SQLAlchemy - Is there a way to see what is current

问题:

I'm curious if there's a way to show what is currently in the session?

Or perhaps a way to check if the session is empty or not so that I can do something like the below.

if db.session:
    db.session.commit()

This way it will only commit if there's actually something in the session waiting to be committed.

回答1:

There are following properties to check session state:

• Session.new - for objects, which will be added to database.
• Session.dirty - for objects, which will be updated.
• Session.deleted - for objects, which will be deleted from database.

These three properties can be used to check session state:

if not db.session.new and not db.session.dirty and not db.session.deleted:
    # do smth

However it is safe to call session.commit() even if there is no changes in session. If you don't do something special, you don't need to explicitly check session state before commit.

---

Also there is a private method called Session._is_clean(), which is used to check if there are any changes to be flushed to database. It's implemented like this:

def _is_clean(self):
    return not self.identity_map.check_modified() and \
        not self._deleted and \
        not self._new