[英]Getting only the models related to a Django queryset
I don't have much experience with Django (I'm using 1.3) so I have the feeling on the back of my head that this is a dumb question... But anyway: 我没有使用Django的丰富经验(我使用的是1.3),所以我感到这是一个愚蠢的问题……但是无论如何:
I have models like this: 我有这样的模型:
class User(models.Model):
name = models.CharField()
class Product(models.Model):
name = models.CharField()
public = models.BooleanField()
class Order(models.Model):
user = models.ForeignKey(User)
product = models.ManyToManyField(Product, through='OrderProduct')
class OrderProduct(models.Model):
product = models.ForeignKey(Product)
order = models.ForeignKey(Order)
expiration = models.DateField()
And let's say I do some query like this 假设我做这样的查询
Product.objects.filter(order__status='completed', order__user____id=2)
So I'd get all the products that User2
bought (let's say it's just Product1
). 因此,我将获得
User2
购买的所有产品(假设它只是Product1
)。 Cool. 凉。 But now I want the expiration for that product, but if I call
Product1.orderproduct_set.all()
I'm gonna get every entry of OrderProduct
with Product1
, but I just want the one returned from my queryset. 但是现在我想要该产品的到期时间,但是如果我调用
Product1.orderproduct_set.all()
我将获得与Product1
的OrderProduct
每个条目,但我只想从我的查询集中返回一个条目。 I know I can just run a different query on OrderProducts, but that would be another hit on the database just to bring back data the query I ran before can already get. 我知道我可以在OrderProducts上运行不同的查询,但这将是对数据库的另一次打击,只是要带回我之前运行的查询已经可以获取的数据。
.query
on it gives me: .query
它给我:
SELECT "shop_product"."id", "shop_product"."name"
FROM "shop_product"
INNER JOIN "shop_orderproducts" ON ("shop_product"."id" = "shop_orderproducts"."product_id")
INNER JOIN "shop_order" ON ("shop_orderproducts"."order_id" = "shop_order"."id")
WHERE ("shop_order"."user_id" = 2 AND "shop_order"."status" = completed )
ORDER BY "shop_product"."ordering" ASC
If I could SELECT *
instead of specific fields I'd have all the data that I need in one query. 如果我可以
SELECT *
而不是特定字段,那么我将在一个查询中拥有所有需要的数据。 Is there anyway to build that query and get only the data related to it? 无论如何,有没有建立该查询并仅获取与此查询有关的数据?
EDIT I feel I need to clarify some points, I'm sorry I haven't been clearer: 编辑我觉得我需要澄清一些要点,对不起,我还没有更清楚:
I'm not querying against OrderProduct
because some products are public and don't have to be bought but I still have to list them, and they'd not be returned by a query against OrderProduct
我不是针对
OrderProduct
查询,因为某些产品是公开的,不必购买,但是我仍然必须列出它们,并且针对OrderProduct
的查询不会返回它们
The result I'm expecting is a list of products, along with their Order data (in case they have it). 我期望的结果是产品列表以及它们的订单数据(如果有的话)。 In JSON, it'd look somewhat like this
在JSON中,它看起来像这样
[{id: 1, order: 1, expiration: 2013-03-03, public: false}, {id: 1, order: , expiration: , public: true [{id:1,订单:1,有效期:2013-03-03,public:false},{id:1,order :、有效期:,public:true
Thanks 谢谢
I'm gonna get every entry of OrderProduct with Product1, but I just want the one returned from my queryset.
我将使用Product1获取OrderProduct的每个条目,但我只想从我的查询集中返回一个条目。
You just want which "one"? 您只想要哪个“一个”? Your query is filtering on the
Product
model, so all Users
, Orders
, and OrderProducts
associated with each of the Products
in the returned queryset will be accessible. 您的查询正在根据
Product
模型进行过滤,因此与返回的查询集中的每个Products
相关联的所有Users
, Orders
和OrderProducts
都是可访问的。
If you want one specific OrderProduct
, then you should be filtering as op = OrderProduct.objects.filter(xxxxx)
and then accessing the models up the chain like so: 如果您想要一个特定的
OrderProduct
,那么您应该按照op = OrderProduct.objects.filter(xxxxx)
进行过滤,然后按如下方式访问模型链:
op.product
, op.order
, etc. op.product
, op.order
等
I would have suggested the method prefetch_related , but this isn't available in Django 1.3. 我会建议方法prefetch_related ,但是在Django 1.3中不可用。
Dan Hoerst is right about selecting from OrderProduct
, but that still hits the database more than necessary. Dan Hoerst可以从
OrderProduct
选择是正确的,但这仍然对数据库造成了不必要的影响。 We can stop that by using the select_related method. 我们可以使用select_related方法来停止它。
>>> from django.db import connection
>>> len(connection.queries)
0
>>> first_result = OrderProduct.objects.select_related("order__user", "product")
... .filter( order__status="completed",
... order__user__pk=2 )[0]
>>> len(connection.queries)
1
>>> name = first_result.order.user.name
>>> len(connection.queries)
1
>>> product_name = first_result.product.name
>>> len(connection.queries)
1
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