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POSQLAlchemy - difference between mapped orm.relation with backref or two orm.relation from both sides
 

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  1. POSQLAlchemy - difference between mapped orm.relation with backref or two orm.relation from both sides
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    <p>In some project I implement user-requested mapping (at runtime) of two tables which are connected by a 1-to-n relation (one table has a ForeignKey field).</p> <p>From what I get from the documentation, the usual way is to add a orm.relation to the mapped properties with a mapped_collection as collection_class on the non-foreignkey table with a backref, so that in the end both table orm objects have each other mapped on an attribute (one has a collection through the collection_class of the orm.relation used on it, the other has an attribute placed on it by the backref).</p> <p>I am in a situation where I sometimes do just want the ForeignKey-side to have a mapped attribute to the other table (that one, that is created by the backref), depending on what the user decides (he might just want to have that side mapped).</p> <p>Now I'm wondering whether I can simply use an orm.relation on the ForeignKey table aswell, so I'd probably end up with an orm.relation on the non-foreignkey table as before with a mapped_collection but <em>no</em> backref, and another orm.relation on the foreignkey table replacing that automagic backref (making two orm.relations on both tables mapping each other from both sides).</p> <p>Will that get me into trouble? Is the result equivalent (to just one orm.relation on the non-foreignkey table with a backref)? Is there another way how I could map just on the ForeignKey-side without having to map the dictionary on the non-ForeignKey table aswell with that backref?</p>
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