Google App Engine Datastore - 在投影和过滤器中使用 StructuredProperty 进行查询

Question

我有几个 ndb 模型如下所示：

class Product(ndb.Model):
    manufacturer = ndb.StringProperty()
    category = ndb.StringProperty()
    price = ndb.FloatProperty()
class Customer(ndb.Model):
    customerId = ndb.StringProperty()
    name = ndb.StringProperty()    
    products = ndb.StructuredProperty(Product, repeated=True)

我想根据他/她拥有的产品的“制造商”和“类别”进行查询。所以这个查询按预期工作。

query = Customer.query(Customer.products == Product(manufacturer=data_json["product"]["manufacturer"],
                                                    category=data_json["product"]["category"]))

results= query.fetch()

但是，我无法让“投影”与此查询一起使用。以下查询根本没有返回任何内容。

query = Customer.query(Customer.products == Product(manufacturer=data_json["product"]["manufacturer"],
                                                    category=data_json["product"]["category"]))

results= query.fetch(projection=[Customer.products.price])

但是如果我使用没有滤镜的投影，投影部分可以正常工作。以下查询将返回所有实体，但仅返回“价格”属性

results= Customer.query().fetch(projection=[Customer.products.price])

有什么想法吗？谢谢。

顺便说一句，我的查询是根据这篇文章开发的。 https://cloud.google.com/appengine/docs/standard/python/ndb/queries#filtering_structured_properties

Answer 1

在 ndb 库中组合 AND 和 OR 操作的正确方法记录在 NDB Client Library's documentation 中。

通过下面的查询，您正在过滤器中执行 AND 操作，因此您应该使用我在下面建议的操作，而不是这个，使用 ndb.AND()。

# Your query
query = Customer.query(Customer.products == Product(manufacturer=data_json["product"]["manufacturer"], category=data_json["product"]["category"]))

# Query using ndb.AND
query = Customer.query(ndb.AND(Customer.products == Product(manufacturer=data_json["product"]["manufacturer"]), Customer.products == Product(category=data_json["product"]["category"])))

另外，如果你执行filtering in multiple steps，查询也有效：

# Your request
query = Customer.query(Customer.products == Product(manufacturer=data_json["product"]["manufacturer"], category=data_json["product"]["category"]))
results = query.fetch(projection=[Customer.products.price])

# Request performing filter in multiple steps
query = Customer.query(Customer.products == Product(category=data_json["product"]["category"]))
query1 = query.filter(Customer.products == Product(manufacturer=data_json["product"]["manufacturer"]))
results = query1.fetch(projection=[Customer.products.price])

尽管我建议使用 ndb.AND()，但您可以使用任何一种建议的替代方法，因为它可以最大限度地减少代码，也是组合 AND 操作的最佳方式。

---

更新带有一些代码：

app.yaml

runtime: python27
api_version: 1
threadsafe: true

handlers:
- url: /.*
  script: main.app

main.py

import webapp2
from google.appengine.ext import ndb

# Datastore Models
class Product(ndb.Model):
    manufacturer = ndb.StringProperty()
    category = ndb.StringProperty()
    price = ndb.FloatProperty()

class Customer(ndb.Model):
    customerId = ndb.StringProperty()
    name = ndb.StringProperty()
    products = ndb.StructuredProperty(Product, repeated=True)

# Create entities for testing purposes
class CreateEntities(webapp2.RequestHandler):
    def get(self):
        prod1 = Product(manufacturer="Google", category="GCP", price=105.55)
        prod2 = Product(manufacturer="Google", category="GCP", price=123.45)
        prod3 = Product(manufacturer="Google", category="Drive", price=10.38)
        prod1.put()
        prod2.put()
        prod3.put()

        cust1 = Customer(customerId="Customer1", name="Someone", products=[prod1,prod2,prod3])
        cust2 = Customer(customerId="Customer2", name="Someone else", products=[prod1])
        cust3 = Customer(customerId="Customer3", name="Noone", products=[prod3])
        cust1.put()
        cust2.put()
        cust3.put()

        # Response text
        self.response.headers['Content-Type'] = 'text/plain'
        self.response.write('Done creating entities')

class GetEntities(webapp2.RequestHandler):
    def get(self):
        # This will not work
        #query = Customer.query(Customer.products == Product(category="GCP", manufacturer="Google"))
        #results = query.fetch(projection=[Customer.products.price])

        # Alternative 1 - WORKS
        #query = Customer.query(Customer.products == Product(category="GCP"))
        #query1 = query.filter(Customer.products == Product(manufacturer="Google"))
        #results = query1.fetch(projection=[Customer.products.price])

        # Alternative 2 - WORKS
        query = Customer.query(ndb.AND(Customer.products == Product(manufacturer="Google"), Customer.products == Product(category="GCP")))
        results = query.fetch(projection=[Customer.products.price])

        self.response.out.write('<html><body>')
        for result in results:
            self.response.out.write("%s<br><br>" % result)
        self.response.out.write('</body></html>')

app = webapp2.WSGIApplication([
    ('/createEntities', CreateEntities),
    ('/getEntities', GetEntities),
], debug=True)