AX / Dynamics 365 For Finance and Operations blog

Reference article : https://vermaax.wordpress.com/2014/07/30/multi-value-select-for-lookup-in-dynamics-ax-2009/

DialogField dlgField = dialog.addField(…);
FormStringControl fsc = dlgField.control();
fsc.replaceOnLookup(false);

Let’s assume we have lookup for a control

If you put ReplaceOnLookup property to Yes (default), the control will not let you select more than one value.

If you put ReplaceOnLookup property to No (default), the control will let you select more than one value.