ReferenceProperty存储的是一个key，尝试获取它的值时，会自动访问datastore来get。因此你的做法会访问多次datastore。
get_value_for_datastore就是用来直接获取内部存储的值，也就是key的，因此你可以用它获取所有的key，再用db.get一次拿到。 前面写错了一点，完整的代码应该是这样： db.get(set( [SecondModel.reference.get_value_for_datastore(s) for s in secList] )) 还有不明白的可以看这里： http://www.keakon.cn/bbs/thread-1959-1-1.html ---------- keakon 2010/10/25 saintthor <[email protected]>: > 谢谢。get_value_for_datastore这个函数我没看懂是什么意思。但我要取的是被secList中元素引用的FirstModel的 > 集合，或许应该是 > > set( [FirstModel.get_value_for_datastore(s.reference) for s in > secList] ) > > On 10月23日, 上午12时13分, 风笑雪 <[email protected]> wrote: >> The entities didn't define a cmp opreation, they'll compared by their >> memory address. >> >> You can try: >> set( [s.reference.key() for s in secList] ) >> >> or more efficient way: >> set( [SecondModel.get_value_for_datastore(s) for s in secList] ) >> >> ---------- >> keakon >> >> On Fri, Oct 22, 2010 at 4:00 PM,saintthor<[email protected]> wrote: >> > class FirstModel(db.Model): >> > prop = db.IntegerProperty() >> >> > class SecondModel(db.Model): >> > reference = db.ReferenceProperty(FirstModel) >> >> > first1 = FirstModel(...).put() >> > first2 = FirstModel(...).put() >> > first3 = FirstModel(...).put() >> >> > fList = [first1,first2,first3] >> >> > sList = [] >> > for i in range( 10 ): >> > sList.append( SecondModel( reference = fList[i%3] ).put() ) >> >> > # now, i have 10 SecondModel references 3 FirstModel. >> >> > q = SecondModel.all() >> >> > secList = q.fetch( q.count() ) >> >> > FirstSet = set( [s.reference for s in secList] ) >> >> > print len( FirstSet ) >> >> > # now, len( FirstSet ) should be 3, but there is 10. >> >> > it regards same FirstModel referenced by different SecondModel as >> > different. how to make it regards it same? >> >> > -- >> > You received this message because you are subscribed to the Google Groups >> > "Google App Engine" group. >> > To post to this group, send email to [email protected]. >> > To unsubscribe from this group, send email to >> > [email protected]. >> > For more options, visit this group >> > athttp://groups.google.com/group/google-appengine?hl=en. > > -- > You received this message because you are subscribed to the Google Groups > "Google App Engine" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > For more options, visit this group at > http://groups.google.com/group/google-appengine?hl=en. > > -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/google-appengine?hl=en.
