Converting a transaction key into a measure is straightforward.

If you have an existing transaction key that is a regular field – say [Product_id] in the table ’Product_Price_Table’ – and you need to convert this into a measure, you create a New Measure in your measure table.
Following the example, the DAX for your new measure should be as follows:
Product_id = MAX(Product_Price_Table[Product_id])
For performance optimization when having large dimensions.
Product_id = IF([VALUE],Product_Price_Table[Product_id])
or
Product_id = IF([VALUE],MAX(Product_Price_Table[Product_id]))
Note: The name of the new measure should be identical to the old transaction key. This ensures that the writeback-functionality captures and stores the relevant input data.
When having created the new measure, the old transaction key should be removed from the accoPLANNING visual in the ”Transaction keys” section and replaced with the new measure - see visual to the left.

Complete these steps for every existing transaction key.

Using the MAX() operator is arbitrary and could be replaced with for example SELECTEDVALUE(), as we are merely converting the field into a measure. In terms of performance, it is advised to opt for using MAX() to create the new measure, but in terms of output using either one will deliver the same result.

Introduction