Have you ever noticed or wondered why “New Branch” input transformation as shown in below snapshot is not visible there in ADF dataflow?
As you can see that this is clearly visible in the context menu that comes on clicking the “+” sign but sometimes this is not there as shown in the below snapshot and you keep on wondering where this has gone.
See, we just added a new source and “New Branch” is not there. This is not visible until you consume this source at least once in the flow and this makes sense if you try to recall the purpose of this transformation. New Branch is used to provider some faster access to the dataset which has already been read from source. It introduces a parallel copy of the source data but reads it from the cache, not reading it again from the source. You might need to do this when you want to refer to the same input but for a different purpose but at the same not to read the data again from the source e.g. I just used it in a scenario whereby I had to refer to DimDate dimension for two dates columns in the fact table. Though I could use the same DimDate table against two different lookups but I preferred to make parallel copy of it and then rename their source columns so that they matches up exactly with the two different date column names in the fact table i.e.
New Branch was used to make two copies of DimDate source and then “Select” transformation was used to rename one of their columns. There could be more significant uses cases of it but this is I think good enough to understand the concept and their basic purpose, specially the scenario when you want to use “New Branch” but suddenly see that this is not visible in the context menu. Frankly speaking, I had to struggle this for about an hour, the very first time I noticed this and couldn’t find anything quickly on google too so thought to share my experience here.