In QGIS, there is Value Relation widget for fields, that contain references to data in external tables or views. While it works fine for small number of choices, it can quickly become overwhelming, if there are many of them (e.g. when trying to relate multiple businesses with one map item. It seems, that this is a case for autocomplete widget, similar to http://ivaynberg.github.io/select2/ but I am not aware of such a widget and Google didn't help me.
Do you know about such plugin, or should I turn to custom programming?