Understanding why RELATED doesn't work

[Anonymous]

Hi all, 

Hoping not just for the answer but an explaination if possible:

I've always had an issue fully understanding RELATED, the function requires Row-context (makes sense), however, I've tried to impliment the following VAR and i'm returning the following error:

ADDCOLUMNS(SUMMARIZE(fact_opportunity_line_ledger,fact_opportunity_line_ledger[Opportunity Id]),
"TEST", related(Opportunity[Opportunity Id]))

The column 'Opportunity[Opportunity Id]' either doesn't exist or doesn't have a relationship to any table available in the current context.
 

My understanding here is that Summarize creates a row context, so in theory, this should work... is it because of the following:

1) Summarize isn't an iterator and therefore requires an iterator? 

2) is Summarize not row context like I've been thought to believe?

Essentially I want to reference a field in a 1:n relationship in order to create a calculation within a measure. However, I need row context at the op level so that the calculation is correct, and not incorrectly aggreating based on the sum of said column. I

Thanks for reading!

[ThxAlot · Accepted solution]

Your guess makes sense; to my understanding, SUMMARIZE() isn't an typical iterator which provides row-by-row row context; it produces both a row context and a filter context after summarizing. 

SUMMARIZE – DAX Guide

You can tell the nuance when making comparison with a typical iterator like SUMX() SUMX - DAX Guide