Understanding Agg tables

[Anonymous]

I am trying to get my head around using agg tables to improve DirectQuery response times.

Following guides by Microsoft, Radacad and others I have created a very basic model with a Fact table (Assignments) related to a Projects Dimension (by ProjectID - many to one) and a Date Dimension (by TimeByDay - many to one).  I used PowerQuery to create an Aggregated copy of the Assignments table grouped by TimeByDay and ProjectID and summing Assignment Work.  This Agg table has the same relationships to the Dimension tables.

I have set up the Aggregation mappings and set the Dimension tables to Dual mode and the Agg to Import (original Assignments table remains DirectQuery)

Checking with just a couple fields in a table all seems fine and queries are clearly hitting the agg table with instant results instead of waiting a minute or more.  An Agg table column with any column from the Date table works as expected.  However, the table shows a single row with a blank value for any column from the Projects table.

I'm expecting that I have missed something obvious but I cannot understand why there is a different behaviour for the same kind of relationship between the Fact and Dimension tables.

[Greg_Deckler]

So that generally means that there are non-matching records in relationships. Not sure how else to help.

[Anonymous]

All the ProjectIDs have a match across the tables, the visuals work (slowly) without the agg table setup.
(for my sanity triple checked via copying the columns to Excel to confirm all 1M match in the original table and all 100k in the agg)

[Anonymous · Accepted solution]

Your comment actually did help, problem seems to just be down to curly braces { 🤔😵 }.  I have never really noticed nor cared before that they are added around the Id text values for some reason by DirectQuery:  Direct Query adding curly brackets to Test GUID Fi... 

Since the Agg table is in Import mode it's ProjectId values lack the curly braces.  So any query hitting the Agg table gets no matches for that relationship (queries on the Fact table that don't hit the agg table use the Fact table Ids which still have braces and so work fine)

Solution is adding braces to the Agg table ProjectId (or setting up the Agg in DQ mode but who would want that?)

Would appreciate any further info as this soaked up a lot of time even though the fix is a simple one. Is this just a bug or is there a good reason for the additional characters?