System.DmlException: Insert failed. First exception on row 0; first error: DUPLICATE_VALUE, duplicate value found: <unknown> duplicates value on record with id: <unknown>.
The above error is triggered in the database layer and caused by a trigger or workflow outside of your main code of block that is bubbling this exception. This is rather difficult to track down especially if you are unfamiliar with the code, I am sharing my procedure in the hopes this saves you time - if you find this helpful drop me a line or follow me on twitter @danielsokolows.
This error is caused by unique field constraint on the object, so the first step is to examine the object and locate the API names of all unique fieds. You can do this through SF direclty 'Setup < Customize < <object being inserted> < Fields' or by downloading the
`src/objects` metadata information and searching for
<unique>; I preffer the latter and actually download ALL matadata information for projects I take over.
Next step is to take the field api names and go over triggers and workflows to find where it is referenced and how, this can be time consuming if there are a lot of entries so I preffer to just search within
In the final step you need to examine the code and figure out which unique field is being populated and how and in effect understand how the duplicate value found error is being triggered. In my situation it turned out to be rather straighforward: