Can you do a datediff between one tasks's planned completion date and another?

[RyanMcGee]

I am trying to do this but it's not working: The business wants to see how often there is between the due date of the previous task versus the current task, and if that's less than 2 days. So I am trying to do a datediff between the predecessor planned completion date and the current task, but its coming up blank. I am sure I have the formatting messed up but I am still learning TEXTMODE.

displayname=Task Planned Completion Date Vs Predecessor Planned Completion Date
linkedname=direct
querysort=plannedCompletionDate
textmode=true
valueexpression=ROUND(DATEDIFF(({predecessor}.{plannedCompletionDate}),{plannedCompletionDate}),2)
valueformat=HTML

[skyehansen]

Checking the API explorer, there's no reference for predecessor, so predecessor.plannedCompletionDate shouldn't work. But nice guess.

(i.e. go to the API explorer and look up TASK and then look in the Reference tab for everything that can be a reference (a "reference" is what you've done above). e.g. Project is listed as a reference, so {project}.{plannedCompletionDate} would be a sure thing... too bad you don't want that one.)