Forum Discussion
Formula.Firewall Error which disappears after reloading the data model in PBI Desktop
Avoid merging at all cost. Either do the joins further upstream, or use separate dataflows, or let the data model do the work for you.
Hi lbendlin ,
are there other transformations that I should avoid too? Like Invoking custom functions? It seems as if the error also appears for queries that do not have any merging steps at all. Therefore I use the expand function in the PQ UI that generates and invokes a automatically generated function.
Regards
KS
Avoid anything that makes the Power Query engine think it is dealing with separate data sources. If you browse the interwebs you will find all kinds of trickery to create a smoke curtain so that the engine gets confused, and assumes everything is ok.
Small example: declare functions inside your query, not outside.