检查GAE Python中是否存在数据存储中的实体
我正在尝试创建(类似于)发票号码生成器。但是,由于在创业时发票可能为零或更多,您如何知道实体是否存在检查GAE Python中是否存在数据存储中的实体,python,google-app-engine,python-2.7,google-cloud-datastore,Python,Google App Engine,Python 2.7,Google Cloud Datastore,我正在尝试创建(类似于)发票号码生成器。但是,由于在创业时发票可能为零或更多,您如何知道实体是否存在 query = "SELECT loanNumber FROM Loans ORDER BY loanNumber DESC LIMIT 1" loanNumbers = db.GqlQuery(query) result = loanNumbers.get() # for loanNumber in loanNumbers: if loanNumbers is None: print
query = "SELECT loanNumber FROM Loans ORDER BY loanNumber DESC LIMIT 1"
loanNumbers = db.GqlQuery(query)
result = loanNumbers.get()
# for loanNumber in loanNumbers:
if loanNumbers is None:
print "Print the first number"
else:
print "Print the next number"
错误
现在这里有一些很好的元数据助手函数: 下面是一个在继续查询和其他代码之前检查
贷款的示例:
from google.appengine.ext.db import metadata
my_kinds = metadata.get_kinds() # Returns a list of entity kind names.
if u'Loans' in my_kinds:
...
请注意,在实际创建贷款实体之前,myu-kinds
不会包含Loans
如果您需要更多的控制,或者更喜欢使用自己的助手函数,这里有一些例子:
from google.appengine.ext.db import metadata
my_kinds = metadata.get_kinds() # Returns a list of entity kind names.
if u'Loans' in my_kinds:
...