Python 检查 .one() 是否为空 sqlAlchemy
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check if .one() is empty sqlAlchemy
提问by john
I am running a query based off of other ids for the query. The problem i have is that sometimes the query won't find a result. Instead of having the entire program crash, how can I check to see if the result will be None?
我正在运行基于查询的其他 id 的查询。我的问题是有时查询找不到结果。我如何检查结果是否为 None，而不是让整个程序崩溃？
This is the query I have:
这是我的查询：
sub_report_id = DBSession.query(TSubReport.ixSubReport).filter(and_(TSubReport.ixSection==sectionID[0], TSubReport.ixReport== reportID[0])).one()
When the code gets executed and no results are found, I get a NoResultFound exception
当代码被执行并且没有找到结果时，我得到一个 NoResultFound 异常
NoResultFound: No row was found for one()
is there a way to just skip the query if there is not going to be a result?
如果没有结果，有没有办法跳过查询？
Found the solution on SO(couldn't find it before) Getting first row from sqlalchemy
在 SO 上找到解决方案（之前找不到） 从 sqlalchemy 获取第一行
采纳答案by Lynch
回答by kylie.a
How would SQLAlchemy know there wasn't going to be a result without doing the query?
如果不进行查询，SQLAlchemy 如何知道不会有结果？
You should catch the exception and handle it then:
您应该捕获异常并处理它然后：
from sqlalchemy.orm.exc import NoResultFound
try:
sub_report_id = DBSession.query(TSubReport.ixSubReport).filter(and_(TSubReport.ixSection==sectionID[0], TSubReport.ixReport== reportID[0])).one()
except NoResultFound:
sub_report_id = [] # or however you need to handle it
回答by ythdelmar
You can also use one_or_none(), this returns Nonewhen there's no result found and is syntactically clearer than first(). No error handling required.
您也可以使用one_or_none()，这会None在找不到结果时返回，并且在语法上比first(). 不需要错误处理。
ref: one_or_none()
