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POSQLAlchemy: Re-saving model's unique field after trying to save non-unique value
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copied!<p>In my SQLAlchemy app I have the following model:</p> <pre><code>from sqlalchemy import Column, String from sqlalchemy.ext.declarative import declarative_base from sqlalchemy.orm import scoped_session, sessionmaker from zope.sqlalchemy import ZopeTransactionExtension DBSession = scoped_session(sessionmaker(extension=ZopeTransactionExtension())) class MyModel(declarative_base()): # ... label = Column(String(20), unique=True) def save(self, force=False): DBSession.add(self) if force: DBSession.flush() </code></pre> <p>Later in code for every new <code>MyModel</code> objects I want to generate <code>label</code> randomly, and just regenerate it if the generated value is already exist in DB.<br> I'm trying to do the following:</p> <pre><code># my_model is an object of MyModel while True: my_model.label = generate_label() try: my_model.save(force=True) except IntegrityError: # label is not unique - will do one more iteration # (*) pass else: # my_model saved successfully - exit the loop break </code></pre> <p>but get this error in case when first generated <code>label</code> is not unique and <code>save()</code> called on the second (or later) iteration:</p> <pre><code> InvalidRequestError: 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) column url_label is not unique... </code></pre> <p>When I add <code>DBSession.rollback()</code> in the position (*) I get this:</p> <pre><code> ResourceClosedError: The transaction is closed </code></pre> <p>What should I do to handle this situation correctly?<br> Thanks</p>

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