Thank you Mike!
I'm going to try this different approach.

El miércoles, 25 de marzo de 2020, 13:30:47 (UTC+1), Mike Bayer escribió:
>
>
>
> On Wed, Mar 25, 2020, at 6:27 AM, Javier Collado Jiménez wrote:
>
> Hello, 
> I'm having a problem trying to cleanup sqlalchemy objects. My application 
> has a thread which handles DB connections. In some cases the thread dies 
> and I want to do a cleanup so, next time the thread is started it would be 
> able to reconnect again.
> The steps I tried are:
>             self.metadata.clear()
>             self.engine.dispose()
>             self.session.close()
>             self.conn.close()
> But when I start a new thread, errors like this appear:
> sqlalchemy.exc.ArgumentError: Column object 'column' already assigned to 
> Table 'table'
>
>
> you should not be calling metadata.clear() and it looks like you are doing 
> something where you are building Table objects on the fly, re-using the 
> same Column objects a second time, leading to the error you are seeing.  
> There should be a single MetaData object that is not part of an object, 
> e.g. it's a global variable in your program (e.g. not "self.metadata").
>
> Similarly for the engine, there should not be a "self.engine", there 
> should be a single Engine object that is also a global variable in your 
> program.  It is also threadsafe and can be shared among multiple threads.
>
>
>
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