> the error is specifically about a many to many table where it expects
> to delete two rows but only one matches the criteria. If you are
> using more than one session, or removing rows from a many to many
> table using SQL statements, this error can occur.
Sorry, I'am a little confuse abut it. (I have only one session)
I've the next table schema:
convenio(conv_id) <--- conv_pre(conv_pre_id, conv_id, pre_id) --->
prestacion(pre_id) (convenio many to many with prestacion across
conv_pre)
conv_pre has a unique index on (conv_id, pre_id) but conv_pre_id is
the primary key
Then, for simplify, I've this mapper:
mapper(Convenio, convenio, properties={
'prestaciones': relation(Prestacion,
secondary=convenio_prestacion, lazy=True)
}
)
Now, I want to do:
pre = session.query(Prestacion).get(123)
conv = session.query(Convenio).get(1)
conv.prestaciones.delete(pre)
And this, must delete one record from conv_pre table where conv_id = 1
and pre_id = 123 (pre.pre_id)
I don't understand why this error ocurr.
You can explain me, please?
Thanks so much for your help.
>
> Another condition, also mentioned in the original thread, that can
> exactly cause this issue is if you set up two many-to-many relations
> against the same table, instead of using a backref, like:
>
> mapper(A, a, properties={
> 'bs':relation(B, secondary=a_to_b)
>
> })
>
> mapper(B, b, properties={
> 'as':relation(A, secondary=a_to_b)
>
> })
>
> The correct way to do the above is:
>
> mapper(A, a, properties={
> 'bs':relation(B, secondary=a_to_b, backref='bs')
>
> })
>
> mapper(B, b)
>
> hope this helps....
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