[fpc-devel]Questions (and suggestions) about TDataset descendants design

[Luiz Américo]

I'm finishing a TDataset descendant and, to conclude it, need help in
the following issues (I'm using fpc 1.9.4):

- Currently neither the TField* classes nor the TDataset descendants
check the ReadOnly property of the Field, making possible to change
field value through SetFieldData. Should descendants do the check?
If it's a open issue, i suggest that the check must be done in TField
scope since doesn't makes sense call SetFieldData to a ReadOnly Field.

- I noticed that TField can call SetFieldData with Buffer = nil. How
Descendant should handle this?. Only one of the descendants check if
it's nil.

- TField supports NULL values?. How Tfield handles them?

- In the currently implemented TDataset descendants (fpc 1.9.4), in
GetRecord methods, grError is only set when GetMode is gmCurrent. Is it
the expected?. If yes, it's possible to remove the DoCheck parameter,
letting the caller check the result (GetRecord is called only twice with
gmCurrent in dataset.inc), and simplifying the GetRecord implementation.
In fact TDataset is checking the result now.

- In TDataset, Append is implemented but InternalAddRecord is not 
called. Is it deliberated?

- TDataset property RecNo is not mapped to GetRecNo SetRecNo

by the way,

While trying to change Attributes property of a TFieldDef object with
include(AFieldDef.Attributes,faReadOnly)

  i get the following error:
Error: Incompatible types: got "ShortInt" expected "TFieldAttribute"

The compiler is using the sysutils constant instead of TFieldAttributes


Thanks in advance
Luiz