django---ORM之Q查询
filter 等方法中的关键字参数查询都是一起进行“AND” 的。 如果你需要执行更复杂的查询（例如OR 语句），你可以使用Q对象
调用Q
from django.db.models import Q
Q 对象可以使用c&(AND)和|(OR)操作符组合起来。
当一个操作符在两个Q 对象上使用时，它产生一个新的Q 对象。
Q(question__startswith='Who') | Q(question__startswith='What')
等同于SQL语句
WHERE question LIKE 'Who%' OR question LIKE 'What%'
如果一个查询函数有多个Q 对象参数（逗号隔开的），这些参数的逻辑关系为“AND"。示例：
Poll.objects.get(
Q(question__startswith='Who'),
Q(pub_date=date(2005, 5, 2)) | Q(pub_date=date(2005, 5, 6))
)
#等同于下列SQL语句：
SELECT * from polls WHERE question LIKE 'Who%'
AND (pub_date = '2005-05-02' OR pub_date = '2005-05-06')
Q 对象可以使用~ 操作符取反，这允许组合正常的查询和取反(NOT) 查询：
Q(question__startswith='Who') | ~Q(pub_date__year=2005)
查询函数可以混合使用Q对象和关键字参数。所有提供给查询函数的参数（关键字参数或Q 对象）都将"AND”在一起。但是，如果出现Q 对象，它必须位于所有关键字参数的前面。例如
Poll.objects.get(
Q(pub_date=date(2005, 5, 2)) | Q(pub_date=date(2005, 5, 6)),
question__startswith='Who')
#下列是不合法的查询条件
Poll.objects.get(
question__startswith='Who',
Q(pub_date=date(2005, 5, 2)) | Q(pub_date=date(2005, 5, 6)))
Q对象实例化使用：
# 获取搜索条件
condition_dict = json.loads(request.GET.get('condition'))
'''
{'sn__contains': ['1', '2', '3', '1'], 'hostname__contains': ['c1', 'c2', 'c3']}
'''
from django.db.models import Q
#产生第一个Q对象
con = Q()
for k,v in condition_dict.items():
#产生第二个Q对象
temp = Q()
temp.connector = 'OR' # Connection types AND = 'AND' OR = 'OR' default = AND
for item in v:
temp.children.append((k,item)) #children是Q父类Node的属性，默认是个列表
con.add(temp,'AND') # add 是父类Node的方法，
print(con)
'''
(AND: (OR: ('sn__contains', '1'), ('sn__contains', '1')), ('hostname__contains', 'c3'))
'''
models.Server.objects.filter(con)
#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Created by Mona on 2017/10/24
import copy
from django.utils.encoding import force_str, force_text
class Node(object):
"""
A single internal node in the tree graph. A Node should be viewed as a
connection (the root) with the children being either leaf nodes or other
Node instances.
"""
# Standard connector type. Clients usually won't use this at all and
# subclasses will usually override the value.
default = 'DEFAULT'
def __init__(self, children=None, connector=None, negated=False):
"""
Constructs a new Node. If no connector is given, the default will be
used.
"""
self.children = children[:] if children else []
self.connector = connector or self.default
self.negated = negated
# We need this because of django.db.models.query_utils.Q. Q. __init__() is
# problematic, but it is a natural Node subclass in all other respects.
@classmethod
def _new_instance(cls, children=None, connector=None, negated=False):
"""
This is called to create a new instance of this class when we need new
Nodes (or subclasses) in the internal code in this class. Normally, it
just shadows __init__(). However, subclasses with an __init__ signature
that is not an extension of Node.__init__ might need to implement this
method to allow a Node to create a new instance of them (if they have
any extra setting up to do).
"""
obj = Node(children, connector, negated)
obj.__class__ = cls
return obj
def __str__(self):
template = '(NOT (%s: %s))' if self.negated else '(%s: %s)'
return force_str(template % (self.connector, ', '.join(force_text(c) for c in self.children)))
def __repr__(self):
return str("<%s: %s>") % (self.__class__.__name__, self)
def __deepcopy__(self, memodict):
"""
Utility method used by copy.deepcopy().
"""
obj = Node(connector=self.connector, negated=self.negated)
obj.__class__ = self.__class__
obj.children = copy.deepcopy(self.children, memodict)
return obj
def __len__(self):
"""
The size of a node if the number of children it has.
"""
return len(self.children)
def __bool__(self):
"""
For truth value testing.
"""
return bool(self.children)
def __nonzero__(self): # Python 2 compatibility
return type(self).__bool__(self)
def __contains__(self, other):
"""
Returns True is 'other' is a direct child of this instance.
"""
return other in self.children
def add(self, data, conn_type, squash=True):
"""
Combines this tree and the data represented by data using the
connector conn_type. The combine is done by squashing the node other
away if possible.
This tree (self) will never be pushed to a child node of the
combined tree, nor will the connector or negated properties change.
The function returns a node which can be used in place of data
regardless if the node other got squashed or not.
If `squash` is False the data is prepared and added as a child to
this tree without further logic.
"""
if data in self.children:
return data
if not squash:
self.children.append(data)
return data
if self.connector == conn_type:
# We can reuse self.children to append or squash the node other.
if (isinstance(data, Node) and not data.negated and
(data.connector == conn_type or len(data) == 1)):
# We can squash the other node's children directly into this
# node. We are just doing (AB)(CD) == (ABCD) here, with the
# addition that if the length of the other node is 1 the
# connector doesn't matter. However, for the len(self) == 1
# case we don't want to do the squashing, as it would alter
# self.connector.
self.children.extend(data.children)
return self
else:
# We could use perhaps additional logic here to see if some
# children could be used for pushdown here.
self.children.append(data)
return data
else:
obj = self._new_instance(self.children, self.connector,
self.negated)
self.connector = conn_type
self.children = [obj, data]
return data
def negate(self):
"""
Negate the sense of the root connector.
