The July 2018 release of Power BI includes a lot of neat new features, like wallpaper and of course getting rid of the big formatting frame on Power BI Visuals, but Composite Modeling really stands out. Have you ever created a direct connection to a tabular model and then wanted to add that one Excel spreadsheet for another sales group or needed to add some economic web data? I have. If I was lucky I was able to get it added to the tabular model. Otherwise I had to give up on the idea. Adding more tables to the model which is using direct query is now possible with Composite Model.
Turning on Composite Modeling
Since this feature was just released, it is still in preview. In order to be able to use it, go to the Power BI File tab then Options and Settings->Options->Preview features, as shown in the picture. You will have to restart Power BI after this option is changed. This option not only turns on Composite Modeling, it also enables Many to Many data modeling.
Many to Many Data Modeling
In Power BI if you have tried to create a join relationship between two columns and one of them has duplicate values, you will get an error. If you need to join two tables and they have duplicate key values, more than likely you are familiar with the work around, which is to create another intermediate table which has a column with unique values to create the relationship. If you hide the table you can almost pretend that it really works. When you have Composite Models enabled in the Preview Features, you can create a direct relationship between tables which do not have unique keys! The Many to many relationship will be created for you in Power BI.
Caveats with the Composite Modeling Feature
Like me after playing around with both Many to Many and Composite Modeling you are probably all ready to deploy these features into production. That is a problem. As Composite modeling is a preview feature, it cannot be loaded to the Power BI Service, for now. It will work as a desktop prototype, but you cannot distribute it, yet.
There is another big factor regarding Many to Many which you may have noticed when trying to get this feature to work. It is not possible to incorporate Many to Many with SQL Server Analysis Services Tabular Models, yet. It is my understanding that Microsoft plans to have this available for Analysis Services data sources, but for now, it is not possible to model them.
If you are planning on releasing either of these two features it is now possible to create and to use them in a desktop prototype. I am looking forward to the day, which I hope will be later this year, when these features are available to be distributed to the Power BI Service.
Data aficionado et SQL Raconteur