如何将django中Count()的输出转换为django 1.8中的FloatField
我正在使用django 1.8 我有两种型号:如何将django中Count()的输出转换为django 1.8中的FloatField,django,django-models,django-orm,Django,Django Models,Django Orm,我正在使用django 1.8 我有两种型号: class Query(models.Model): user = models.ForeignKey(settings.AUTH_USER_MODEL) title = models.TextField() details = models.TextField() pub_date = models.DateTimeField('date published') post_score=models.Floa
class Query(models.Model):
user = models.ForeignKey(settings.AUTH_USER_MODEL)
title = models.TextField()
details = models.TextField()
pub_date = models.DateTimeField('date published')
post_score=models.FloatField(default=0.0)
....
class Tags(models.Model):
"""docstring for Tags"""
tagname=models.TextField()
grouppostlist=models.ManyToManyField(Query,through='GroupPostsTag',through_fields=('tag','query'))
# and another model(it stores tags for a query)
class GroupPostsTag(models.Model):
query=models.ForeignKey('Query')
tag=models.models.ForeignKey('Tags')
现在我想根据“标记数”和查询的“post_分数”之和对查询进行排序。
我在找这样的东西:-
tagged_user_posts = Query.objects.filter(Q(tags__id__in=tags_list)).annotate(num_tags=Cast(Count('tags'),models.FloatField())).annotate(post_scores=F('num_tags')+F('post_score')).order_by('-post_scores')
在django 1.10中提供。那么我可以使用什么替代方案呢 正如我在评论中所说,您可以简单地复制
Cast
类的源代码,并将其保存在项目中并使用它
结果不是那么简单。您还需要更改强制转换.as\u sql。而且,无需对Func.as\u sql
进行super
调用
只需复制以下代码并将其保存在项目中。我已经测试过了,效果很好
from django.db.models import Func, fields
class Cast(Func):
"""
Coerce an expression to a new field type.
"""
function = 'CAST'
template = '%(function)s(%(expressions)s AS %(db_type)s)'
mysql_types = {
fields.CharField: 'char',
fields.IntegerField: 'signed integer',
fields.FloatField: 'signed',
}
def __init__(self, expression, output_field):
super(Cast, self).__init__(expression, output_field=output_field)
def as_sql(self, compiler, connection, function=None, template=None, arg_joiner=None, **extra_context):
if 'db_type' not in extra_context:
extra_context['db_type'] = self._output_field.db_type(connection)
connection.ops.check_expression_support(self)
sql_parts = []
params = []
for arg in self.source_expressions:
arg_sql, arg_params = compiler.compile(arg)
sql_parts.append(arg_sql)
params.extend(arg_params)
data = self.extra.copy()
data.update(**extra_context)
# Use the first supplied value in this order: the parameter to this
# method, a value supplied in __init__()'s **extra (the value in
# `data`), or the value defined on the class.
if function is not None:
data['function'] = function
else:
data.setdefault('function', self.function)
template = template or data.get('template', self.template)
arg_joiner = arg_joiner or data.get('arg_joiner', self.arg_joiner)
data['expressions'] = data['field'] = arg_joiner.join(sql_parts)
return template % data, params
def as_mysql(self, compiler, connection):
extra_context = {}
output_field_class = type(self._output_field)
if output_field_class in self.mysql_types:
extra_context['db_type'] = self.mysql_types[output_field_class]
return self.as_sql(compiler, connection, **extra_context)
def as_postgresql(self, compiler, connection):
# CAST would be valid too, but the :: shortcut syntax is more readable.
return self.as_sql(compiler, connection, template='%(expressions)s::%(db_type)s')
正如您在django 1.10的问题中提到的,您可以使用内置的Cast函数。对于旧版本,您可以使用
您可以将
Cast
定义为
def Cast(what, as_type):
if isinstance(as_type, Field):
as_type = as_type.db_type(connection)
return Func(
what,
template='%(function)s(%(expressions)s AS %(type)s)',
function='Cast',
type=as_type,
)
它是开源的。您只需复制并将其保存在项目中的文件中即可。我尝试过这样做,但它给了我一个错误:
TypeError:as\u sql()得到了一个意外的关键字参数“db\u type”
我对源代码进行了一些修改,并在答案中添加了它。希望有帮助。它显示了一个错误FieldError:表达式包含混合类型。您必须设置output_field
使用ExpressionWrapper包装F对象的总和应该可以解决此问题。现在试试看。
def Cast(what, as_type):
if isinstance(as_type, Field):
as_type = as_type.db_type(connection)
return Func(
what,
template='%(function)s(%(expressions)s AS %(type)s)',
function='Cast',
type=as_type,
)