具有距离值的GeoDjango距离滤波器存储在模型中 - 查询 [英] GeoDjango distance filter with distance value stored within model - query

问题描述

我有一个订单模型，它有一个来源 PointField和范围 IntegerField。此外，还有一个 UserProfile 模型，它有一个 geo_location PointField。现在，我有一个用户实例，用户。我想选择所有订单，其距离 Order.origin 和 user.userprofile之间的距离。地理位置小于 Order.range 模型字段中的值（米）。

I have an Order model, that has an origin PointField and a range IntegerField. Furthermore, there is an UserProfile model, which has a geo_location PointField. Now, I have an User instance, user. I want to select all Orders, whose distance between Order.origin and user.userprofile.geo_location is less then the value (meters) in the Order.range model field.

再次简化的模型：

class Order(models.Model):
    origin = models.PointField()
    range = models.IntegerField(blank=True, default=10000)

class UserProfile(models.Model):
    geo_location = models.PointField()

我有这个工作（静静地传递距离）：

I've got this working (passing the distance statically):

>>> Order.objects.filter(origin__distance_lte=(user.profile.geo_location, D(m=3000)))

我的下一个（不成功）尝试使用 F（ ）表达式使用 Order.range 字段中的值：

My next (unsuccessful) try was to use an F() expression to use the value from the Order.range field:

>>> Order.objects.filter(origin__distance_lte=(user.profile.geo_location, D(m=F('range'))))
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/Users/danger/devel/.virtualenvs/proj/lib/python2.7/site-packages/django/contrib/gis/measure.py", line 165, in __init__
self.m, self._default_unit = self.default_units(kwargs)
  File "/Users/danger/devel/.virtualenvs/proj/lib/python2.7/site-packages/django/contrib/gis/measure.py", line 49, in default_units
if not isinstance(value, float): value = float(value)
 TypeError: float() argument must be a string or a number

我认为问题是D（）不是懒惰地运行 - 我可以理解。
所以我试图从原来的$ code>范围字段（整数），我应该工作，但是：

I think the problem is that the D() isn't ran lazily - I can understand that. So I tried to just take the raw value from the range field (integer) which I supposed to work, but:

>>> Order.objects.filter(origin__distance_lte=(user.profile.geo_location, F('range')))
Traceback (most recent call last):
File "<console>", line 1, in <module>
File "/Users/danger/devel/.virtualenvs/proj/lib/python2.7/site-packages/django/db/models/query.py", line 69, in __repr__
data = list(self[:REPR_OUTPUT_SIZE + 1])
File "/Users/danger/devel/.virtualenvs/proj/lib/python2.7/site-packages/django/db/models/query.py", line 84, in __len__
self._result_cache.extend(self._iter)
File "/Users/danger/devel/.virtualenvs/proj/lib/python2.7/site-packages/django/db/models/query.py", line 273, in iterator
for row in compiler.results_iter():
File "/Users/danger/devel/.virtualenvs/proj/lib/python2.7/site-packages/django/db/models/sql/compiler.py", line 680, in results_iter
for rows in self.execute_sql(MULTI):
File "/Users/danger/devel/.virtualenvs/proj/lib/python2.7/site-packages/django/db/models/sql/compiler.py", line 725, in execute_sql
sql, params = self.as_sql()
File "/Users/danger/devel/.virtualenvs/proj/lib/python2.7/site-packages/django/db/models/sql/compiler.py", line 68, in as_sql
where, w_params = self.query.where.as_sql(qn=qn, connection=self.connection)
File "/Users/danger/devel/.virtualenvs/proj/lib/python2.7/site-packages/django/db/models/sql/where.py", line 92, in as_sql
sql, params = child.as_sql(qn=qn, connection=connection)
File "/Users/danger/devel/.virtualenvs/proj/lib/python2.7/site-packages/django/db/models/sql/where.py", line 95, in as_sql
sql, params = self.make_atom(child, qn, connection)
File "/Users/danger/devel/.virtualenvs/proj/lib/python2.7/site-packages/django/contrib/gis/db/models/sql/where.py", line 47, in make_atom
spatial_sql = connection.ops.spatial_lookup_sql(data, lookup_type, params_or_value, lvalue.field, qn)
File "/Users/danger/devel/.virtualenvs/proj/lib/python2.7/site-packages/django/contrib/gis/db/backends/postgis/operations.py", line 531, in spatial_lookup_sql
raise ValueError('Argument type should be %s, got %s instead.' % (arg_type, type(value[1])))
ValueError: Argument type should be (<class 'decimal.Decimal'>, <class 'django.contrib.gis.measure.Distance'>, <type 'float'>, <type 'int'>, <type 'long'>), got <class 'django.db.models.expressions.F'> instead.

那么我该怎么做呢？任何帮助是赞赏！

So how can I accomplish what I am trying to? Any help is appreciated!

推荐答案

我想你将不得不删除一些SQL来做你想要的，因为GeoDjango帮助者有一种方法可以制作一个合适的距离对象，它同时是Django F 对象（即字段查找）。你不会说你使用哪个数据库，但是在PostGIS中你可以这样做：

I think you're going to have to drop some SQL in to do what you want, as the GeoDjango helpers don't have a way of you making a suitable Distance object that is simultaneously a Django F object (ie field lookup). You don't say which database you're using, but here's how you do it with PostGIS:

Order.objects.all().extra(
    where=['ST_Distance(origin, ST_PointFromText(%s, 4326)) <= CAST(range AS double precision) / 1000'],
    params=[user.profile.geo_location.wkt]
)

我们来解释这里发生了什么，因为它很棘手。从左边：

Let's explain what's happening here, because it's pretty thorny. Going from the left:

• .extra（）允许您添加额外的字段和限制进查询;这里我们添加一个限制


• ST_Distance（） 是PostGIS函数，GeoDjango distance_lte operator convert into（from Django文档）


• ST_PointFromText（） 将WKT语法转换为PostGIS几何对象


• 4326 是 Django的默认SRID ，但不适用于PostGIS，所以我们必须指定它


• 我们必须 CAST 你的领域要加倍精度，因为你使用一个整数


• 那么我们必须除以1000，从米转换成公里，我 它给出了他们的WKT表示，我们之前在 ST_PointFromText（）调用

• .extra() allows you to add extra fields and restrictions into a query; here we're adding a restriction
• ST_Distance() is the PostGIS function that the GeoDjango distance_lte operator converts into (from the Django documentation)
• ST_PointFromText() converts from WKT syntax into a PostGIS Geometry object
• 4326 is the default SRID for Django, but not for PostGIS so we have to specify it
• we have to CAST your field to double precision because you're using an integer
• then we have to divide by 1000 to convert from metres into kilometres, which I believe is what we need
• GeoDjango Point fields have an accessor .wkt which gives their WKT representation, which we needed earlier in our ST_PointFromText() call

请注意，根据PostGIS文档， ST_Distance（）不使用索引，因此您可能需要使用 ST_DWithin（）（在 ST_Distance（）之后）记录。

Note that according to the PostGIS documentation, ST_Distance() doesn't use indexes, so you may want to investigate using ST_DWithin() instead (it's documented right after ST_Distance()).

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