Hello @alexis ,
Thanks for the question and using MS Q&A platform.
The drop-down menu used to select what to flatten ("Unroll by"), is populated by the schema (in the source) and anything added from previous transformations.
So when the source schema is empty, it has nothing with which to populate the list of stuff you can flatten ("Unroll by").
I suspect the "dynamic" source is clearing out the schema.
I recall the flatten transformation gave me much trouble when I wanted to do something without schema. I think I ended up going with derived column and the
unfold function. The unfold function is a lot like the flatten transformation, but it can be used as an expression.
There may yet be another option in defining an expression, like using
Before I get too far afield, what did you mean by static vs dynamic source? I thought you meant something like, a rest source whose relative URL changed, or a parameterized linked service, or a sql table chosen at run-time. Something which would break the guarantee of a stable schema.
Please do let me if you have any queries.
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