I've been working with my current company for over two years now.  During that time, on my own initiative, I decided to review the BI market to see what tool(s) that the company should be looking at adopting.  There are quite a few restrictions, data privacy, our clients are very cautious about their data.  So must be an on-premise server and yes I have asked lots of questions about this.  Also, our clients are mostly non-profit or charities, the budget is a massive consideration.  

Whilst working on developing some reports for our Service desk l was asked if we could just return a dataset containing the last 6 and 12 months of data.  This is the type of request l would normally use a TSQL script to resolve.  In this case one of the purposes of this project was to allow us to dog food both PowerBI and also self service BI more generally.

The challenge was quite simple find a way to filter data in a dataset based on specific datetime. to this with a specific date-time using the UI is very simple.  In Figure 1 below l will filter the column titled Issue_Created, which contains date-time values.


Figure 1 - The field 'Issue_created' selected showing the filter icon

From the list l can use this to filter by certain dates as shown below in Figure 2.  This lead me to wonder if it was possible to filter by date ranges.

l 
Figure 2 - Filter by specific date

Below is a video showing how to filter records that either equal or occur after specific date, see Figure 3.

Figure 3 - Creating a filter to show record on or after a specific date.

Once l had set up the filter l then opened the 'Advanced Editor' to look at the M Code.   The code that does the filtering looks like this 

#"Filtered Rows1" = Table.SelectRows(#"Filtered Rows", each [Created] >= #datetime(2015, 7, 7, 5, 16, 52))

The syntax looked relatively simple and straightforward, one of the main challenges is that in the snippet above the datetime is static not dynamic.  At this point there was a tweak to the specification, my internal clients l have every faith in me :-).  What they required was based on today's date, get the first day of the month and then return first day of the month 6 months and 12 month before.  This is a pattern which l have done many times in TSQL, this was going to be a bit more of an adventure.

Long story short, after some experimenting l arrived at the following formulas

= Date.AddMonths(Date.StartOfMonth(DateTime.LocalNow()),-6)
First day of the month 6 months ago based on current date

= Date.AddMonths(Date.StartOfMonth(DateTime.LocalNow()),-12)
First day of the month 12 months ago based on current date.

Whats the next step?  Create a variable which will contain the DAX formulas that have created above.  The first step to open PowerBI desktop and go to 'Edit Queries', this will open the 'Query Editor' window.  In the 'Query Editor' window click on the 'New Source' button and select 'Blank Query' from the pull down list see Figure 4.

Figure 4 - Creating a new Blank Query to act as a parameter

Now the blank query has been created the next step is to name the parameter, the name that l use in the example is Previous_FDM_6Months.  Next l type in the DAX formula -> = Date.AddMonths(Date.StartOfMonth(DateTime.LocalNow()),-6).  Once thats done, then click the green tick to update and evaluate the parameter.

Figure 5 - Setting the parameter name and inserting the DAX formula

So now l have parameter which returns a datetime value based on current date and time.  The last step was to amend the part of the M code l had grabbed earlier to filter the dataset.  Below is the line from the M code l use in production

let
    Source = Sql.Database("A_Cloud_Database","Some_Data"),
    dbo_Some_Data = Source{[Schema="dbo",Item="SomeRandomData"]}[Data],
    #"Filtered_Rows_Last12_Months" = Table.SelectRows(dbo_Some_Data, each [Issue_Created] >= Previous_FDM_12Months),
    .........

The data is extracted from the database and filter only return data where the Issue_Created is equal to or greater than the datetime value returned by the parameter Previous_FDM_12Months.

A complete reference of all the datetime functions in power query lanague aka M can be found here https://msdn.microsoft.com/en-us/library/mt296608.aspx.  If you want to download a PowerBI desktop file with the functions you can download it here.

So first l created a variable in the query window see figure 1.

Figure 1 – Select 'Blank Query' from the new source options

When the  blank query window opens, replace the text 'Query' with the name of the variable, then enter the value that will be returned from the variable.    See Figure 2 for details  


Figure 2 – Showing location of the variable name and where value should be placed.

In figure 3 what l have done is to enter the client name that will be used in the example 'Rainbows' and changed the variable name to 'ClientName'.  Once completed those details then click on the 'Close & Apply' button.


Figure 3 – Showing the client name and variable name.

Once returned to the main PowerBI desktop window, find the newly created dataset in this example it is called 'ClientName' with a field called ' ClientName'.  Now that the variable has been surfaced its time to use.  So let create a new measure, expand out the dataset click once with mouse on the ellipsis and select 'New measure' from the list see figure 4.


Figure 4 – Creating a new measure

When the new measure dialog box appears in this example l created a measure called 'TicketsTextBox' as  l want to the measure to appear in a box containing text.  Which is the reason for my naming convention.  The measure l used is as follows

TicketsTextBox = CONCATENATEX(ClientName,[ClientName]) & "- Tickets"  
 
In figure 5 you can see the newly created measure.


Figure 5 – showing the measure 'TicketsTextBox'

The next step is to get this measure on the report canvas, so insert a card visualization on the report canvas.  Then drag the measure to the values section on the visualization configuration section.  Click on the paint brush icon and expand out the 'Data label' section adjust the size of the label to the desired size.  Then turn off the 'Category Label.  These steps are shown in the video below.

Now you have a card with dynamic title, if you want to change the client name all you have to do is change the text in the variable. A sample PowerBI report file can be downloaded here which contains the report shown above.