Hot answers tagged arcgis
ModelBuilder is old, clunky, and is not getting any significant updates with ArcGIS Pro, if this tweet is any indication. I have never been a big fan of it (though begrudgingly still use it when I have to), so you might consider this answer as a sidestepping of the question and a recommendation to look at alternatives. FME is arguably the most obvious ...
Just as a reminder: also make sure the classes or tables are part of the same geodatabase AND make sure the keyfields on which the join will be operated are of the same type.
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