11. října 2016

Different approach to Dynamic Row Level Security

There were already written few blog posts both about Row Level Security. I would like to add one more about this topic. I use this pattern for several years in SQL Server Analysis Services. Biggest advantage of this approach is, that you don’t have to fight with table relationships, which can be sometimes tricky to make work correctly.
To follow with steps, you can download sample file, which uses Adventure Works Sample Data.
File can be downloaded here:
Let’s have a look at the report and scenario. Adventure Works sales products, that are grouped to categories. Common requirement is to limit data in report, so category manager would see just his/her category. So if I want to grant access just to “Bikes” I could write DAX row filter
DAX formula:
[Category] = “Bikes”
This could work for few categories. But if you have 40. Role membership would be hard to maintain. Same thing can be handled by one role using configuration table.
For purpose of blog post, I will enter data manually using “Enter Data” option. You can replace data in table with real user names and email addresses. In real life I use for this configuration SQL Server Master Data Services, but any table would do.
Table security can stay unrelated

What I’ll need is to create calculated column to DimProduct table. Let’s call it Security_Category using function lookupvalue searching in security configuration table.
DAX formula
Security_Category = LOOKUPVALUE(security_mapping[CATEGORY],security_mapping[CATEGORY],[Category],security_mapping[USER],"domain\username")
first column is the value I want to return, second is searched column, third value I want to find, fourth second column to be searched, fifth value.
Arguments 4,5 are here to restrict access to particular user if we had multiple users in same configuration table.
DAX filter needs to be evaluated as true value. I can check if anything was found by function ISBLANK function
DAX formula
Security_Category = ISBLANK(LOOKUPVALUE(security_mapping[CATEGORY],security_mapping[CATEGORY],[Category],security_mapping[USER],"domain\username"))
Formula returns now true, where records weren’t found. I need it oppositely and can switch logical value using function NOT
DAX formula
Security_Category = NOT(ISBLANK(LOOKUPVALUE(security_mapping[CATEGORY],security_mapping[CATEGORY],[Category],security_mapping[USER],"domain\username")))
As next step I can create new role Dynamic Security in Power BI desktop and apply Row Filter on DimProduct table referencing calculated column with formula from previous step.
I can check what if visible to role members using View as role Dynamic Security.
To make it really dynamic, I will replace static value “domain\username” with function USERNAME() in formula.
DAX formula:
Security_Category = NOT(ISBLANK(LOOKUPVALUE(security_mapping[CATEGORY],security_mapping[CATEGORY],[Category],security_mapping[USER],USERNAME())))
Function USERNAME behaves differently in desktop where it returns username in format “domain\username” and when published to powerbi.com where it returns email address username@domain.com
Therefore before publihing replace column USER with column EMAIL in DAX formula
Security_Category = NOT(ISBLANK(LOOKUPVALUE(security_mapping[CATEGORY],security_mapping[CATEGORY],[Category],security_mapping[EMAIL],USERNAME())))
In this blog post I covered how to implement dynamic security in Power BI without relationships in data model using DAX formulas. Let me know if you have any questions or comments


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