@SaheliG 

"An external class (defined through the Connector and Metadata wizard ) may not contain one property that can serve as a handle. To support the Obj-Open-by-Handle method with external classes, a substitute string is assembled from the key columns of the table. "

https://docs-previous.pega.com/system-administration/85/obj-open-handle-method

So yes, but since there won't be a pzInsKey generated by Pega that you can use, you have to construct the pzInsKey yourself by concatenating the class along with the keys defined on the class instance. Then when calling Obj-Open-By-Handle Pega constructs the correct SQL query.

But I'd recommend just using Obj-Open with the keys explicitly defined.

@SaheliG 

External classes do not contain the @baseclass.pzInsKey and @baseclass.pxObjClass properties, which are present in every internal class. In some cases, no single property in the external class can serve as a unique handle. To support the Obj-Open-by-Handle method with external classes, Pega Platform assembles a substitute string from the key columns of the table.

we need to identity the key columns of the table and construct the pzInsKey as below

pzInsKey for external class = external class<space>keycolumn1!keycolumn2