Until a few moments ago i would say yes because it seems logical and fpc raises an exception when trying to set the value programatically.

But while investigating why TAutoIncField.ReadOnly always returns false, i found that, regardless of FReadOnly being set to true in the constructor, this value is overriden in TFieldDef.CreateField throung Attributes.faReadOnly flag.

So i tested in Delphi (TClientDatset and TDbf) and found that TAutoIncField.ReadOnly is false (like fpc).

So what should fpc do:
- Follow delphi behavior and let TAutoIncField.ReadOnly return False?
- Fix TAutoIncField.ReadOnly to return True?

Luiz

As far as I know, you can force a value for an autoinc field, so it is not always read-only. AutoInc means the engine will assign a value if none is .

That's not fixing it, that's breaking it. Readonly have to be false for autoincremental fields.

One widely used method, for example, for using autoinc field and cached updates is setting the values of the autoinc fields to negative values when new records are created. That way you can make master-detail relations without having to apply all updates to the datasets. That's not possible anymore when you make those fields readonly.

Joost.

exception (autoinc fields are read only) both in Delphi and fpc.

Luiz

I'm just confused by the exception that is raised ("autoinc fields are read only") when trying to set a value and by the code in the TAutoIncField constructor that initializes FReadOnly to true.

Attached is a patch that removes this initialization.

Luiz

That's indeed strange. And it would mean that those fields are effectively readonly. I think they shoudn't be. (But to be sure, if it would have been my design, there woudn't be such a thing as an autoinc field.)

I see two choices: make it possible to edit autoinc fields, or make ReadOnly true.

Maybe we should choose the second option, for Delphi-compatibility?

Joost.

The funny thing is that, currently, fpc has the same behavior as Delphi, i.e., the field is effectively read only (fpc and Delphi raise the same exception when trying to set the value) but the ReadOnly property is false. Also, in both CanModify is true.

IMO this is a Delphi bug (Can someone test on > Delphi 7?). A quote from Delphi help:

property ReadOnly: Boolean;
Description
Set ReadOnly to true to prevent a field from being modified. In a data grid, tabbing from field to field skips over ReadOnly fields. To learn whether a field can be modified, use the CanModify property instead. CanModify reflects not only the value of the ReadOnly property, but also any restrictions imposed by the underlying dataset.

[AutoIncField]
Note: Auto-incrementing fields are a function of the database back-end. An application should not attempt to set a field value for an autoincrement field (with or without a TAutoIncField object).

Luiz