How do I get the SalesForce record id in a custom field

Question

I wanted to add a simple read-only URL-field to 'opportunities' in SalesForce that contains a link to an external webpage with the 15-char record id (used in the salesforce urls) attached to it . To do this I wen to /ui/setup/Setup?setupid=Opportunity --> fields and created a new field under 'Opportunity Custom Fields & Relationships'.

I chose a field with data type 'URL' and added a default value. I thought
"http://example.com/?sfid="&id would do the trick, but this returns

Error: Field id may not be used in this type of formula

This is a vague error. Is my syntax of a default value wrong, or am i using the 'id' parameter in a wrong way? And what is the right way to do this?

I'm new to SalesForce, as you probably already have guessed.

Answer 1

As the other answer stated - Id will be known only after insert meaning the "default value" trick won't work for you.

You have some other options though:

1. Workflow rule that would be populating the URL field after save.

2. Formula field of type text that uses HYPERLINK function

   HYPERLINK("http://example.com/?sfid=" & Id , "See " & Name & " in ext. system")
   

3. Custom link (similar to custom buttons, they appear on the bottom of the page layout. Search them in online help)

The difference between 2 and 3 is quite minor. Custom links can appear only on the record's detail view while formula fields & other urls are well... fields - so they can be used in reports, listviews etc.

You'd have to decide which version suits you best.