Can i only store GUID in lookup field?

Hi,

I have created a lookup field based on custom view.

I have a table named Property Master entity  in which PropertyId is unique Key.

But in my Lookup in second entity i need to display Unit number from property master which is not unique field.

i wrote a view to display unit number in lookup and on selection of unit number, i couldnt save unit number in Form

It throws errror that "[FormatException: Guid should contain 32 digits with 4 dashes"

So what i did in my lookup i have changed 

  "<row name='result' id='new_unitnumber'>" +

to

  "<row name='result' id='new_propertymastid'>" +

Now record gets saved but once the record saved instead of showing my unit number which is just 3 digits it shows propertymasterid in the entity.

I need unit number to be displayed there and not proertymasterid