To pull a value of a link on selection, use the `add_fetch` method.

    
    
    add_fetch(link_fieldname, source_fieldname, target_fieldname)
    

### Example

You create Custom Field **VAT ID** (`vat_id`) in **Customer** and **Sales
Invoice** and want to make sure this value gets updated every time you select
a Customer in a Sales Invoice.

Then in the Sales Invoice Custom Script, add this line:

    
    
    cur_frm.add_fetch('customer','vat_id','vat_id')
    

* * *

See: [How to create a custom script]({{url_prefix}}/user/guides/customize-erpnext/custom-scripts.html)

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