Unexpected behaviour with FireDAC Master-Detail relationships

Question

I face a problem with FireDAC Master-Detail relationships.

FireDAC has two modes for M/D relationships : Parameter-Based and Range-Based http://docwiki.embarcadero.com/RADStudio/Berlin/en/Master-Detail_Relationship_(FireDAC)

The first one uses parameters on every query to retrieve the correspondent details needed after every scroll, and the second one loads first all the data in the datasets, and set the fields that define the master-detail relationships (filtering the details after every scroll on the master).

You can combine both methods, giving you the advantages of both (querys returning limited records while reduced traffic with the database, offline mode, ...).

It works nice and fast except when one of the details is empty. This seems to be the reason (quoted from the Documentation) :

Combining Methods

To combine both methods, an application should use both Parameters and Range-based setups and include fiDetails into FetchOptions.Cache. Then FireDAC at first uses range-based M/D. And if a dataset is empty, then FireDAC uses parameter-based M/D. The new queried records are appended to the internal records storage.

Also, you can use the TFDDataSet.OnMasterSetValues event handler to override M/D behavior.

Suppose you have

Master BILLS

+---------+------------+
| Bill_Id |    Date    |
+---------+------------+
|       1 | 01/01/2017 |
+---------+------------+

Detail LINES

+---------+---------+------------+
| Bill_Id | Line_Id |  Concept   |
+---------+---------+------------+
|       1 |       1 | Television |
|       1 |       2 | Computer   |
+---------+---------+------------+

Subdetail TAXES

+---------+---------+-----+--------+
| Bill_Id | Line_Id | Tax | Import |
+---------+---------+-----+--------+
|       1 |       1 | 14% | 74.25  |
|       1 |       1 | 7%  | 36.12  |
+---------+---------+-----+--------+

I have those 3 FDQuerys with parameters :

qryBills.SQL = 'select * from BILLS where Bill_Id = :Id';

qryLines.SQL = 'select * from LINES where Bill_Id = :Id';

qryTaxes.SQL = 'select * from TAXES where Bill_Id = :Id';

And the Master-Detail relationship is defined by range

qryLines.MasterFields = 'Bill_Id';

qryTaxes.MasterFields = 'Bill_Id;Line_Id';

If all the details contain records then everything is fine, but when a detail is empty (like in my example, where there are no Taxes for the Line #2) then when I scroll to that empty detail its query is re-launched (as the documentation says) duplicating the records for the not-empty details.

I mean :

1. I open the three Datasets for the Bill_Id #1
2. Everything looks fine, I see the master record, the Line #1 and its two taxes
3. I move to the second line and it still looks fine, the taxes appear empty.
4. When I go back to the first line, now I see two times its two taxes.
5. If I go to the second line again, and return to the first one, now I will see three times its two taxes.
6. ...

The problem is that every time I move to the second line, its subdetail is empty, so it relaunches the qryTaxes query, duplicating its entire content.

Is not uncommon to have empty details, do you know of a way to prevent its query to be re-launched when it happens ?. I can't find it.

Thank you.