I have successfully created reports with additional Table items (i.e. in the report footer) that share the same main report datasource, and avoid having it re-execute. This works well.
However I now have a different scenario. We use just Designer for building reports, and entity datasources which are all calls to SQL Server stored procedures.
I have a Master datasource, call it M, which is the main report datasource. The detail section has a few fields from M, plus a small Table. I use a Table as you recommend that as more efficient than a subreport. I have a second datasource for details fetched for all master rows call it D. The Table is assigned to D, and I can get a filter condition on the table by referring to a Key field in M. This all actually displays properly, each Table displays the proper 2 or 3 rows filtered out of the entire D result set.
However, the datasource D is being re-executed for every master Detail section being displayed. I somewhat expected that, but still is very bad.
Also just as a bonus, I have one additional table in the report Footer and refers to the same datasource D and summarizes that data, and of course it causes the datasource D to execute yet one more time.
I have read many articles here but I have not seen a master-detail example using entity data source, and just Report Designer, and avoiding the multiple re-executions of the D datasource. I have done a similar layout in SSRS and the detail datasource is executed only once then shared, but I can not find the equivalent implementation using your Report Designer. Thanks.