Passing Any Arbitrary Value From A Power BI Report To A Dynamic M Parameter

Passing Any Arbitrary Value From A Power BI Report To A Dynamic M Parameter

Dynamic M parameters are incredibly useful in Power BI when using DirectQuery mode because they allow you to pass values from your report direct to your data source query, bypassing Power BI’s own SQL (or whatever query language your source uses) generation layer. However it isn’t obvious how to pass any value you want: dynamic M parameters must be bound to slicers or filters, and they must be bound to tables in your dataset, which means that at first glance it seems like you can only pass values that are already present somewhere in your dataset (for example in a dimension table) to a dynamic M parameter. This isn’t true though: there is a way to allow passing of any value your users enter to a dynamic M parameter and in this post I’ll show you how.

First of all, why is this useful? There are two reasons why you might want to allow passing of any value to a dynamic M parameter rather than binding to a slicer or filter in the normal way:

1. Displaying the list of possible values in a slicer or filter can be expensive, especially if the column you’re slicing on contains thousands or millions of values. It can slow down your report and lead to extra queries being run on your DirectQuery source, which can lead to performance problems.
2. Sometimes the values you want to pass in don’t exist in your DirectQuery source. The scenarios where this is useful are very similar to the scenarios where you’d want to use what-if parameters, but the big limitation of what-if parameters is that you have to pre-calculate all the values that a user might ever want to select and store them in a table. What happens if you don’t want to, or can’t, pre-calculate all the input values?

Let’s see an example of how you can pass any value you want to a dynamic M parameter.

The AdventureWorksDW2017 sample SQL Server database has a table called FactInternetSales with a column called SalesOrderNumber, and let’s say you want to build a Power BI report where an end user can enter whatever SalesOrderNumbers they want and filter the table by them. Let’s also assume that we have to use dynamic M parameters to do this efficiently (which isn’t the case with AdventureWorksDW2017 but could well be in the real world). Here’s what the data looks like:

To set things up in the Power Query Editor you need an M parameter to hold the values entered by the end user. In this example the parameter is called SalesOrderNumber:

Note that the Current Value property is set to a value that is not a valid sales order number, so when no input has been received from the users then no rows will be returned by the report.

Next you need a query that filters the FactInternetSales table by this parameter. Here’s the M code:

There are two interesting things to notice here:

• This code handles the cases where a user enters a single value, in which case the SalesOrderNumber M parameter will be of type text, or when the user enters multiple values in which case the SalesOrderNumber M parameter will be of type list. For more details on handling multi-select in dynamic M parameters see this post.
• The actual filtering is done using the List.Contains M function, which does fold on SQL Server-related data sources. If you’re using other sources you should check if query folding happens for List.Contains for your source.

Thirdly, you need a dummy dimension table with a single column for the dynamic M parameter to be bound to in the report. The dimension table shouldn’t contain any data; here’s the M code to use (the query is called DimSalesOrderNumber):

This query returns a table with a single text column called SalesOrderNumber and no rows:

Once you’ve left the Power Query Editor the next thing to do is to bind the SalesOrderNumber M parameter to the SalesOrderNumber column of the DimSalesOrderNumber table:

Note that the Multi-select property has been enabled. Binding the dynamic M parameter to a table with no rows in means there’s no way a regular slicer could be used with it, because there are no values in the table for the slicer to display.

The last problem to solve is the important one: how do you allow end users to enter any value they want? There are two ways I know of. One is to use the filter pane and the “is” filter type under “Advanced filter”:

The filter pane is great because it’s built-in but it only allows the user to enter one or two (if they use the “Or” option) values to filter on. Remember also that not all filter types are available when you’re using dynamic M parameters.

A better approach, if you’re ok with using custom visuals, is to use the Filter By List custom visual which allows the end user to enter – or even copy/paste in – a list of values: