[FireDAC] Query.MergeDataset - how to use?

[Jacek Laskowski 57]

How to correctly use the MergeDataset method from TFDQuery?

 

I have FDQuery and FDMemTable, in FDMemTable I have data copied from FDQuery:

 

 FDMem.Data: = FDQuery.Data;

 

...then I modify the record in FDMemTable, and then I extract the differences to a separate FDMemTable:

 

FDMemDelta.Data := FDMem.Delta;  // <--- delta to data

Finally, I want to save these changes (stored in FDMemDelta as data) to the database, so I do:

 

FDQuery.MergeDataset(FDMemDelta, TFDMergeDataMode.dmDataMerge, TFDMergeMetaMode.mmNone);

 

and in FDQuery I see changes ... but I do not know how to force FDQuery to write this changes to the database.

FDQuery.Commit - does not save anything. How commit changes to DB?

 

Edited July 29, 2019 by Jacek Laskowski

[f.m 8]

To write changes to the database, try this:

LQueryDest.CachedUpdates := True;
LQueryDest.MergeDataSet( LQuerySource, TFDMergeDataMode.dmDeltaMerge );

LQueryDest.Connection.StartTransaction();
Assert( 0 = LQueryDest.ApplyUpdates() );
LQueryDest.Connection.Commit();

LQueryDest.CommitUpdates();
LQueryDest.CachedUpdates := False;

A record will be saved if its UpdateStatus is Inserted or Modified.