django - 跨表序列化 Django REST Framework

Question

我有两个具有多对多关系的模型，我正在尝试使用 Django REST Framework 返回一些 geojson。我要返回的数据是 pub_date 和坐标(由 GeoDjango 中的 PointField 表示)。每次我尝试返回 geojson 时，我都会收到错误消息 Field name 'city' is not valid for model 'Article'。我是 django/geodjango 的新手，这是我第一次使用 Django REST Framework。我已经阅读了文档，但无法弄清楚我哪里出错了(或者甚至可能从哪里开始)。

这是我的模型和序列化程序。

模型.py:

class Location(models.Model):
    city = models.CharField(max_length=200)
    country = models.CharField(max_length=200)
    continent = models.CharField(max_length=200)
    point = models.PointField(srid=4326)
    objects = models.GeoManager()

    def __unicode__(self):
        return u'%s' % (self.point)

    class Meta:
        db_table = 'location'

class Article(models.Model):
    authors = models.ManyToManyField(Author)
    locations = models.ManyToManyField(Location, related_name='places')
    article_title = models.CharField(max_length=200, unique_for_date="pub_date")
    pub_date = models.DateTimeField('date published')
    article_keywords = ArrayField(ArrayField(models.CharField(max_length=20, blank=True), size=10), size=10,)
    title_id = models.CharField(max_length=200)
    section_id = models.CharField(max_length=200)

    def __unicode__(self):
        return u'%s %s %s' % (self.article_title, self.pub_date, self.article_keywords)     

    class Meta:
        db_table = 'article'

序列化器.py

class ArticleSerializer(serializers.ModelSerializer):
    places = serializers.PrimaryKeyRelatedField(many=True, read_only=True)
    class Meta:
        model = Article
        fields = ('places')

我想要的输出:

{
"type": "FeatureCollection",
"features": [
    {
        "type": "Feature",
        "properties": {
            "time": "2013-01-22 08:42:26+01"
        },
        "geometry": {
            "type": "Point",
            "coordinates": [
                7.582512743,
                51.933292258,
                1
            ]
        }
    },
    {
        "type": "Feature",
        "properties": {
            "time": "2013-01-22 10:00:26+01"
        },
        "geometry": {
            "type": "Point",
            "coordinates": [
                7.602516645,
                51.94962073,
                1
            ]
        }
    }

提前致谢!

更新!我设法通过嵌入在查询集中的原始 SQL 查询找到了某个地方，但这不太正确:

serialize('geojson', Article.objects.raw('
select a.id, a.pub_date, al.location_id, l.point 
from article a 
join article_locations al on a.id = al.article_id 
join location l on al.location_id = l.id'),
geometry_field = 'point',
fields=('pub_date','locations',))

结果是这样的:

{  
"type":"FeatureCollection",
"crs":{  
    "type":"name",
    "properties":{  
        "name":"EPSG:4326"
    }
},
"features":[  
    {  
        "geometry":null,
        "type":"Feature",
        "properties":{  
            "pub_date":"2015-04-06T20:38:59Z",
            "locations":[  
                3
            ]
        }
    }

Answer 1

DRF 序列化程序可以做两件事:

1. 将复杂数据(例如查询集)序列化为原生 Python 数据类型

   serializer = CommentSerializer(comment)
   serializer.data
   # {'email': u'leila@example.com', 'content': u'foo bar', 'created': datetime.datetime(2012, 8, 22, 16, 20, 9, 822774)}
   

2. 反序列化原生 Python 数据类型的数据

   serializer = CommentSerializer(data=data)
   serializer.is_valid()
   # True
   serializer.validated_data
   # {'content': 'foo bar', 'email': 'leila@example.com', 'created': datetime.datetime(2012, 08, 22, 16, 20, 09, 822243)}
   

在你的情况下

All I want is to return all article pub_dates and their corresponding article coordinates lat/long's (from the pointField).

你必须做两件事:

1. 使用对象、对象的列表或查询集创建复杂的数据结构。

   在您的情况下，这非常简单，您只需要一个包含所有文章和 prefetched 的查询集位置，以防止对每个 location 进行不必要的数据库命中。

   Article.objects.all().prefetch_related('locations')[:10]
   

2. 创建一个可以序列化此查询集的序列化程序。

   因为你有嵌套的数据结构(一个article可以有很多locations)你最好把它分成两个独立的序列化器。

   第一个只知道如何序列化locations，第二个只知道如何序列化articles，但它将使用第一个article.locations 序列化。

   class LocationSerializer(serializers.ModelSerializer):
       class Meta:
           model = Location
           fields = ('point',)
   
   
   class ArticleSerializer(serializers.ModelSerializer):
       #this way we override the default serialization 
       #behaviour for this field.
       locations = LocationSerializer(many=True)
   
       class Meta:
           model = Article
           fields = ('pub_date', 'locations')
   

最后，您可以通过 ViewSet 组合 1 和 2

class ArticleViewSet(viewsets.ModelViewSet):
    serializer_class = ArticleSerializer
    #read about pagination in order to split this into pages
    queryset = Article.objects.all().prefetch_related('locations')[:10]