Find rows in lookup table that don't match any row in the data table

[unire]

What's the best way (preferably with DAX query functions, such as SUMMARIZE, GENERATE, etc) to find all the rows in a lookup table that have no matching row in the data table?

For example, with a data table like this:

[TABLE="class: grid, width: 500"]
<tbody>[TR]
[TD]Person ID
[/TD]
[TD]Country Key
[/TD]
[TD]Age
[/TD]
[/TR]
[TR]
[TD]581
[/TD]
[TD]1
[/TD]
[TD]25
[/TD]
[/TR]
[TR]
[TD]492
[/TD]
[TD]1
[/TD]
[TD]48
[/TD]
[/TR]
[TR]
[TD]390
[/TD]
[TD]2
[/TD]
[TD]37
[/TD]
[/TR]
[TR]
[TD]410
[/TD]
[TD]2
[/TD]
[TD]29
[/TD]
[/TR]
[TR]
[TD]173
[/TD]
[TD]2
[/TD]
[TD]61
[/TD]
[/TR]
</tbody>[/TABLE]

And this lookup table:

[TABLE="class: grid, width: 500"]
<tbody>[TR]
[TD]Country Key
[/TD]
[TD]Country Name
[/TD]
[/TR]
[TR]
[TD]1
[/TD]
[TD]United Kingdom
[/TD]
[/TR]
[TR]
[TD]2
[/TD]
[TD]Japan
[/TD]
[/TR]
[TR]
[TD]3
[/TD]
[TD]China
[/TD]
[/TR]
</tbody>[/TABLE]

The query would need to return one row (3 - China).

 

[unire]

I think I figured it out.
To get all the rows in the lookup table that don't match any row in the data table, I'm doing this:

EVALUATE
FILTER(
DimCountries,
COUNTROWS(RELATEDTABLE(FactPeople)) = 0
)

And to do the other way around (data rows that don't match a lookup row):

EVALUATE
FILTER(
FactPeople,
RELATED(DimCountries[Country Key]) = BLANK()
)

But I don't know whether there are more efficient solutions.