add isRelation property

If our model has a property with a realtion (let's say a m:n) to another model, we need a
$extbaseQuery->contains(...) call instead of a $extbaseQuery->equals(...) call.
I add a "isRelation" property to the fields listconfig. Now pt_extlist perform a "contains(...)" extbase query.
Is there a better way to check if a property is a relation to another model?