Question

我有两种：

class Professor(ndb.Model):
    name = ndb.StringProperty()
    email = ndb.StringProperty()

class Student(ndb.Model):
    professor = ndb.KeyProperty(kind=Professor)
    name = ndb.StringProperty()
    age = ndb.IntegerProperty()

我想找到教授名字是“Snape”的所有学生实体。我怎么能这样做？

或者如果我采用https://cloud.google.com/appengine/articles/modeling的“一对多”示例。然后我想找到Contact.name为“scott”的所有PhoneNumber实体。怎么做。

appengine示例仅说明如何过滤PhoneNumber属性。如果我想过滤相关的Kind，即Contact属性，该怎么办？

Answer 1

为此，我建议使用ndb.KeyProperty作为学生模型的属性来引用给定的教授。

class Professor(ndb.Model):
  name = ndb.StringProperty()

class Student(ndb.Model):
  name = ndb.StringProperty()
  prof = ndb.KeyProperty()

使用上述实体种类，可以使用仅限密钥的查询查询名称为“Snape”的所有教授，然后查询所有教授为one of the retrieved keys的学生。

prof_keys = Professor.query().fetch(100, keys_only=True)

if len(prof_keys) < 1:
  print "Cannot a given professor's students"
  return

students = Student.query(Student.prof.IN(prof_keys)).fetch(100)

if len(students) < 1:
  print "Found no students whose professor is Snape"
  return

for student in students:
  print "Found student named {} whose professor is Snape".format(student.name)

Answer 2

你可以这样做。

# professor model
class Professor(ndb.Model):
    name = ndb.StringProperty()
    email = ndb.StringProperty()

# student model
class Student(ndb.Model):
    name = ndb.StringProperty()
    age = ndb.IntegerProperty()

snape = ndb.Key(Professor, 'snape')
Professor(name="Professor Snape", email="snape@blah.edu", key=snape).put()


st1 = Student(name="Akshar", age=18, parent=snape)
st2 = Student(name="Greg", age=19, parent=snape)
st3 = Student(name="Alex", age=18, parent=snape)

st1.put()
st2.put()
st3.put()

# so lets say give me all students that has class with Professor Snape
for student in Student.query(ancestor=snape).fetch(10):
    print student.name

# You should get something:
Akshar
Greg
Alex

如何在Google Datastore ndb（Python库）中实现加入方案

2 个答案: