.eav_attr)
        for key, value in eav_kwargs.iteritems():
            setattr(obj_eav, key, value)
        obj.save()
        return obj

    def get_or_create(self, **kwargs):
        '''
        Reproduces the behavior of get_or_create, eav friendly.
        '''
        try:
            return self.get(**kwargs), False
        except self.model.DoesNotExist:
            return self.create(**kwargs), True