"""
self.negated = not self.negated
class Q(Node):
"""
Encapsulates filters as objects that can then be combined logically (using
`&` and `|`).
"""
# Connection types
AND = 'AND'
OR = 'OR'
default = AND
def __init__(self, *args, **kwargs):
super(Q, self).__init__(children=list(args) + list(kwargs.items()))
def _combine(self, other, conn):
if not isinstance(other, Q):
raise TypeError(other)
obj = type(self)()
obj.connector = conn
obj.add(self, conn)
obj.add(other, conn)
return obj
def __or__(self, other):
return self._combine(other, self.OR)
def __and__(self, other):
return self._combine(other, self.AND)
def __invert__(self):
obj = type(self)()
obj.add(self, self.AND)
obj.negate()
return obj
def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False):
# We must promote any new joins to left outer joins so that when Q is
# used as an expression, rows aren't filtered due to joins.
clause, joins = query._add_q(self, reuse, allow_joins=allow_joins, split_subq=False)
query.promote_joins(joins)
return clause
#!/usr/bin/env python
# -*- coding: utf-8 -*-
# Created by Mona on 2017/10/24
import copy
from django.utils.encoding import force_str, force_text
class Node(object):
"""
A single internal node in the tree graph. A Node should be viewed as a
connection (the root) with the children being either leaf nodes or other
Node instances.
"""
# Standard connector type. Clients usually won't use this at all and
# subclasses will usually override the value.
default = 'DEFAULT'
def __init__(self, children=None, connector=None, negated=False):
"""
Constructs a new Node. If no connector is given, the default will be
used.
"""
self.children = children[:] if children else []
self.connector = connector or self.default
self.negated = negated
# We need this because of django.db.models.query_utils.Q. Q. __init__() is
# problematic, but it is a natural Node subclass in all other respects.
@classmethod
def _new_instance(cls, children=None, connector=None, negated=False):
"""
This is called to create a new instance of this class when we need new
Nodes (or subclasses) in the internal code in this class. Normally, it
just shadows __init__(). However, subclasses with an __init__ signature
that is not an extension of Node.__init__ might need to implement this
method to allow a Node to create a new instance of them (if they have
any extra setting up to do).
"""
obj = Node(children, connector, negated)
obj.__class__ = cls
return obj
def __str__(self):
template = '(NOT (%s: %s))' if self.negated else '(%s: %s)'
return force_str(template % (self.connector, ', '.join(force_text(c) for c in self.children)))
def __repr__(self):
return str("<%s: %s>") % (self.__class__.__name__, self)
def __deepcopy__(self, memodict):
"""
Utility method used by copy.deepcopy().
"""
obj = Node(connector=self.connector, negated=self.negated)
obj.__class__ = self.__class__
obj.children = copy.deepcopy(self.children, memodict)
return obj
def __len__(self):
"""
The size of a node if the number of children it has.
"""
return len(self.children)
def __bool__(self):
"""
For truth value testing.
"""
return bool(self.children)
def __nonzero__(self): # Python 2 compatibility
return type(self).__bool__(self)
def __contains__(self, other):
"""
Returns True is 'other' is a direct child of this instance.
"""
return other in self.children
def add(self, data, conn_type, squash=True):
"""
Combines this tree and the data represented by data using the
connector conn_type. The combine is done by squashing the node other
away if possible.
This tree (self) will never be pushed to a child node of the
combined tree, nor will the connector or negated properties change.
The function returns a node which can be used in place of data
regardless if the node other got squashed or not.
If `squash` is False the data is prepared and added as a child to
this tree without further logic.
"""
if data in self.children:
return data
if not squash:
self.children.append(data)
return data
if self.connector == conn_type:
# We can reuse self.children to append or squash the node other.
if (isinstance(data, Node) and not data.negated and
(data.connector == conn_type or len(data) == 1)):
# We can squash the other node's children directly into this
# node. We are just doing (AB)(CD) == (ABCD) here, with the
# addition that if the length of the other node is 1 the
# connector doesn't matter. However, for the len(self) == 1
# case we don't want to do the squashing, as it would alter
# self.connector.
self.children.extend(data.children)
return self
else:
# We could use perhaps additional logic here to see if some
# children could be used for pushdown here.
self.children.append(data)
return data
else:
obj = self._new_instance(self.children, self.connector,
self.negated)
self.connector = conn_type
self.children = [obj, data]
return data
def negate(self):
"""
Negate the sense of the root connector.
"""
self.negated = not self.negated
class Q(Node):
"""
Encapsulates filters as objects that can then be combined logically (using
`&` and `|`).
"""
# Connection types
AND = 'AND'
OR = 'OR'
default = AND
def __init__(self, *args, **kwargs):
super(Q, self).__init__(children=list(args) + list(kwargs.items()))
def _combine(self, other, conn):
if not isinstance(other, Q):
raise TypeError(other)
obj = type(self)()
obj.connector = conn
obj.add(self, conn)
obj.add(other, conn)
return obj
def __or__(self, other):
return self._combine(other, self.OR)
def __and__(self, other):
return self._combine(other, self.AND)
def __invert__(self):
obj = type(self)()
obj.add(self, self.AND)
obj.negate()
return obj
def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False):
# We must promote any new joins to left outer joins so that when Q is
# used as an expression, rows aren't filtered due to joins.
clause, joins = query._add_q(self, reuse, allow_joins=allow_joins, split_subq=False)
query.promote_joins(joins)
return clause
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