0037900: INSERT into an empty dataset fails to set BOF to false

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ID	Project	Category	View Status	Date Submitted	Last Update

0037900	FPC	Database	public	2020-10-09 14:46	2020-10-12 10:46

Reporter	Tony Whyman	Assigned To
Priority	normal	Severity	minor	Reproducibility	always
Status	new	Resolution	open
Platform	x86_64	OS	Linux
Product Version	3.0.4

Summary	0037900: INSERT into an empty dataset fails to set BOF to false
Description	The TDataset.Append method may be used to insert a record into an empty database or to add a record to a non-empty database. It should similarly be possible to use the TDataset.Insert method to add a record to an empty database. However, this is not possible as there appears to be a bug in the internal TDataset.DoInsertAppend method which, while setting FBof to false when called via TDataset.Append, leaves it set to true when called via TDataset.Insert. As a result TDataset.IsEmpty always returns true and it is impossible to read from the dataset. Field data is thus always null. TDataset.Append can always used as a workaround for a bidirectional database. However, this is not possible for a unidirectional dataset as a call to TDataset.Append always results in an exception reporting that the action is not permitted for a unidirectional dataset.
Steps To Reproduce	This problem is easily demonstrated with any editable TDataset descendent after an empty dataset is opened. First invoke: Append; writeln(outfile,'BOF = ',BOF,', EOF = ',EOF); This should show BOF = false, EOF = true. Then invoke Insert; writeln(outfile,'BOF = ',BOF,', EOF = ',EOF); This returns BOF=true, EOF = true.
Additional Information	The fix is probably as simple as adding FBof := false to the DoInsertAppend method. I.e. If Not DoAppend then begin {$ifdef dsdebug} Writeln ('going to insert mode'); {$endif} DoInsert(false); FBof := false; //Proposed bug fix end else begin ...
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Attached Files

Date Modified	Username	Field	Change
2020-10-09 14:46	Tony Whyman	New Issue
2020-10-12 10:46	LacaK	Note Added: 0126252

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LacaK 2020-10-12 10:46 developer ~0126252	I did test in Delphi 7 with TClientDataSet and after Insert there are both BOF and EOF = True. There is also test TTestCursorDBBasics.TestInsertOnEmptyDataset for this situation. So it seems that it is expected behaviour.