python - 无法捕获 SQLAlchemy IntegrityError

Question

尽我所能，我似乎无法正确捕捉到 sqlalchemy IntegrityError:

from sqlalchemy import exc

try:
    insert_record()
except exc.IntegrityError, exc:
    print exc # this is never called
    handle_elegantly() # this is never called

正如人们所期望的那样:

IntegrityError: (IntegrityError) insert or update on table "my_table" 
                violates foreign key constraint "my_table_some_column_fkey"

我已尝试明确:

from sqlalchemy.exc import IntegrityError

更新:

我发现一些似乎适合这里发生的事情，在 session 刷新到数据库之前不会引发完整性错误，并且在 try/except 之后 block 已被执行:Trying to catch integrity error with SQLAlchemy

但是，在 try block 中添加 session.flush() 会产生 InvalidRequestError:

ERROR:root:This Session's transaction has been rolled back due to a previous 
           exception during flush. To begin a new transaction with this Session, 
           first issue Session.rollback(). 
           Original exception was: (IntegrityError)

Answer 1

我的 Flask 应用程序也有同样的需求，我按如下方式处理它并且它可以工作:

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from sqlalchemy import exc

db = SQLAlchemy(Flask(__name__))

try:
     db.session.add(resource)
     return db.session.commit()
except exc.IntegrityError:
     db.session.rollback()