Django查询一对多关系 [英] Django query in One to Many relationship
问题描述
我有2个表,Order和OrderDetails,在OrderDetails我有一个字段'product_type'。
从表中,我希望得到所有的product_type字段一个列表。
Order.objects.filter(pk = 1).annotate(type = F('product_type'))
我想要类型
的值返回所有产品类型的列表,而不仅仅是第一个结果喜欢'椅子'。
Ex: type = ['chair','pencil']
型号:
class Order(models.Model):
user = models.ForeignKey(User,related_name =orders)
class OrderDetails(models.Model):
order = models.ForeignKey(Order,related_name =details)
quantity = models.SmallIntegerField(null = False,blank = False)
product_type = models.CharField(null = False,blank = False)
这不是你可以或应该尝试实现的东西e具有查询语句注释。这是因为注释只能用于聚合函数,如 Count
, Sum
等。
如果我正确理解您的问题,可以在遍历查询集时获取此信息:
for订单在Order.objects.all():
types = order.details.values_list('product_type',flat = True)
您可以通过为每个订单预取相关的 OrderDetail
行来提高效率:
pre>
在Order.objects.prefetch_related('details')中的订单:
types = order.details.values_list('product_type',flat = True)
或者,您可以使用以下方法从每个订单中检索一些值:
$ b $ p $ b queryset = Order.objects.values('id','user_id','details__product_type')
它应该执行单个数据库查询。但是,请参阅这里有关如何运作的说明: https:// docs .djangoproject.com / en / 1.9 / ref / models / querysets /#values
您的查询器将输出dicts而不是模型实例。而您不会得到一个不错的 product_type
s的列表,而您会收到如下重复的行:
[
{'id':1,'user_id':1,'product_type':'chair'},
{'id':1,'user_id' :1,'product_type':'table'},
{'id':2,'user_id':3,'product_type':'chair'},
...
]
...所以你必须将这些行在python中分组到你想要的数据结构:
用于集合导入OrdereredDict
grouping = OrderedDict()
订单中的订单.objects.values('id','user_id','details__product_type'):
如果order ['id']未分组:
grouping [order ['id']] = {
'id':order ['id'],
'user_id':order ['user_id'],
'types':set(),
}
[顺序[ 'ID']] [ '类型']。添加(顺序['details__ product_type'])
I have 2 tables, Order and OrderDetails, on OrderDetails I have a field 'product_type'.
From the table Order I want to get all the product_type fields in a list.
Order.objects.filter(pk=1).annotate(type=F('product_type'))
I want the type
value to return a list of all product types, not just the first result like 'chair'.
Ex: type = ['chair', 'pencil']
Models:
class Order(models.Model):
user = models.ForeignKey(User, related_name="orders")
class OrderDetails(models.Model):
order = models.ForeignKey(Order, related_name="details")
quantity = models.SmallIntegerField(null=False, blank=False)
product_type = models.CharField(null=False, blank=False)
解决方案 This is not something you can or should try to achieve with a queryset annotation. This is because annotations are only usable for aggregation functions like Count
, Sum
etc.
If I understood your question correctly, you can get this info when iterating over the queryset:
for order in Order.objects.all():
types = order.details.values_list('product_type', flat=True)
You can make this more efficient by prefetching the related OrderDetail
rows for each order:
for order in Order.objects.prefetch_related('details'):
types = order.details.values_list('product_type', flat=True)
Alternatively, you can retrieve some values from each order using this method:
queryset = Order.objects.values('id', 'user_id', 'details__product_type')
It should do a single db query. However, see the notes here about how this works: https://docs.djangoproject.com/en/1.9/ref/models/querysets/#values
Your queryset will output dicts instead of model instances. And you will not get a nice list of product_type
s... instead you will get repeated rows like:
[
{'id': 1, 'user_id': 1, 'product_type': 'chair'},
{'id': 1, 'user_id': 1, 'product_type': 'table'},
{'id': 2, 'user_id': 3, 'product_type': 'chair'},
...
]
...so you'll then have to group these rows in python into the data structure you want:
for collections import OrderedDict
grouped = OrderedDict()
for order in Order.objects.values('id', 'user_id', 'details__product_type'):
if order['id'] not in grouped:
grouped[order['id']] = {
'id': order['id'],
'user_id': order['user_id'],
'types': set(),
}
grouped[order['id']]['types'].add(order['details__product_type'])
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