Update form.py

flask_admin/contrib/sqla/form.py

+import warnings
+
 from wtforms import fields, validators
 from sqlalchemy import Boolean, Column
 
@@ -158,7 +160,8 @@ class AdminModelConverter(ModelConverterBase):
                     columns = filter_foreign_columns(model.__table__, prop.columns)
 
                     if len(columns) > 1:
-                        raise TypeError('Can not convert multiple-column properties (%s.%s)' % (model, prop.key))
+                        warnings.warn('Can not convert multiple-column properties (%s.%s)' % (model, prop.key))
+                        return None
 
                     column = columns[0]
                 else: