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鉴于此功能：

features是 SQLAlchemy 对象的列表

template只是一个字典，表示向用户显示内容的模板

def get_feature_dictionary(features, template):

  feature_list = []

  print features

  for feature in features:

    for field in template.fields:
      if field.data_type == 'geometry':
          geometry = getattr(feature, field.name)
          geometry_string = db.session.scalar(pg_functions.geojson(getattr(feature, field.name)))

    this_feature = {
      "type": "Feature",
      "geometry": json.loads(geometry_string),
      "properties": {
        "id": feature.id,
        "created": feature.created,
        "status": feature.status
      }
    }

    feature_list.append(this_feature)

  return feature_list

我想返回一个如下所示的 GeoJSON FeatureCollection：

{
  "type": "FeatureCollection",
  "features": [
    {
      "geometry": {
        "type":"GeometryCollection",
        "geometries":[
          {"type":"Point","coordinates":[2,0]}
        ]
      },
      "properties": {
        "created": "Tue, 03 Aug 2010 17:11:13 GMT", 
        "id": 1, 
        "status": "public"
      }, 
      "type": "Feature"
    }
  ], 
  "properties": {
    "features_per_page": "", 
    "status": {
      "code": 200, 
      "type": "OK"
    }, 
    "total_features": 1021, 
    "total_pages": ""
  }
}

我可以把它打印出来：

{
  "type": "FeatureCollection",
  "features": [
    {
      "geometry": '{\"type\":\"GeometryCollection\",\"geometries\":[{\"type\":\"Point\",\"coordinates\":[2,0]},{\"type\":\"Polygon\",\"coordinates\":[[[0,0],[1,0],[1,1],[0,1],[0,0]]]}]}'
    ], 
  "properties": {
    "features_per_page": "", 
    "status": {
      "code": 200, 
      "type": "OK"
    }, 
    "total_features": 1021, 
    "total_pages": ""
  }
}

但我最终得到的是一个错误，内容如下：

TypeError: expected string or buffer

TypeError
TypeError: expected string or buffer

Traceback (most recent call last)
File "/usr/local/lib/python2.7/site-packages/flask/app.py", line 1836, in __call__
return self.wsgi_app(environ, start_response)
File "/usr/local/lib/python2.7/site-packages/flask/app.py", line 1820, in wsgi_app
response = self.make_response(self.handle_exception(e))
File "/usr/local/lib/python2.7/site-packages/flask/app.py", line 1403, in handle_exception
reraise(exc_type, exc_value, tb)
File "/usr/local/lib/python2.7/site-packages/flask/app.py", line 1817, in wsgi_app
response = self.full_dispatch_request()
File "/usr/local/lib/python2.7/site-packages/flask/app.py", line 1477, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/usr/local/lib/python2.7/site-packages/flask/app.py", line 1381, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "/usr/local/lib/python2.7/site-packages/flask/app.py", line 1475, in full_dispatch_request
rv = self.dispatch_request()
File "/usr/local/lib/python2.7/site-packages/flask/app.py", line 1461, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
File "[--removed--]/modules/api/views.py", line 116, in index
search = get_search_results(feature_type, conditions, FeatureType)
File "[--removed--]/modules/api/search.py", line 499, in get_search_results
data = get_feature_dictionary(search['results'], template)
File "[--removed--]/modules/api/utilities.py", line 241, in get_feature_dictionary
Display the sourcecode for this frameOpen an interactive python shell in this frame"geometry": json.loads(geometry_string),
File "/usr/local/Cellar/python/2.7.5/Frameworks/Python.framework/Versions/2.7/lib/python2.7/json/__init__.py", line 338, in loads
return _default_decoder.decode(s)
File "/usr/local/Cellar/python/2.7.5/Frameworks/Python.framework/Versions/2.7/lib/python2.7/json/decoder.py", line 365, in decode
obj, end = self.raw_decode(s, idx=_w(s, 0).end())
TypeError: expected string or buffer

我尝试使用更改类型，str()但这只会导致：

ValueError: No JSON object could be decoded

我用 GeoAlchemy (pg_functions.geojson) 和 GeoAlchemy2 (ST_AsGeoJSON) 都试过了，结果相同。我知道我很接近，但由于某种原因，我没有正确传递标量或其他东西。

任何人都知道我做错了什么？

4

1 回答 1

2

我发现我提出ValueError: No JSON object could be decoded错误的原因是因为我没有检查值是否存在。

我改变了这个：

geometry_string = db.session.scalar(pg_functions.geojson(getattr(feature, field.name)))

对此：

geometry_string = db.session.scalar(pg_functions.geojson(getattr(feature, field.name))) or '{}'

一切正常，json.loads()被空字符串绊倒并且无法将空字符串解析为JSON，它至少需要一个空的JSON对象{}

于 2013-12-12T18:55:57.937 回答